Tropical Storm Blanca Finally Named

If anyone checked visible satellite loops yesterday over the eastern Pacific you know that Blanca has been spinning away very impressively for at least 24 hours. Guess it escaped official detection because of the Holiday weekend. Looks like it will track too far to west to initiate a surge up the Gulf of California. Latest IR image above (on blog).

So we’ll continue to watch, after two very suppressed days here locally, for some feature to push the subtropical, low-level moisture back north. Looks mostly hot – the 0.77” we got here at house has been quickly sucked back into the atmosphere, and I’ll have to be watering the plants again this afternoon.

Bob

From Art Douglas re Sea Breeze SW Arizona Yesterday

Sea Breeze Induced Thunderstorm Activity in Southwest Arizona

Monsooners.........

The last couple of days there have been well developed sea breeze fronts in Sonora. Looking at these two pics looks like Organ Pipe had sea breeze induced thunderstorms today....what ya think? Too bad there aren't obs down there!

Art

Dry Out and Heat Up

The period of active storms and significant rains ended in the greater Tucson area about 3 am yesterday morning and the rest of the 4^th was quite suppressed – at least wrt thunderstorms although there was a great fireworks display at one of the foothills resorts early last night. The stormy period began here Monday afternoon, so there were five straight days with storms somewhere in the greater metro area. Now the question is: how long before storms return to the local area?

The morning Tucson and Phoenix soundings today indicate that there’s no CAPE available at low elevations and convection will probably be limited to higher elevations in the east and the borderlands. The Phoenix sounding indicates that drier low level air will be spreading southeastward from the deserts.

The models continue to keep very light winds over southern Arizona in middle levels as the west to east extended ridge continues almost overhead. The anticyclone builds back over the Southwest after a couple of days but the models indicate a much drier atmosphere when this happens. As the desert heats ups, surface pressures will continue to fall (they’re down about 2-3 mb over the state in past 24 hours) which will be something to watch. The models also continue to indicate a tropical storm tracking southwest of Baja, so the exact path of this feature will be of interest. Regardless, the first full week of July will apparently be a lot less interesting, meteorologically, than was the spectacular end of June/start of July.

A Report From Up North

A storm report from up north. The ring of fire set up late afternoon nicely on doppler radar. Gila County had repeated activity with heavy rainfall and pea size hail reported. Spotters also called in with wind gusts over 50 mph,downed fences and an isolated dust storm.

Measurable rain totals were observed across much of Maricopa County even though the corridor along I-17 remained dry. The Southern portion of the county had the highest totals with 1.30 inches at Watermans Wash falling from 2115 to 2200. Check out FCDs website for rainfall amounts:

http://www.fcd.maricopa.gov/RainfallPHX.htm

At Sky Harbor Airport, the precip sensor is showing a minimum of 0.03 inches of precip from last night's activity and ponding remains scattered along the tarmack.

Melissa Wagner

Nice Storm Event Last Night

Fireworks! Graphic from Art Douglas showing total lightning strikes from 26 June through yesterday morning at 1300Z on the 3rd of July. Quite amazing week.

Widespread Rain Event Last Evening to Early AM

During the day yesterday there were some storms drifting around, mainly over higher terrain, with fairly limited coverage. However, storms developed in the southeastern Phoenix area late in the afternoon and produced several damaging winds. Flow in the lower troposphere was light but NW to N and organized outflow apparently got going and headed southeast in our direction. It had really cooked up during the afternoon at lower desert elevations – temps around 105F with dewpoints holding in the low 60s.

After two early thunder events with no rain (around noon and again around 7 pm), thunderstorms rolled in about 9 pm with lots of lightning and thunder. No downpours here at house but an extended period of moderate rains that totaled up to 0.77”, the first rain this summer of any substance here at house (house is 32.27N 110.93W at about 2369 ft MSL – Tucson airport is at 2641 ft).

While rainfall affected perhaps 20 to 30% of eastern Pima County during the day, all of the ALERT gauges recorded measurable rainfall after 7 pm, with many substantial amounts! For example, 33 of 93 sites recorded more than an inch of rain and there were four spots that measured more than two inches. Most of the rains fell between 8 pm to 3 am. So, quite a rainfall event!

In this part of town, since it was the first serious rain, there are some spade foot toads out and about and lots of ants and termites swarming about this morning. The Rillito wash is running nicely and the air is fresh and clean – a great start to the fourth of July. Hope everyone has a great holiday.

Bob

PS – Mike Leuthold hopefully was back from Minnesota to see this one.

Prospects for Today (Friday Jul 3 2009)

This morning’s TWC sounding indicates that considerable CAPe is again present. precipitable water remains near 40 mm, although drier air above 400 mb may inch its way across eastern pima County this afternoon – the upper-level dry line lies north to south across the county and has been fairly stationary this morning. The very thick cloud plume from Sonora has shifted eastward and covers only the southeast corner of Arizona but much of New Mexico. A distinct, but weak, shortwave is now positioned to the east of Tucson and winds below 500 mb are mostly from the north with very light speeds. Anvil level winds have become more westerly and this trend will continue according to models. Steering winds are weak and storms will go wherever their outflows and small-scale CAPE distributions take them.

The NAM 500 mb initial analysis – see above - indicates a string of 500 mb vorticity maxima along the east coast of the GoC (looks a bit like 2-delta noise) – but with no soundings from Mexico this morning, it is unclear how accurate this initialization might be, since it is primarily driven by the previous NAM forecasts. Interestingly, the NAM predicts a consolidation of the features over eastern Arizona and the GoC into a single shortwave that moves back to the northwest, making the weekend quite wet and stormy – at least in the model’s world.

As for today – definitely more sunshine to cook things up. Ample CAPE for storms that will drift about some given the lack of any clear steering flow. Heavy local rains possible in spots – a wet microburst or two also possible. Should be an interesting day and possibly weekend also. I’m going to guess that we have a 50-50 chance for rain here at house today since the weak northerly flow could let Catalina buildups drift our way.

Summary of Yesterday (July 2, 2009)

The above is 24 hour radar estimated rainfall from KEMX (the Tucson Doppler radar) sent by Art Douglas. While these radar estimates tend to be high, they indicate very well where the strong storms occurred yesterday afternoon. Eastern Pima County and the Tucson metro area had considerably less thunderstorm activity than during previous couple of days. The strong storms over the Tucson mountains provided lots of rumbling thunder here at the house but only some spits of rain and another day with just a Trace.

The strong storms that drifted north from the Catalina Mountains produced 1.41" of rain at the Oracle Ranger Station. Only 23% of the gauges in the Pima County Alert network reported measurable rain in past 24 hours, down from 70% on Tuesday and 46% on Wednesday. Five higher elevation stations did report over half an inch yesterday.

I see that Sky Harbor airport in Phoenix had 0.01", so they're batting about the same as we are here at house.

The radar estimate also indicates the large area of Sonora that had very strong storms and intense, very cold-topped clusters yesterday.

Brief Summaries

Yesterday was not as active as Tuesday. There were lots of storms but steering level winds weakened during the day in southeast Arizona and anvil level winds became southerly. Thus, here at house the early storms down on the south side of metro area anviled us out and this was reinforced by more thick anvil clouds coming up from the borderlands.

The visible image from 0100Z yesterday evening shows how widespread storms were across the Great Basin and Southwest, into California. The Pima County ALERT network had measurable rain at 46% of the gauges but amounts were much smaller than on Tuesday. Only 3 stations had ½ inch or more – with 1.93” at Arivaca being the only amount over an inch. Here at the house we had a Trace in some light anvil sprinkles at dark. I also see that storms avoided the Phoenix area once again.

Today – once again heavy debris cloud and a few showers cover the central part of the state. There appears to be a bit more CAPE today with the lifted parcel having theta-w of 23 to 24C this afternoon (but the slopes in Sonora appear to have 26C which will produce very deep storms again today with very cold tops) – assuming some good sunshine. Skies are clear along the eastern portions of the state. Local heavy rains are main threat today. The shear profile remains quite bad with anvils streaming out in same direction storms will be trying to move. Don’t get rain here at house in this flow pattern unless something bubbles up almost right overhead. Also see the NAM precip forecast has another donut hole over the Phoenix area this evening.

Roger Edwards Wrote

Bob typed:
>they were propagating along and toward higher elevations where there was more CAPE available.

Jack Hales and I noticed this once the gust front got into Old Mexico too: Storms would fire on the north slopes and peaks of the short little ranges S of the border, but not in the basins. It was as if the lift atop the outflow density current struck a convective match on every mountainside.

===== Roger =====

I have lived here enough summers now to have watched in frustration many afternoons as storms that were heading right toward the house veered off along the flanks of the Catalinas or turned left (as on Tuesday) and ran down the flanks of the Rincons. A difference of just 1000 ft in elevation out here can affect CAPE enough to influence how and where storms propagate.

Bob

Art Douglas Wrote

Very wet end of June in Ash Canyon on the far southeast side of the Huachucas:

June

9: .07

14: .31

22: .12

25: .16

26: .37

27: .27

28: T

29: 1.50

30: .24

Total 3.04" (30 year normal is 0.82")

Note - if someone wants to check to see just where this is, enter "Ash Canyon Arizona 85615" into Google maps. Obviously the summer rains came right in with summer down near Art's property!

Another Active Storm day in Southeast Arizona

Heavy storms moved across the Tucson area for the second straight day yesterday. The radar loops show several pronounced outflows played roles in the detailed evolution of the storms. photo above shows a large thunderstorm moving across the east flanks of the Catalinas. This storm produced a strong outflow, again with lots of blowing dust. Winds at house were around 40 mph but there was only 0.03” of rain as the storm moved to the south and weakened over downtown. New and more intense cells formed to the west and south.

Data from the Pima County ALERT network indicated that ~70% of the sites had measurable rainfall, with 4 stations reporting over an inch of rain. Brawley at three Points (west of downtown on the other side of the Tucson Mountains) reported 2.20 inches of rain and there was wind damage associated with this storm cell.

Heavy clouds and continuing showers are between here and Phoenix this morning. The TWC sounding was modified by the deep clouds and is not representative of the larger-scale environment – making the forecast situation difficult. A special sounding at 18Z might prove very useful today.

Regardless, precipitable water values are now very large – about 1.75 inches or 45 mm. The NAM predicts that a weak shortwave at 500 mb will be affecting south-central Arizona this evening and that vertical wind shear will again be favorable for strong storms. It appears that storms will occur over a larger portion of the south half of state and that the Phoenix area may be affected today. The details, of course, depend upon the evolution of the current messy cloud/shower situation and how much sunshine and heating occur this afternoon. But definitely another interesting weather day.

Melissa Wagner Wrote:

I just wanted to comment on the storms last night in terms of northern activity. (Grad meteorology student at ASU). Maricopa County had a beautiful, long gust front pass through. While no activity occurred over PHX metro. The NNW portion had impressive storms fire up with great lightning and rain shafts seen from miles away. FCD-Maricopa had recorded 0.43in from 1844 to 1859 at Lake Pleasant. There were other hotspots in the NW, but not as impressive. The NE steering flow and that gust front gave the NNW portion of Maricopa County its first taste of the monsoons.

Summary of Yesterday’s Storms

Thunderstorms were more widespread over southeastern Arizona yesterday afternoon. There was measurable precipitation at almost all reporting stations south and east of a line through Alpine – Saguaro RAWS – TUS – Sells RAWS. Many of these stations also had gusts of 30 mph or greater. There were two severe wind reports logged at the Storm Prediction Center this morning, and it gusted to almost 90 mph at the Atmospheric Sciences building (5th floor roof). Here at the house we had 40 to 50 mph winds that were carrying a heavy load of dust and grit – quite an ugly evening. No rain though, since there was little CAPE by afternoon at the lower elevations. A pronounced gust front raced into the lower desert northwest of Tucson but no new storms were triggered. Even though the steering winds were from the east-northeast, the cores of the heaviest storms propagated almost due south – they were propagating along and toward higher elevations where there was more CAPE available. In the Pima County ALERT network 36 stations had measurable rainfall in past 24 hours and these were mainly the eastern and southern sites.

Yesterday was the first day with widespread, heavy to severe storms occurring in a summer flow pattern! The visible satellite image above shows the impressive array of storms during the late afternoon.

Today’s TWC sounding appears to have similar CAPE to yesterday even though precipitable water is down a few mm. The morning steering level winds are srong from the east but NAM indicates the winds will weaken during the day. I don’t have time for an extended discussion since I’m on my way to several morning appointments.

Important Changes Noted This Morning

The 500 mb anticyclone still has three lobes this morning: one over southern Utah, one over far west Texas, and one over Texas/Louisiana border. The two eastern lobes are quite weak and the western lobe is predicted to dominate and to continue building toward the Four Corners. Middle-level temperatures are quite cool within the main anticyclone (-7 to -10C) and will help increase CAPE over much of the Southwest.

An inverted trough lies across New Mexico from the boot heel to the northeast corner and will probably brush across extreme southern Arizona and the borderlands this afternoon and evening. The vertical shear profile, both in this morning’s TWC sounding and in the NAM forecasts, is quite favorable for storms to propagate from the mountains into lower elevations.

The amount of low-level moisture has continued to slowly increase and the TWC sounding has 1.6 inches of precipitable water this morning. The southeast winds at low-levels may act to increase this some during the day. This morning’s sounding indicates that there will be decent CAPE this afternoon at low elevations with parcels at top of the boundary layer having theta-w values of about 23C or perhaps a bit higher.

All of this seems to come together for an active storm day in south central Arizona, after several days with the storms limited to the far southeast. My guess for this afternoon and evening is that it’s a 50/50 toss up for storms and rain here at the house. Given the shear profile there’s also a good likelihood that some storms may reach severe levels. So, it appears that a more interesting day is on tap.

Other things of note this morning – storms decayed over the GoC as they moved southeast from Sonora (see WV image on blog); large upper cyclone or inverted trough moving across north-central Mexico; another push of low-level moisture noted at Yuma as Td increased 10F from midnight to 1 am and there are widespread clouds across the lower Colorado Basin this morning; the past 24 hours saw no measurable rain over the Pima County ALERT gauge network.

The 500 mb Anticyclone and the TWC Sounding this Morning

1 – This morning the 500 mb anticyclone exhibits three separate centers: one over southern Nevada, one over eastern New Mexico, and one over southern Arkansas. Yesterday morning there was only one distinct center and that was over northeastern Oklahoma. So, the transition that has been advertised by the models is underway. By 72 hours the NAM indicates that the two eastern lobes of the high have been pushed south and weakened/dissipated, while the Great Basin anticyclone dominates and shifts to northern Arizona. This would leave us with a fairly typical summer pattern to begin the month of July.

There is also a distinct inverted trough at 500 mb this morning that stretches from northwest Texas to the southwest Mexican coast. The models seem to indicate that this feature looses its coherence with time and becomes several fragmented vorticity maxima. In some ways it appears that the NAM is behaving as it did last summer - generating numerous small-scale waves and vorticity maxima over northwest Mexico and the Gulf of California. The user is then left having to decide if the model is actually capturing atmospheric reality for any given forecast cycle.

2 – This morning’s TWC sounding, see above, provides a nice illustration of how precipitable water values can be high (as per 1.4 inches plus this morning) but with CAPE values quite low or non-existent. I’ve shown an estimated sounding for 5 pm this afternoon (it may be a bit optimistic since I’ve used 8 g/kg as the mixed boundary layer’s moisture content). There is only a sliver of CAPE present. So, again today, better CAPE values will mainly be restricted to higher elevations. The afternoon’s estimate has a lifted parcel with theta-w of 22C – a marginal value. For really serious thunderstorm potential here in Tucson I’d like to see a lifted parcel with theta-w of 23 to 25C.

It is interesting that there is a shallow layer of easterly winds near 600 mb (i.e., around cloud base). These winds may try to push some mountain developments toward the west, but the dominant steering flow should be the south-southwest winds between 300 and 400 mb.

PS – Storms yesterday in Arizona tended to occur mostly in the southeastern corner of state – southeast of a line from Alpine through Sasabe. The highest amounts I found online were 0.96” at Tombstone and 0.31” at the Carr RAWS station. One station in the Pima County Alert network recorded precipitation (0.04”) in past 24 hours.

Bob

LARGE THUNDERSTORM COMPLEXES OVER NORTHWEST MEXICO LAST EVENING

The most widespread storm activity of the season occurred over northwest Mexico last evening. See IR image from 0300 GMT above. This is an encouraging sign and the activity may have played a role in triggering at least a shallow GoC surge at Yuma early this morning. Note that Td jumped 8F between 6 and 7 am and was still at 69F at 9 am this morning.

Precipitable water continues to increase slowly over south half of state and influx of low level moisture at Yuma will help continue this trend. CAPE at low elevations remains very limited and more boundary layer moisture would help, particularly as 500 mb temps are increasing.

Yesterday there were no reports of measurable rain from the Pima County Alert network of 90+ gauges.

Last weekend the ECMWF and GFS were at odds concerning the large middle level anticyclone that was over the Plains states, with the GFS indicating a westward shift toward the Four Corners. The anticyclone remains over northeastern Oklahoma this morning and the ECMWF clearly was better on that feature. It was however too wet over much of the Southwest.

This morning all three models (NAM, GFS, and ECMWF) are in agreement that the strong, shortwave trough, currently over southern Canada southward to Colorado, will dig southeastward over the Great Lakes and push the anticyclone westward to the Four Corners region by 72 hours. So, a considerable readjustment of the large-scale pattern will be occurring during next couple of days.

There may be some afternoon storms today at lower elevations, given the low-level moisture trends, but CAPE will be highest over the mountains. Chance of rain remains close to zilch here at our house.

Bob

FEW QUICK OBSERVATIONS THIS MORNING

Surprisingly little in way of strong mountain storms yesterday; confined mostly to the far eastern part of state.

About 5% of Pima County gauges had measurable precip last 24 hours – max being a pathetic 0.08” on Mt. Lemmon.

Here at house a Trace with a couple of spits and sprinkles. But a nice cool day because of all the cloud.

This morning the upper-level moist plume is pushing back to the east as the cool Pacific trough has moved onshore.

TWC morning sounding – winds have shifted to west to southwest at all levels; precipitable water up to about 1.4 inches; but low-level moisture and CAPE not really there yet – although, there is a slight bit of CAPE indicated for low elevations.

The cooling at 500 mb indicates that there may be more in the way of mountain storms today, if we get some heating at higher elevations.

Looks like the drier Pacific air may take over for a day or two.

Very moist air mass continues to the south but with no obvious features to push it northward – perhaps convection will increase over Sierra Madre Occidental foothills?

What has happened to the winds aloft on the Mexican soundings? They have gone missing for at least a week now!

Very significant convection with the strong tropical wave in the Caribbean – NAM indicates that this wave will move into Gulf of Mexico – something interesting to watch.

Chance for rain here at house again about zilch for a real storm – steering flow is bad, unless something would develop immediately to the southwest.

Bob

THE IMPORTANCE OF MOISTURE RECYCLING IN SOUTHERN ARIZONA

The plume of subtropical, middle-level moisture covers all but northwest Arizona this morning. However, the Tucson sounding (above) illustrates that very little low-level moisture has accompanied the plume. It appears that high values of low-level moisture have reached north to the Guaymas and Hermosilla areas and the only cold cloud tops are isolated in the southern half of the Gulf of California. Thus, we start the day again with no CAPE at low elevations, thick middle cloud layers, and a hope that the high elevations will heat and convect much more this afternoon than happened yesterday.

The current situation illustrates the importance of moisture recycling during the summer out here. If the mountains in southeast Arizona and northern Sonora had been active yesterday with heavy storms, then significant, cool moist outflows would have brought more moisture to lower elevations this morning. Further, it is not clear whether there will enough convection and/or cool advection and pressure rises with the upper-level trough over northwestern Mexico to trigger a low-level moisture surge. Note that this feature has also been mostly devoid of deep convection! A piece of it will shear northward across Arizona later today, but most of this feature will move off to the southwest over the Pacific.

Thus, we are left mostly at the mercy of small and mesoscale convection at higher elevations to bring enough moisture to low elevations to fuel thunderstorms. My outlook for here at the house is not very positive for storms today – barring a miraculous low-level surge by mid-afternoon – chances here are about zero for meaningful rain. Perhaps a few light middle level sprinkles and spits, but mostly hopes that things will come together better tomorrow.

STRANGE BREW

A number of unusual things have been going on during the past 24 hours.

First – minicane Andres appears to have totally dissipated during the night. The higher, cold cloud moved rapidly away to the west during late night/early morning and there appears not even to be a remnant low in the visible imagery. So, it appears that Andres might have helped move deeper moisture a bit north up the Gulf of California. But, if lower-level moisture increases dramatically tomorrow over south-central Arizona it will be due to the following factors.

Second – a pronounced upper-level cyclone is moving westward across central Mexico and will be a player in our weather as it appears that it will pass by at the 36-48 time frame, as it pulls northward ahead of the cutoff low that moves onshore during this period.

Third – the NWS models bring the Pacific, middle-latitude cutoff across the Great Basin, allowing the massive, middle-level anticyclone over the Plains to back westward over Arizona and new Mexico. However, the ECMWF continues to keep the anticyclone further east, allowing a moist flow to continue over the Southwest for a week or so.

Fourth – compare the TWC and ELP soundings this morning. The moist plume around the anticyclone has ELP in a deep, moist and unstable airmass. The light winds and CAPE in that sounding indicate a clear threat for flash floods. In contrast, TWC has a considerably less moist sounding with a deep residual boundary layer that extends almost to 500 mb. Moisture has been increasing slowly but the sounding still does not have CAPE. The Phoenix sounding is similar and its old boundary layer extends to just above 500 mb – the difference in old boundary layer heights at TWC and PHX lead to a deceptive difference of 4C in 500 mb temperature!

It appears that the evolution of all of the above may lead to a significant increase in moisture tonight and tomorrow over at least southeastern Arizona. So, the chance of storms will increase substantially tomorrow afternoon and evening. After that, it appears to be a watch and wait scenario.

Moisture increasing

Middle level moisture has been increasing over night and at sunrise this morning there were ACC and virga in all directions. Photo above taken at 6:10 am MST this morning looking toward southwest. TWC morning sounding indicates a small amount of CAPE present for parcels up around 550 to 600 mb. Next several days should be interesting! Bob

Interesting Longer Range Forecast Situation

It is the first day of summer and, since the southwest US thunderstorm season is approaching, I plan to begin posting commentary on the blog again, after a long period of little activity.

I felt that the longer-term forecasts this morning were interesting because the GFS and ECMWF appeared, to me, to be presenting quite different forecasts, especially after 72 to 96 hours. The GFS predicts a dry pattern with the 500 mb anticyclone (now over MS and AL) building westward to be over NM/AZ by 144 to 168 hours. The ECMWF, on the other hand, predicts another significant cutoff at 500 mb developing off southern CA, much like the past several events. So, the ECMWF has the baroclinc, westerly cutoff doing battle with the subtropical high during much of the forecast period. This leads to strong southerly flow and the ECMWF dramatically increases moisture over AZ/NM after 72 hours. I suspect that that the ECMWF may be the model to pay attention to this week – based just on persistence over the last 8 weeks or so.

It is interesting that the NWS forecast offices in the southwest US seem to have somewhat different interpretations of what the two models are indicating for the coming week, as per:

TUS
BOTH THE GFS AND ECMWF INDICATE A TROUGH OVER THE EASTERN PACIFIC MAKING ITS WAY ONSHORE INTO SRN CALIFORNIA LATE WEDNESDAY INTO THURSDAY. BY EARLY FRIDAY THE DIFFERENCES BETWEEN THE TWO MODELS BECOME QUITE DIFFERENT WITH THE GFS SHOWING A BAGGY TROUGH MOVING NORTH OF THE AREA...WHILE THE ECMWF SHOWS A CLOSED LOW STILL OVER S CENTRAL CALIFORNIA. THUS...THE ECMWF IS MUCH WETTER THAN THE GFS.

ELP
MODELS IN GOOD AGREEMENT WITH UPPER RIDGE FINALLY EXTENDING WEST INTO CWA OVER NEXT 36 HOURS AS UPPER TROF OVER WEST COAST LIFTS NORTH OF THE RIDGE. THE WEST COAST TRO REFORMS TOMORROW AFTERNOON AND MAY CHANNEL ADDITIONAL MOISTURE INTO SOUTHERN PORTIONS OF CWA AND TEMPORARILY REDUCE CAP.

PHX
ECMWF/GFS ARE IN VERY GOOD AGREEMENT WITH RESPECT TO THE PROGRESSION OF SYNOPTIC-SCALE FEATURES THIS WEEK.

ABQ
MODELS WERE IN REASONABLE AGREEMENT INTO THURSDAY WITH REGARD TO THE POSITION OF THE RIDGE AND WHERE THE BEST MOISTURE WILL SETUP BUT THE GFS AND ECMWF CONTINUE TO DIVERGE SIGNIFICANTLY BY LATER THURSDAY AND INTO THE WEEKEND.

FLG
INCREASING MOISTURE FOR THE REMAINDER OF THE WEEK. HIGH PRESSURE OVER TEXAS WILL STRENGTHEN AND PUSH WESTWARD...WHILE A LOW PRESSURE SYSTEM CUTS OFF WEST OF CALIFORNIA. THIS WILL OPEN THE DOOR FOR A STEADY AND GRADUAL MOISTURE INCREASE

So, we can look forward to a week of interesting changes, whatever they will actually prove to be, and can place our bets with our individual, long-term model of preference.

Bob

Very strong, local temperature gradients this morning

Had a very interesting walk this morning.

When I left the house at 5:40 am the temp in the back yard was42F. It was distinctly cooler as I walked down into the slightly lower elevations along the Rillito Wash. It was calm during the first half of the walk.

As I headed back up hill away from the wash I passed through a very sharp temperature gradient (micro or meso scale warm front). I estimate that the temperature jumped from about 45F to ~65F within about 10 to 20 feet. There were the lightest of winds stirring about at this "warm front."

As I progressed on back toward the house the wind speeds were gradually increasing, and the wind was about 15 kt and gusty when I reached the house around 6:40 am. The temperature on my return was 60F.

I note that the official NWS low temp at the airport appears to have been 56F just after midnight this morning.

Also of interest is that the low here yesterday morning (Sunday April 5th) was 32F - this may likely be the last reading at or below freezing for the 2008/2009 cool season here at house.

Interesting Event on Tap for Oklahoma

It looks like central Oklahoma is in for a shot of winter weather later this week and into Saturday. It will be interesting to see how much snow eventually falls - assuming the progged thicknesses are close - and how cold it will get after the precip event ends. Note that a large area of CO, NM (except NE corner), KS, TX Panhandle, and OK is already under a winter storm watch.

Over here in AZ we're looking at more wind and dust, which is par for course this time of year!

Roger in Oklahoma said:

Here in Okie-land, we got somewhat early growth. The dogwoods are done blooming and are leafed out, Jane magnolias and Bradford pears have peaked, the redbuds are in peak glory, and our wisteria is wafting wondrous scents all over our front yard. Let's hope against a late hard freeze. Tucson isn't very far behind Norman on rainfall so far:

http://www.stormeyes.org/tornado/raingage.htm

A Few Weather Notes - Mar 24 09

Probably of note - low here this morning (Tuesday March 24th 2009) was31F. First morning at or below freezing since February 21st.

I seem to be seeing lots of things growing and in bloom very early this spring!

On two days last week, the daily temp range here at house was over 50F - assumingthat high was similar to the airport high.

Precip for year

Jan 0.93"

Feb 0.87"

Mar 0.21" to date

Pretty wild blizzard in Black Hills last night and today - well forecasted by the models far in advance and handled very well by Rapid City NWS office.

Bad sounding data 12Z 24 Jan 2009

There is a severe superadiabatic layer aloft in this morning’s TWC sounding due to wetbulbing when the wetted sensor moved into a dry layer aloft. This transition was just below 700 mb and the “observed” 700 mb temperature is at least 5C too cold. See figures.

Model Comment from Art Douglas

I agree with your comments on the GFS and ECMWF tendencies over the past two years. I would add that in major pattern changes the ECMWF seems to do a better job in capturing that pattern change before the GFS finally switches. It appears now that the deep trof in the East will soon be replaced by a broad ridge in the Southeast. This pattern change is connected to the retrograding ridge in the Northwest that will be replaced by broad troughing along the Pacific Northwest Coast.

Until Sunday, the GFS was the model that was holding on to a very cold East while the ECMWF was starting to show the reversal with the building heights in the Southeast.Then the 12Z GFS on Sunday looked like last night's 0Z GFS run. Both runs had deep closed lows off California and a building ridge in the Southeast third of the country. This morning's new 12Z GFS has a closed low near Point Conception. As you point out the ECMWF has not been leaning this direction with a coastal system............but it suddenly changed last night with a deep trough down the California coast with similar 552 HTS near Point Conception (but not a closed low in any of the ECMWF ensembles). I bet the 12Z ECMWF will have some members with a closed low.

The current 12Z GFS and older 0Z ECMWF both have >0.50" in southeast AZ for the next 5 days and almost 1" on the Rim northwest of Phoenix. So the models are now converging and this time the GFS is the bold model per the pattern change. What happens on the plains is still a crap shoot given how far out it is.

Performance of the GFS versus the ECMWF

AJ from the NWS has suggested that it might be useful to start a thread on the blog focused on the mid-range performance of the GFS in comparison to that of the ECMWF. So this post is in response to his request.

First, some qualifiers:

I am not a model expert and all of my comments result from subjective appraisal of the various forecasts. I have not attempted to keep any kind of quantitative verifications, and the degree to which I examine the model forecasts at 3 to 7 days depends upon my level of interest and time available. Thus, my inputs are purely informal. I do not have access either to the ECMWF quantitative precipitation forecasts at this time, nor to many of the products from the GFS that are available at NWS offices. I tend to examine products at the NCEP web page and at the PSU electronic wall. I usually examine the 00Z runs, since sometimes the GFS goes into a flip-flop mode where the forecasts are quite different at 12 GMT than at 00Z GMT – I never bother to examine the runs at the 6-hour off times. I usually look most closely at the model forecasts over the Southwest and am thus regionally biased. All of that said, I note the following:

During this winter, and especially last winter, the mid-range ECMWF has seemed to catch important systems, and moisture influxes, better than the GFS. This has been a distinct enough difference that I routinely examine the ECMWF out to 168 hours before I check the GFS forecasts. I have noticed this winter that the GFS operational run is often quite similar to the ECMWF operational run (I don’t have access to, or know where, to examine the ECMWF ensemble members). However, the runs from last night at 00 GMT on January 21, 2009 are VERY different. Thus, today is a good day to try to start a new blog thread.

Note that at 168 hours from last evening (valid time 00 GMT on January 28th) the GFS indicates a quite cold cutoff west of southern California with a distinct 500 mb ridge over western Canada.. The GFS indicates significant precip over much of the West and Southwest and does not indicate precip over the central and northern Plains. On the other hand, the ECMWF indicates the two most important short-waves to be over Colorado and western Canada, with trailing vorticity across southern California into the east Pacific. The ECMWF indicates a frontal like band of precip across the Southwest. But the ECMWF forecasts an intense lee low and strong baroclinic zone over the Plains. Indeed the ECMWF indicates that near blizzard conditions would be impacting the central and high Plains at 168 hours.

I suspect that when the ECMWF performs better than the GFS that it is because its initialization over the Pacific, and also at low latitudes, is capturing features of key importance more accurately. This is sometimes especially noticeable with subtropical features and moisture fields. I think that it is well known that the GFS tends to be too dry over the Southwest.

I have also noticed that if the GFS ensemble members come into sync and consistently forecast precip over southeast Arizona in 10 to 12 of the members, then precip is almost certain to occur. This is true even at low elevations (the 00Z run indicates precip over SE Arizona in only 5 of the 12 members at 168 hours). Note that I have seen a couple of cases during the past two winters where the GFS forecasts were better than those of the ECMWF, but my subjective conclusion remains that I should examine the ECMWF first and then consider and contrast the other models.

What do readers think?

Happy New Year !

The blog has been a bit quiet lately, but we do have some news:

MADWEATHER has been listed as one of the 100 Best Blogs for Earth Science Scholars !!

See: http://www.bachelorsdegreeonline.com/blog/2008/100-best-blogs-for-earth-science-scholars/

Thanks to all of our blog readers and contributors!

Continuing Problems with RRS Data

All,

FYI - I have posted an article

"Strongly Superadiabatic Lapse Rates Aloft at Six Upper-Air Sounding Sites"
coauthored with Barry Schwartz at:

http://www.madweather.com/

We have examined data for two years of RRS soundings and compared with data from earlier sondes. This quantitative comparison indicates a very serious decline in the quality of the upper-air data is occurring because of the use of the new Sippican GPS microsondes by the NWS.

Response to AJ-NWS

Response to AJ of NWS - see AJ's comment on the previous post.

AJ makes a very good point here and one that serves to emphasize how difficult the forecast challenge is for the coming 84 hours. The three principal models each have different solutions, and we have little in the way of observational data to help evaluate the model initializations, since the key features analyzed by the models are within a great data void.

First, if one looks at the NAM, the GFS, and the ECMWF model runs from this morning – which I hadn’t when I wrote the original blurb – it is clear that each of the three models has somewhat different solutions for the initial conditions.

As per at 500mb:

The GFS analyzes an IT from south of GoC into north central MX where it connects with a trailing trough from the S/W over the central Missouri River Basin.

The ECMWF has this feature analyzed further north, extending from the south central GoC to SE Kansas.

The NAM is similar to the ECMWF except that it has several additional vorticity maxima further south and southeast which neither of the global models have.

We do know that such a feature is present and that at 12Z this morning it extended from Nebraska south-southwestward entering Mexico in the western Big Bend country.

Each model goes it own way in the forecast fields. The most important issue relates to whether or not there is a feature in the actual atmosphere that is going to spinup into a tropical system off Baja. Only the NAM indicates this evolution. The NAM solution would result in a very deep intrusion of subtropical moisture into the Southwest. At this time we mostly know that there has been ongoing convection in the regions where the NAM forecasts tropical development.

Both the GFS and ECMWF strengthen the inverted trough over north central Mexico and forecast this as the main feature that affects southern Arizona on Saturday and Sunday. The GFS stalls this feature over north central Mexico, while the ECMWF is more aggressive and keeps it further north and moving westward. The wind shear profile forecast on Sunday by the GFS is not nearly as favorable for organized storms (assuming that the key ingredients of moisture and CAPE have moved/developed north of the border). The ECMWF is probably in between the two other models wrt wind shear.

Current IR and water vapor satellite imagery indicate that the feature over north central Mexico has a clear circulation now and that it is moving westward. Significant convection is developing ahead of this feature over the Sierra Madre Occidental.

So where does all this lead? The forecast situation appears even more complicated than what I originally wrote. The most likely scenario for the next 84 hours is not at all clear at this time, and the evolving situation merits careful monitoring.

Challenging Forecast for the Weekend - Aug 23 and 24 2008

It appears that the large-scale setting here in the Southwest will be changing rapidly during the coming three days as very warm air in middle levels pushes into the Great Basin. Note the very warm 500 mb temperatures of only -4C at Medford OR and -3C at Desert Rock NV this morning. This warm intrusion builds the anticyclone back to our north and helps setup a more typical late summer flow regime.

Pressures have fallen and are quite low over the interior Southwest and may drop another couple of mb over the next 36 hours. There is also a weak inverted trough over the lower end of the GoC that has widespread convection associated with it. As this first disturbance shifts westward, there should be a low-level surge of moisture back into the lower Colorado River Basin. This moisture surge could begin as early as morning tomorrow but should be quite pronounced by mid-day Saturday.

The NAM forecasts that a tropical storm will develop just southwest of the tip of Baja and this feature, if it materializes, would deepen the moisture inflow to Arizona on Sunday and Monday. The NAM also forecasts very favorable wind shear profiles for organized convective storms in southeastern AZ both on Saturday and Sunday afternoons. Thus, both days could be very active if there is CAPE available.

It appears that the crucial aspect of the weekend synoptic setting will the temperatures in the middle levels. If the very warm air to the north and northwest spreads over southern Arizona and northern Mexico there would be little CAPE to realize, and it would likely be fighting an inversion aloft. However, if the easterly flow that develops at 500 mb has a fetch from the central and southern Plains by Saturday afternoon, the 500 mb temperatures would be much cooler and supportive of storms.

I think that the more favorable situation will evolve and, depending on the details, either Saturday or Sunday afternoon and evening should be quite active with strong and organized storms.

Slide shows re Severe Storm of 13 August 2008

Still bringing the new PC online, so none of the photos I took of damage produced by the early nigttime storm of Wednesday August 13th have been posted in the gallery. However, each of the Tucson newspapers have slide shows attached to their online articles about the storm.

http://www.azstarnet.com/sn/hourlyupdate/252838.php

http://www.tucsoncitizen.com/ss/local/93782.php

Computer Problems

I have been struggling with a failing PC here at the house and have been just able to get online every once in awhile. Thus, everything I usually do is to some extent on hold. We are going to replace this PC, but I may be out of touch for much of the next week or two, until a new computer is up and functional here. Bob

"When it rains it usually pours, but sometimes it just spits."

Rex Block
Private Investigator
Forensic Meteorologist

Sunday Morning Postmortem

Well my guess for yesterday afternoon was about as bad as I can do. Obviously the negatives dominated the local area around Tucson - only 7 of the 91 Alert gauges had rain yesterday, and the highest amount was 0.59 way down south at Tubac.

So what went wrong - I think that it was mainly related to the dry air in the upper-troposphere curling across southeast Arizona and keeping there from being much activity to the east - as per the WRF forecast. Although there were more storms to the east than the WRF indicated, they were not widespread and didn't produce any significant, organized outflows. With the GoC surge and increasing low-level moisture, the Tucson sounding at 00Z yesterday afternoon had substantial CAPE, but needed mesoscale convergence to kick it loose. That didn't happen.

As for today - moisture is way up as expected and there is substantial CAPE at both TUS and PHX this morning. El Paso is fairly stable so we have to assume that the air over the southeastern mountains is somewhat like the Tucson sounding. Morning wind shear from middle to upper levels is unidirectional but the NAM indicates that the wind profiles may improve by evening. Mainly a shear zone affecting southeast Arizona today and with no data from the south, it is hard to have much confidence in the model predicted winds aloft. So, there will be a lot of small and mesoscale interactions driving the evolution of storms today - good potential for more severe across all of southern Arizona and Phoenix could get hit by a strong, severe storm event. The chances are probably better for here at house today, but, even though it's not a binary call like yesterday, the shear profile could throw anvils over this part of town. So it's wait and see, as per many to most storm days down here.

The other wild card at play here is that there is a lot of strong morning storm activity out to the west of Tucson. If these storms continue to build produce early, cool outflows, that would complicate things greatly. I got a couple photos as sunrise showers moved by, producing an early morning rainbow. I'll post these to the blog later today.

Storm Outlook for Today

Visually spectacular storms yesterday evening - if anyone has photos for pasting on the blog, let me know.

Hot boundary layer temps and pocket of cooler 500 mb air, plus slight increase in moisture allowed storms, particularly at higher elevations, to overcome the strong inversion near 400 mb. Rain reported at 23 of the 91 Alert gauges in eastern Pima County - again mostly in mountains and foothills - the 1.50" at Agua Calienta Park seems an outlier, but there was spectacular lightning off that way. One wind damage report out at Pinal Airpark. Afternoon cells did not seem to have much in the way of precip shafts but then things obviously changed before dark.

Here at house - lightning, thunder and brief spit of rain shortly after 9 pm.

Situation today is very difficult with a number of competing plus and minuses.

Negatives first:

Very dry air to east in NM

Morning soundings continue with marginal IPW and boundary layer moisture.

Best difluence ahead of approaching upper-level, inverted trough appears to remain south of border.

Upper-level winds weak as we remain near the center of upper anticyclone.

Cool pocket at 500 mb has moved on to our west and northwest.

Pluses:

Nice push of subtropical moisture occurring into lower Colorado Basin, with some signature in PHX am sounding and Yuma VAD showing the influx to be about 4,000 ft deep. GPS IPW shows nice increases at the stations around the northern GoC.

Outflows from MCS over Mexico last night have pushed Td up across all of southern AZ and helped the GoC surge along.

Tropical low spinning off Baja in good location to keep low-level moisture flow going for a couple of days.

Very nice steering winds for storms that will tend to leave anvils to rear of strong cells.

Approaching inverted trough that extends down to 700 mb.

Summary - Looks good for strong storms with likely tropical squall line organization and somesevere storms and heavier rains, but today or tomorrow? I think things will come together today better than one might expect and that afternoon and evening should have strong storms - tomorrow will of course be highly affected by what does or does not happen during the next 12 hours. Chance of rain here at house probably at least 50% this evening.

Art Douglas Photos

Art has sent some digital photos from southeast Arizona - four of these have been posted on the Blog Gallery of weather images at www.madweather.com

Art's photos can be viewed directly at

http://www.squidinkbooks.com/madweather/photos-art-douglas.htm

Today's Weather - Southeast Arizona

Have been off-line for last two days due to dsl problems. So, it was the nice cool mornings that told me I shouldn't have doubted the NWS models and forecasts in keeping a dryout over Arizona for most of this week.

This morning there are, however, some indications of changes underway that will bring storms back into this part of the state. This morning there were quite a few ACC drifting around beneath the cirrus at sunrise. Since there has been no NWS sounding taken at TWC the last two sounding times, I have to guess about what a sounding here would look like this morning. There does appear to be some increase in east-northeasterly winds around 500 mb, along with some cooler temps advecting over southeastern Arizona today. Deep, subtropical moisture remains south of Hermosilla, but hot surface temps, along with the cooler middle level temps indicate that high-based storms should return to some of the sky island mountains of southeast Arizona late today, producing some lightning and gusty outflows.

The widespread convective activity over the southern half of GoC, coupled with falling pressures in the lower Colorado Basin, as well as the 500 mb wave moving slowly westward across the lower GoC all are good indicators that a northward push of the subtropical air is imminent. My guess is that we should see a push of low-level moisture into southwest and south central Arizona within 24 to 48 hours, followed by increasing storm activity for the next few days.

MORE BAD SOUNDING DATA AT TUCSON

I have just been perusing the morning sounding data and find that the TWC 1200Z sounding for today - Monday 28 July 2008 - poses a very substantial forecasting dilemma.

The sounding indicates IPW of 1.65" and the SPC analysis of this sounding indicates a forecast CAPE this afternoon of 1180 J/Kg. However, the GPS IPW from FSL indicates that precipitable water is probably between 1.3 to 1.4" - the difference between the sounding value and the GPS value being more than 0.25" - a huge difference and one that could seriously affect the convective forecast. See:

http://www.rap.ucar.edu/weather/upper/twc.gif

Note that the Td increases substantially between the surface value and the first level of sonde data - this aspect of the TWC soundings has been noted off and on - particularly on calm mornings - for the past several weeks. The Td values from the sonde then decrease nearly linearly to 715 mb, even though the sonde was passing through two elevated, residual boundary layers. The Td trace does not appear to be physically realistic and is probably too wet in each of the residual layers. Thus, I conclude that the Td data are bad and that the atmospere's dewpoint structure is quite different than that measured by the RRS sonde.

The reasons for the questionable data are not clear - but two possibilities come to mind - 1) local conditions on the roof of the NWS building may be affecting the first couple of data points and 2) the RRS sonde humidity sensor for this flight had a slow response time for Td and did not properly respond to Td changes below about 715 mb.

So, one is left wondering exactly what the local conditions might actually have been at the time of the sounding. So it goes.

Bad RRS Sonde Data Complicate Today's Forecast

Difficult forecast for today.

Low-level moisture has been sloshing around in different ways last night and this early morning, with decreases in the southeast from the east; increases in south central Arizona from the southeast; and increases in lower Colorado Basin due to weak surge which should continue and increase in strength and depth. Diurnal wind regime may return today in the Tucson area, which would increase the low-level moisture.

Entire forecast problem is acerbated by the TWC sounding which is apparently about 7.5 mm too wet this morning. I am guessing the bad data are at and below 850 mb and modifying the sounding accordingly. My estimated sounding for this afternoon has boundary layer well-mixed moisture at 10 g/kg and cloud bases at 650 mb. This gives moderate CAPE with only slight CIN above, assuming no further drying from east.

At 500 mb a weak inverted trof extends from the north end of GoC to SE Colorado, with some cooler air on the east side of this feature. At 200 mb a strong inverted trof extends from west of Albuquerque, south between El Paso and Tucson and into the vast Mexican data void. This setup gives the Tucson area good steering level flow this late afternoon, but little vertical shear. If storms organize along outflows, they could move westward faster than their anvils.

NAM model indicates better wind profiles tomorrow. Thus, good potential for organized and some severe storms either this afternoon or tomorrow, with the answer hiding in the devilish, smaller-scale details.

Severe weather pattern setting up last three days of week

Note that we've posted a weekend summary and some recent photos on the madweather web page, with links posted on the blog this morning.

Conditions remain very moist this morning; however, the TWC sounding is about 5mm too high in IPW according to the FSL comparison site. The 12Z sounding is quite strange, exhibiting the off-the-surface moist spike that Mike Leuthold pointed out about a week ago. Many of the 12Z soundings for last several weeks show this same artifact - particularly on calm mornings. This morning's sounding exhibits an adiabatic layer off the surface and then a sharp inversion to about 890 mb. This same layer has the strange Td structures. These data in lowest levels probably reflect the local conditions on the roof of the NWS building, and the moisture spike may result from similar contamination.

Regardless, moist and unstable and a calm troposphere again this morning. Only 11 of the Pima County Alert gauges had precip yesterday - making it the driest day since last Friday - with the significant amounts being on the mountains. The amount of anvil that the early mountain storms produced was truly amazing, but of course left all the lower elevations under thick anvil for much of the afternoon. Looks like anvils will tend to spread toward south and southwest today also.
Upper-level difluence increases this afternoon and evening as the inverted upper trof approaches. This feature directly affects southeastern Arizona tomorrow afternoon and steering level winds finally pick up. The 500 mb temperatures with this feature are -8 to -9C, i.e., very much cooler than have been observed at TWC for many days!

The best vertical shear for organized, propagating MCSs is forecast by the NAM on Thursday afternoon/evening as the winds at high levels - 200 mb - turn to south-southwest as remnants of Dolly approach the Big Bend. Wind shear predicted by the NAM remains very favorable on Friday afternoon. Very difficult to call which day will bring the most intense storms to southeast Arizona for rest of week, since local and small scale features and the previous day's events will be playing a big role each day. But it will be very interesting to observe what actually evolves.

Weather Summary for Past Weekend

We've posted a summary of the weather observed over this past weekend directly on the web page.

http://www.madweather.com/

It can be found under BLOG IMAGE GALLERY Weather Summary for July 18-20

We've also added some other July storm photos here, including lightning photos from near El Paso. these were provided by Mike Hardiman.

Weather Summary Last Three Days - July 18 through 20

Or - this is a direct link to the summary and photos.

Madweather post: Weather Summary Last Three Days - July 18 through 20

CURRENT WEATHER, MONDAY JULY 21, 2008

This morning conditions over most of Arizona remain very moist and the TWC morning sounding (Fig. 1 - link below) indicates a subtropical air mass with just over 50 mm of IPW. Although there is abundant CAPE, the winds aloft are light and variable through most of the troposphere. Thus, the situation is much like yesterday when there were many storms which remained mostly over higher elevations. The large subtropical anticyclone at 500 mb has three distinct sub-centers. The main one is over Arkansas with weaker centers in the west over southeastern Arizona and southwestern Wyoming (see Fig. 2).

The most interesting aspects of this morning's charts and the model forecasts relate to what will occur on Wednesday through Friday. There is a strong upper-tropospheric shear zone at 200 mb from somewhere near the southern end of the Gulf of California that extends east-northeast through the Mexican data void, and then across southeast Texas and southern Arkansas. The NAM initializes this feature a bit to the north and weaker than it appears to be. The NAM forecasts the west end of this feature to become a distinct upper-cyclone that moves westward across northern Mexico on Wednesday and Thursday. As this occurs, the 500 mb steering flow becomes east-northeast. The flow at 200 mb becomes more diffluent, initially from the east-northeast on Wednesday and then from the southeast on Thursday. Thus, a more favorable shear profile returns for propagating and organized storms.

It then appears that the remnants of TS/Hurricane Dolly (see Fig. 3) will affect southern Arizona on Friday and perhaps Saturday. Currently, the models and NHC forecast Dolly to follow a track similar to that of Claudette during the period July 8-17th in 2003. All-in-all it should be an interesting weather week.

Figure 1 Figure 2 Figure 3

Weather Summary - 30 June Through this Morning

The last seven days have been quite amazing here in southeastern Arizona. There have been thunderstorms somewhere in the Tucson metro area every day except for the 30th, which was suppressed due to strong, downslope east winds.

Yesterday was the day with the most widespread rains. A large are of heavy cloud at sunrise acted to suppress local storm development. But shortly after dark outflow winds converged over Tucson, helped by two weak short waves - one from the southeast and one from the northwest - triggering a large MCS. Every one of the Flood Districts 91 gauges reported measurable rainfall except for three - which I suspect may be out of order. Largest accumulation was 2.60 at White Tail on the Catalinas. Here at the house we had 0.60".

Today the two middle-level waves continue to interact and the atmosphere is very wet with high IPW amounts. The widespread rains will mean a shallow boundary layer later today that will need strong outflows into lower elevations if storms are to develop away from the mountains. The longer range forecasts continue with very wet forecasts out past 7 days as both depression Five-E and an upper cyclone over eastern Mexico move slowly this way and continue the flow of subtropical moisture into the Southwest US.

Some summaries for the past seven days:

Douglas Tstms on the 1st, 3rd, 5th, and 6th total rainfall 0.17"

Art Douglas reports storms and rain at Ash Canyon (just south of Sierra Vista)
on the 2nd through the 5th (and probably yesterday also) with rainfall of 1.00"

Nogales: Tstms every day with total rainfall 1.31"

Tucson (TUS) Tstms on 1st, 3rd, 4th, 5th, and 6th total rainfall 0.45"

Here at house Tstms on 1st, 3rd, 4th, 5th, and 6th total rainfall 1.39"

Phoenix (PHX) Tstms on the 3rd and 4th total rainfall only a Trace

Note that Phoenix has had high temps of over 105F every day of this period and that 3 days were over 110F. While temps were over 100F in the afternoons the dewpoints were often in the middle 50s to low 60s. Thus, the heat stress and misery gradient between Tucson and Phoenix this last week has been very strong, probably maximizing between Picacho Peak and Casa Grande.

Spitting Rain

Someone asked me if my use of "spitting rain" was a technical term and, if so, what does it mean?

Obviously, it's not very technical, but here is my attempt at a definition.

Subjective - if it is spitting rain, you can almost run between the drops.

More quantitative - if you observe spitting rain falling onto a porous surface, such as concrete or flagstone, you'll note the following. The drop splats and wet spots remain separate from one another while it is spitting rain. If the surface becomes completely wetted, then light rain, or heavier, has begun.

So that's it - not copyrighted; feel free to use.

Watch a video (Madweather's first attempt at doing this!)

Storms in Tucson on the Fourth of July

While the central and south parts of the state were very active yesterday with several severe storm reports, the nearby mountains here were suppressed relative to the day before. The boundary layerby late afternoon was only well-mixed in moisture up to 600 mb. This layer required substantial lift for its CAPE to be released.

A strong cluster of storms near Green Valley produced a deep outflow that was visible on the KEMX base scans. It passed TUS at 6:46 pm when winds shifted to the south with gusts to 38 mph. Thunderstorms were developing along this outflow as it moved north across the city. We had thunder and light to moderate rain here at house from about 7:00 to 7:40 pm with total rainfall of 0.35". The lightning was quite spectacular with CG bolts jumping out to the north of the cells through clear sky. Quite a dangerous situation.

Significant moisture remains in place but winds aloft over southeastern Arizona are becoming nearly light and variable in the NAM forecasts through midnight. My guess is that this afternoon's well-mixed, in moisture, boundary layer will have theta w of about 24C - a very favorable value for moderate CAPE and heavy storms. But the situation will probably be like yesterday and the air mass over the deserts will require a good kick from outflows from storms at higher elevations. Timing will depend on heating and how quickly storms develop over higher elevations. Also appears as if the northwestern half of state will have an active day.

Interesting Weather Continues in the Southwest

Weather Update - 8:00 am Friday July 4, 2008

Yesterday was a very active day with most reporting stations in southeast and south central reporting thunderstorms and wind gusts of 30 mph or greater. Douglas reported a gust to 75 mph, and others of note were: 53 at Mt. Hopkins RAWS, 45 at Scottsdale airport, and 44 at TUS. The Pima Flood Control District monitors rainfall at 91 sites in eastern Pima County and 56 of these sites reported measurable rain for the 24 hours ending at 6 am this morning. Notable amounts: 4.61" at Manning Camp in the Rincons (this is from a RAWS site and may be suspect) and 1.77" at Oracle Ranger Station. The most rain reported in the main part of the City was 0.47" at Pantano and Houghton. Of the 18 City gauges only 6 reported measurable rain, showing that the higher elevations did much better. Here at the house we had lots of lightning and thunder, several outflows and a couple of brief spits of rain, amounting to a trace. But the cool outflows and strong smell of rain made for a great evening.

This morning the moisture contents over southern Arizona have continued to increase. The TWC sounding is very moist and indicates the most CAPE present for the season so far. The IPW products and surface observations show that the surge of GoC moisture which began midday on Wednesday has pushed north almost to Las Vegas. IPW at Tucson is 38 mm this morning and Phoenix has 41 mm.

Winds in the upper and lower troposphere are light and variable, but steering level winds from 400 to 600 mb are from the east-northeast at 15 to 30 kts. There are no synoptic features of note today, except for the moderate wind flow around the midlevel anticyclone and perhaps a bit of midlevel cool advection. Expect that it will be another active day across much of southern Arizona. With higher moisture and lower cloud bases, the threat of heavy rain is greater today and the possibility of severe downbursts remains significant. The increased CAPE will allow better propagation of mountain storms into the deserts during the afternoon and evening.

So, another active day likely with lightning fireworks for the Fourth.

Weather Discussion for Thursday July 3rd 2008

Prepared Thursday July 3rd 8:30 am

Low-level moisture has continued to push into the lower elevations of all of southern Arizona during the night. Moisture increases and southeasterly winds are most spectacular over the lower Colorado River basin as per Yuma surface observations, the KYUX Doppler velocities (See Figure 1 and Figure 2) and the GOES IPW (Figure 3). Winds at 1500 UTC this morning are gusting 20 to 30 kts at Yuma and the dewpoint has risen into the lower 70s. The VAD shown in Figure 2 indicates that the surge of GoC air may bextend up to 4,000 ft AGL.

The Tucson 1200 UTC sounding this morning shows a slight increase of low-level moisture and is a bit dry relative to GPS IPW. There is a very deep residual boundary layer from yesterday and some CAPE indicated over low elevations, with CAPE over the higher mountains likely to be quite substantial. This afternoon's CAPE at lower elevations will be determined by how the low level moisture is advected by low-level winds, any further increase in moisture, and also by any warming that might occur between 500 and 400 mb - so estimating desert CAPE is toughest aspect of this afternoon's forecast.

Steering winds are likely to be northeast to east at 20 to 25 kts around 0000 UTC, while upper-level winds will blow the anvils off to the southeast - an excellent shear configuration for severe thunderstorms in southeastern Arizona. With diurnal afternoon low-level winds from the west-northwest, the shear profile below 500 mb will be supportive of strong, mesoscale outflows.

The threat for severe macroburst winds today is high, and depending on how the CAPE evolves there may also be some heavy rains in lower elevations and possibly hail. Hail is quite likely in higher elevations.

All-in-all looks like a good setup for a significant thunderstorm day here in southeast Arizona and also in much of the Southwest. As is often the case here in southeast Arizona, the outlook for tomorrow will be strongly impacted by how convection evolves late today and tonight - the NAM indicates even more activity tomorrow but this could be impacted by strong outflows later today and tonight. An interesting 4th regardless.

Weather Discussion - 9:00 am Sunday June 29, 2008

There are many interesting things happening over the Southwest and so this discussion.

For the past week or so there have been daily thunderstorms over southeast, and sometimes central, Arizona. Moisture values and CAPE have generally remained marginal with IPW values of around 25 mm. Thursday afternoon (the 26th) IPW increased briefly above 30 mm and there was ample CAPE over lower elevations of southeast Arizona for severe storms and heavy rains to occur in the Tucson metro area. The street flooding here on the north side of town was quite impressive, even though at the house there was only 0.33" of rainfall. Temperatures in middle levels have remained quite cool through this period, with temps at 500 mb of -8 to -10 C, and thus there has been CAPE around even though moisture values were low.

On Thursday the high, subtropical values of IPW (>37.5 mm) had inched northward toward the end of the GoC and the borderlands. This morning the subtropical moisture has retreated southward and covers only about the southern third of the GoC.

This morning the Tucson sounding indicates that there will probably be CAPE present this afternoon at lower elevations in southeastern AZ. If we end up with 4 g/kg in the well-mixed boundary layer (BL) there will be slight CAPE, but it looks like the value could be 5 g/kg or even greater. Steering-level winds are easterly at about 20kt. There is a weak upper-level SW over New Mexico and the NAM forecasts part of this feature to move southwestward and interact with the northern end of a quite pronounced tropical wave. So the potential for storms appears enhanced today, especially given that 500 mb temperatures remain in the -8 to -10 C range across all of the southwest. There is also pronounced westward advection of higher moisture values across southern New Mexico. By afternoon there should be substantial moisture convergence over southeastern Arizona as the afternoon diurnal northwesterly winds butt into the easterly flow from New Mexico. Thus, there appears to be high potential for a significant storm day over southeastern AZ today, with severe macrobursts likely - given the high cloud bases and very hot subcloud BL.

In the longer term it finally appears that a wave of significance will move across the lower GoC. The models indicate substantial cool advection at 700 mb with the tropical wave that is now over Mexico and indicate significant storm activity likely in Sinaloa and southern Sonora - perhaps even moving out over the GoC. It would be nice to have some sounding observations over Mexico to help one evaluate the model forecasts, but all of northern Mexico has been without upper-air data for almost a month now. The evolution and movement of the wave, as predicted by the models, as well as the cool advection and rainfall would trigger a low-level surge of high moisture values into southern Arizona sometime between early morning on Tuesday and mid-day on Wednesday.

All in all, it looks like a number of very interesting days are on tap for us here in southeastern Arizona.

II. Problems With the TWC Soundings on 23 June 2008

Problems with the data from the RRS sondes are again starting to impact the analysis of the soundings taken at TWC and the forecasting of convection here in southeastern Arizona.

The FSL time series comparison of GPS IPW versus TWC IPW since the 19th of June indicates that 5 soundings were apparently too dry, while one sounding (1200 UTC 19 June) was very wet relative to GPS IPW. See Figure 1. Careful monitoring of the remotely sensed IPW continues to be the best way to make an initial assessment of how accurate a given TWC sounding might be.

The 00Z sounding last evening (see Figure 2) indicated a deep, well-mixed boundary layer extending up to 500 mb; however, the moisture structure was quite questionable, with very dry conditions off the surface and no recovery to a well-mixed value. This led to the "dry" sounding wrt IPW.

The 12Z sounding this morning (see Figure 3) indicates a very deep residual boundary layer, but the moisture structure is extremely erratic. The IPW values correspond well. Given the unrealistic physical nature of the Td data, I suspect that the agreement of the two IPW values is essentially a coincidence this morning. If the afternoon BL mixes toward 5 g/kg, then there is a small amount of CAPE present; however, if it mixes toward 4 g/kg then there is no CAPE present. Given the erratic Td data trace it is very hard to make a subjective forecast of the late afternoon sounding.

The Haboob of Saturday Evening June 21st 2008

This was probably the first significant event, for southeast Arizona, of the 2008 summer thunderstorm season. Widespread convection occurred over parts of southeast Arizona and particularly over southwest New Mexico and northern Mexico. See Figure 1.

High cloud bases and a very hot boundary layer led to an organized, mesoscale outflow that affected much of southeastern Arizona. Passage here in Tucson occurred about 4:30 pm local time. The outflow was well-depicted as a fine line on the KEMX reflectivity display see Figure 2.

Note that Douglas, Arizona, reported a severe convective gust of 51 kt at 3:32 pm local time after the haboob had moved passed. This severe storm event did not make it into SPC's list of wind events for the 21st.

We were returning to Tucson from Chicago and landed about 10:00 pm local time. The approach was very bumpy and winds were still gusty from the east to southeast. The air was heavily laden with dust, giving the 3/4 moon a very strange and dirty yellow-brown appearance.

REST OF MONTH LOOKS INTERESTING FOR SOUTHWEST

Both GFS and NAM model forecasts continue to be quite interesting for the Southwest.

Appears that there may be high-based, dry lightning storms over the mountains of far southeast AZ this weekend. Definitely not good, given the extreme dry conditions of last two and a half months. Only 0.09" of rain here at house since March 17th!

In the longer term, the GFS ensemble members keep a strong, middle-level anticyclone north Mexico/southern Plains, and then tend to shift it northward during last 10 days of month. Throw a tropical disturbance into this pattern and who knows what we might see down here.

I'm off to Wisconsin where it will be green and wet and probably muddy.

OVERVIEW of RRS SOUNDINGS 6 JUNE 2008

I have been involved in other things last few days. Have just taken a look at today's soundings and report the following:

0000 UTC soundings with superadiabatic layers aloft apparently due to wetbulbing:

UIL SLE BOI OTX FWD OAX SHV MSP TLH BMX APX MFL

ABR has an extreme super layer aloft but it is not due to wetbulbing. LBF flight missing.

12000 UTC soundings with superadiabatic layers aloft apparently due to wetbulbing:

UIL SLE ILX OTX DVN SGF

OUN sounding appears very strange for unknown reasons.

SUSPECT RRS DATA FOR 23 MAY 2008

Numerous data problems continue in the RRS soundings.

Overview of suspect data for 0000 UTC 23 May 2008:

Superadiabatic layer(s) aloft:

LBF UNR SLE TWC FWD LIX TLH LCH MFL BUF

Additionally - the LBF flight was incomplete; the MHX flight was missing all winds except that at the surface; the LIX flight also exhibited a warm spike and extremely noisey data; the JAN flight was terminated.

Overview of suspect data for 1200 UTC 23 May 2008:

Superadiabatic layer(s) aloft:

LBF UNR TWC FWD OUN TLH MHX DVN BMX BNA APX RNK

Additionally - the UNR and MFL flights exhibited extreme noise in the RH data and the bizarre TLH flight was terminated.

MANY SUSPECT SOUNDINGS THIS MORNING

While there were lots of bad or suspect soundings last evening, this morning's data appear quite bad. At least for the number of flights with obviously suspect layers. I guess this reflects the important weather systems affecting the continental US today - Thursday 22 May 2008.

Visually obvious problems appear in the sounding data as per:

Warm spikes at GGW RIW

Superadiabatic layers aloft at GJT GGW(3) SHV TOP OMA AMA JAN TLH MFL(2)

Suspect layer (Opposite of wet bulb superadiabatic) at UIL SLE MFR APX

Some of these are quite amazing. The sounding data can be easily viewed at Univ. of WY's upper air page:

http://weather.uwyo.edu/upperair/sounding.html

Note that two of the suspect soundings are from non RRS stations - TOP which flew into an MCS and MFR which showed a weak Op-Super layer from its VIZ instrument.

I call the strange layers "Op-Super" that occur when sonde exits cloud into drier and warmer air and T increases rapidly but RH stays at 100% for a while. This likely indicates a hygrister problem vs wet bulbing under same conditions which indicates a wetted thermister.

A Quick Look at This Morning's 1200 UTC Soundngs

Friday Morning 16 May 2008

I have had time to take a quick pass through the morning soundings.

Soundings having a super-adiabatic layer aloft include:

MAF BRO LIX TLH MHX GYX

Soundings having a warm spike aloft between 0 and -10C include:

GJT LIX IAD

Too busy today to take a careful look at any of these.

Super-adiabatic Layers This Morning

The following soundings exhibit elevated super-adiabatic layers this morning for the 1200 UTC flights:

AMA FWD BNA LBF LZK JAN LCH

The problem at LBF was due to an intense warm spike.

The too cool layers in several of these soundings cause computed CAPE to be inaccurate.

I cross-checked the NCAR RAP plots with those at Wyoming this morning, and all the above
problem soundings were similar at each web page.

LCH is the most bizarre sounding of the bunch. The instrument apparently was launched into
a thunderstorm or deep convection.

RE Flagstaff Sounding Previous Post

The bad sounding shown for Flagstaff was apparently due to the following:

Data were missing for for a short period.

Operator interpolated data for the missing period.

A saturated point was interpolated with T/Td spread shown as //

The NCAR Rap sounding decoder did not interpret the // correctly,
producing the very strange sounding on their web page.

The decoders at Wyoming and SPC plotted the data correctly.

Suspect Soundings - Two Recent Examples

The figures below show soundings from Flagstaff AZ yesterday morning at 1200 UTC and from Ft. Worth TX this morning at 1200 UTC. Both have suspect layers, but the cause of the problems are not obvious.

Figure 1 - KFGZ

This sounding indicates a very dry layer of almost 100 mb vertical extent just above 700 mb. It had been raining for several hours and at the time of release Flagstaff was reporting moderate to heavy snowfall. The snow continued for several hours after sounding time. The dry layer certainly does not seem physically realistic, given the steady precipitation event that was underway.


Figure 2 - KFWD

This morning's sounding at FWD indicates a strongly super-adiabatic lapse at about 710 mb. This excursion causes a layer that appears to be several degrees too cool from about 710 to 550 mb. The net result is that sounding analysis software routines would produce CAPE values that were likely too great. Since the sonde did not, apparently, rise into a very dry layer, the reason for the super-adiabatic layer aloft is not clear.

Both of these soundings may illustrate random instabilities within these two RSS sonde's internal electronics, but this is just a guess on my part.

Problem Soundings 0000 UTC May 9th

My quick look at the soundings last evening identified two RSS flights that exhibited strongly super-adiabatic lapse rates in shallow layers aloft. These soundings were taken at Birmingham, AL, and Sterling, VA.

Note that the RRS operational procedures indicate that layers such as these should be removed via manual editing by the operator, and provide instructions for how this should be done.

Figure 1 (00Z BMX)

The layer of interest here extends from about 630 mb to 610 mb. The sonde apparently had moisture on the thermistor, and perhaps on the hygristor. When the instrument exited a deep, cloudy layer it encountered very dry air aloft and evaporative cooling of the sensors probably produced the super-adiabatic layer.

Figure 2 (00Z IAD)

The layer of interest here is only about 10 mb deep and is located near 740 mb. The reason for this super-adiabatic layer is not obvious, since the entir atmosphere appears to be quite moist. The sounding apparently did not exit cloud into a very dry layer above. It is possible that the instrument was in a saturated updraft and exited the updraft suddenly. It is also possible that the hygristor did not respond adequately to a layer that was considerably drier than the data indicate.

During the next few months I'll be paying particular interest in identifying soundings in which bad data have complicated the diagnosis of CAPE or potentially caused forecasting difficulties.

If readers note soundings that seem to be candidates, as per above, for closer examination, please feel free to alert me to them. Thanks, Bob bob@squidinkbooks.com

BLOG will be active now for the spring/summer

I am beginning again to monitor the RRS Sippican sounding data, as I start preparing a formal paper. This paper will document the often poor, and physically bizarre, soundings produced by the Sippican radiosondes the NWS has switched to at most sites in the US.

Today's winning example of a strange sounding is that taken at Ft. Worth TX at 1200 UTC.

http://www.rap.ucar.edu/weather/upper/fwd.gif