Brief Summary Yesterday/Outlook Today

Yesterday was essentially a down day in most of southeast Arizona with some isolated, high base storms. There were 5 of 93 stations (foothills of Catalinas and Rincons) in the ALERT network which had very light amounts of rain during the late afternoon and none with rain during the night (0.08” at one station). A cell near Casa Grande produced a report of wind damage and dust blew in over Phoenix from the south, reducing visibility at Sky Harbor to as little as a quarter mile. The most intense storms of the day developed over the rugged terrain of the Tohono O’odham Nation during late morning. These intensified and move rapidly westward, apparently ahead of a S/W at 500 mb. These storms (see 2245z satellite image above) reached Yuma around 4 pm producing a serious dust storm, wind damage and measured gusts to 54 mph at the airport. Yuma also reported 0.10” of rain, so mud is probably splattered over everything out there this morning. I couldn’t find a good image to grab, but there are several videos of the event up on the internet.

An MCS that decayed over the central GoC may produce a shallow surge today, but it probably won’t be significant enough to change the thermodynamics much. This morning’s TWC sounding indicates that yesterday’s residual boundary layer has 6.5 g/kg mixing ratio. This value produces a lifted parcel that hits saturation at about 570 mb with theta-w of about 20.5C – really quite low for late July. Moistening during day could perhaps yield a low-elevation, lifted parcel with theta-w of 22C and a small wedge of CAPE between 500 and 300 mb.

Precipitable water values are around an inch to an inch and a quarter (a bit higher after the local moistening out around Yuma). Yesterday evening’s TWC sounding exhibited the common hot/dry problem of the RRS sondes and was about 0.3” too dry.

The 500 mb anticyclone is centered over the White Mountains and is progged to shift slightly southward toward Wilcox during the day. Thus, it appears that it will be another very hot day of isolated, high-based storms that will have excellent microburst/downburst potential. I will have to be watering some of the plants this evening – which again is not so typical in late July.

However, the S/W that produced the Yuma storms will likely bring some excitement to the mountains and interior of southern California.

Mike Hardiman Wrote Yesterday

Bob,

We had a similarly too-dry RRS sounding at EPZ on 00z 7/16. RAOB PW was 0.79 inches... GPS was at or slightly above 1 inch. AWIPS/D2D has a rudimentary sounding modification program. "Fixing" the boundary layer dewpoints, and smoothing out the mid-level noise only gave me about 0.88 inches PW, and sfc-based cape of about 100 J/Kg.Either way, the rather stable sounding belied the reality of the convective coverage and strength, which became quite strong especially just south of the border.

Mike Hardiman @ EPZ.

Rainfall Amounts Yesterday

I forgot to mention the rainfall produced by yesterday’s storms. First, 61 of the 93 Pima County ALERT network gauges caught rainfall, so coverage was way up from previous days. Most amounts were light, half an inch or less. The maximum amount I saw was 1.02” at a station in Oro Valley. Here at house we had 0.19” and winds were not particularly strong, estimated only 20 to 30 mph.

The strong north-northwest outflow that came around the east flanks of the Catalinas really flared-up the Guthrie fire and there was a spectacular, ground-hugging plume of smoke blowing off the fire. Unfortunately, I could not get a decent photo of it.

The photo above shows the storms on the west flanks of the Catalinas heading into Oro Valley.

Strong Storms Yesterday with Wind Damage

There was more widespread storm activity yesterday than on Thursday and the storms occurred in the late afternoon. There were numerous reports of wind gusts over 40 mph from Luke AFB south to Sells and east to the White Mountains. Safford had lots of wind damage and bad dust in the area and measured a gust to 63 mph. The Black Hills RAWS station measured a severe gust of 57 mph and Horse Camp RAWS and Casa Grande ASOS measured gusts of 54 mph. The ATMO rooftop anemometer had a gust to 75 mph. Yesterday’s storm setup was about as synoptically evident an event as occurs out here in the Southwest.

Today is more complicated. The PW trends have been down everywhere except out at Yuma, and as Mike Leuthold mentioned yesterday, the models forecast more drying this afternoon over southeast Arizona. The NAM gradually shifts the 500 mb anticyclone from western Utah toward the Four Corners by evening and then southward toward the Chirachuas tomorrow afternoon. Thus, the favorable wind shear environment for strong storms will continue through this evening but CAPE will be on the wane.

The TWC morning sounding is quite interesting. First, GPS PW values indicate that the sounding is too moist by about a tenth of an inch. There are two, deep residual boundary layers present – one from about 920 to 670 mb and the second from about 630 to around 450 mb. Thus, the entire lower half of the troposphere has a very strong temperature lapse rate. There were ACC floating around at sunrise, indicating the instability present at the top of second residual layer. So, it appears to me that the situation today favors very high-based storms that move westward from the mountains producing microburst/downbursts at lower elevations where it will be very hot.

Jim Toth Wrote

Yesterday afternoon, just after 4 PM (let's say 2310Z), I was around the Tucson mall, driving east. Glancing at the Catalinas and the Rincons, it occurred to me that the atmosphere looked different from previous afternoons, like it was primed for late action (at that moment I was thinking "well, possibly 2 or 3 AM"). It's not that I was expecting a trigger, or had given much thought to the likelihood. I think what struck me was that there were a few small thin towers sitting in the haze over the foothills, out away from the mountains. So I wasn't entirely surprised to hear the first rumblings around 9 PM. Later, looking at the NWS discussion, I was trying to reconcile the reported drier sounding with what my eyes had told me at about the same time.
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This afternoon the air is particularly hazy and/or smokey - there appears to be a fire burning on the east flanks of the Catalinas - I can see a smoke plume from the backyard. Wouldn't be surprising given the numerous lightning strikes last evening. Bob

Brief Outlook for Today - Friday July 17, 2009

I posted a long message below about yesterday – important event because bad RRS sounding clearly led the NWS astray on the short term forecast for the storms approaching the metro area.

As for today, it appears that most ingredients for a big severe storm day are, or will be by late afternoon, in place, except for the continuing and distressing shortage of low-level moisture. I can finagle a sounding modification that gives us similar CAPE to yesterday – perhaps a tad better.

The 500 mb anticyclone is over Arizona/Utah border and elongated SE to NW. Very good steering flow and shear profiles by afternoon. Cool middle level air coming around the 500 anticyclone. Not obvious exactly where weak 500 S/W might be, but NAM initialization appears a bit suspect, acerbated by missing winds at Guaymas. The weak inverted trough at 700 mb is clearly east of here and visible satellite loop indicates 500 mb S/W may be also.

One possible complication is the large mass of cloud and some convection over northern Mexico and borderlands of southeast Arizona. This could limit heating to some degree and possibly get too much convection going too early. But it should be another interesting day.

Bad RRS Data Impacts Short Term Forecasts

Postmortem on Last Evening

First – the event last evening illustrates the problems forecasters can get into with bad data from the RRS soundings. From the 8:30 pm TUS NWS Forecast Discussion:

THUNDERSTORMS THATFIRED NEAR THE MOGOLLON RIM/WHITE MOUNTAINS HAVE PROPELLED ANOUTFLOW BOUNDARY SOUTHWESTWARD...WITH NEW STORMS FIRING ALONG ITACROSS GRAHAM AND COCHISE COUNTIES. THESE STORMS HAVE REMAINED BELOWSEVERE LIMITS...ALTHOUGH CERTAINLY HAVE SEEN PLENTY OF LIGHTNING ANDOUTFLOW WINDS OF 40-45 MPH WITH THE STRONGEST STORMS...ALONG WITHAREAS OF BLOWING DUST. DECENT COMPLEX OF STORMS IN WESTERN COCHISECOUNTY IS PUSHING OUTFLOW INTO THE TUCSON METRO AREA/EASTERN PIMACOUNTY THIS EVENING. RUC SUGGESTS THIS COMPLEX WILL STAY PRIMARILYSOUTHEAST OF TUCSON. 00Z KTWC SOUNDING SOMEWHAT DRIER WITH A PW DOWN TO NEAR ONE INCH.

However Mike Leuthold wrote last evening about the apparently benign TWC 17 July 00Z sounding (see SPC plot and diagnostics above):

"You have to 'fix' it. I used nsharp to bring up the PW to near the GPS value. Then, I saw about 500J/Kg ML CAPE and about 800 surface based CAPE."

The sounding last evening was too dry, as is often the case with RRS sonde data, and GPS indicated actual precipitable water about 1.3 inches – a critical flaw in the data since the missing moisture was obviously in the boundary layer, affecting CAPE and the local evolution of the spectacular lightning storms. Pat Holbrook had correctly called for an “up” day or early evening yesterday morning.

The storms of interest for Tucson developed late afternoon from the flanks of Mt. Graham southward. The storms moved south and west producing two very distinct outflows that moved southwestward across all of southeast Arizona. One area of storms moved southward into Mexico as a long-lived MCS and a second area broke to the west along I-10 with the northern outflow. These storms moved into Tucson metro area around 9 pm producing frequent, vivid lightning and areas of brief TRW+. This cluster of storms dissipated rapidly after 10 pm. As the outflow moved across the metro area it apparently triggered new development along the slopes of the Catalinas, so that visually the storms seemed to be moving northward, even as radar indicated they were moving to the southwest. Quite a show!

As for rainfall, 32 of the 93 ALERT gauges had measurable rainfall after 7 pm while none had any rainfall during the day. Maximum amount was 0.79” at Rancho del Lago near Vail, on the flanks of the Rincons. Here at house we had 0.38” which was most welcome; the lightning was a better show than the Fourth of July!

Mexican MCSs and Misc.

There were strong MCSs in northern Mexico again last night with outflows moving into southern Arizona. The satellite image above shows that there were again MCSs on either side of the Sierra Madre Occidental divide – I’m not sure how unusual this might be?

No stations in the Pima County ALERT network reported rain yesterday afternoon and only 12 of 93 stations had rain on Tuesday.

Maybe I’m not looking hard enough, but I’m not finding much in the model progs to get excited about – is anyone else?

Summary of first 15 days of July here at house:

4 days with measurable rain (7 in 2008)

I only heard thunder on 5 days (10 days in 2008)

Rain total 1.52” (but I know that most areas of metro area have had much more!)
(2.70” in 2008)

So, here at house quite a down July so far compared to last year – what we get for living in the “Rillito Dry Slot!”

Interesting Evening in Phoenix

While southeast Arizona was almost totally suppressed yesterday by the lingering impacts from the Sonoran MCSs, storms did develop over the Rim country. Some storms on the north side of a weak, midlevel 500 mb trough propagated into and then across the Phoenix area. Although there were a few spots with light rain, the main impact was a duster with 3o to 40 mph outflow winds (the outflow boundary is quite clear to the west of Phoenix on the 0600Z radar image above).

The weak shortwave trough remains between Phoenix and Tucson this morning and moves little during the day. The upper-level shortwave that’s come north along the Baja Pacific coast shears out quickly to the east today. Precipitable water values remain moderate with values over Arizona of 3.1 (TUS) to 4.1 (PHX) cm. More moist and unstable subtropical air remains just south of the border (Guaymas PW this morning 4.7 cm). The Phoenix sounding indicates that there’ll be some afternoon CAPE, at least on the north side of trough. Higher elevations should continue to have highest CAPE this afternoon.

With light winds below anvil level and convective cloud bases around 600 mb, storms will move slowly and produce some strong dusty outflows again.

DOUBLE MCVs

Mike Hardiman wrote:

Hey Bob,

Indeed a very impressive MCS last night over the Sierra Madres. There were actually two systems...the one that developed over NE Sonora, and another intense, but more compact MCS over NW Chihuahua near Nuevo Casas Grandes and Janos – minus 78C tops on both systems at their peak per IR.. NCG reported just under an inch of rain per SMN:

http://smn.cna.gob.mx/productos/map-lluv/h2o.html

These systems actually left us with twin MCVs over southeastern Arizona. As of this afternoon (4pm MDT), convection is firing up along an arc from near Show Low, AZ to just north of Deming, NM. Surface obs suggest these are developing on the edge of the low level moist pool associated with the MCS leftovers, and aided by local terrain.

I'll email you a couple screen grabs, and feel free to post them.

-Mike Hardiman
(NWS EPZ)

Nothing is Easy

2100 UTC graphic from Mike Hardiman

Very interesting evolution of things.Precipitable water has fallen back to yesterday's levels; temps are cooler and dewpoints slightly higherexcept at Yuma and pressures are 4 to 5 mb higher than 24 hours ago:

Tucson T -5F Td +3F P +4 mb
Phoenix T -6F Td +7F P +5 mb
Nogales T -4F Td +0F P +4 mb
Douglas T -1F Td +1F P +3.5 mb
Yuma T -5F Td +29F P +4 mb

Thus, it looks like we have been smashed by huge mesohigh produced by the Sonoran MCS. The outflowsand pressure rises caused surge up through Yuma but everywhere else is being affected by subsidence.The diverging outflow under the MCS may have pushed the subtropical air back southward over the higher terrain of Sonora while squeezing it northward up the GoC channel. Unfortunately, the surge ait has not turned westward yet, as indicated by falling dewpoints at Sells and Sasabe.

So the can of worms is readjusting all over the place and it appears that any storms over SE Arizona will be late or tomorrow. But nice storms have been triggered in Rim country and west New Mexico (see graphic above).

"Nothing is Easy" Jethro Tull

WHAT A DIFFERENCE A DAY MAKES

I overlooked the importance of the upper-level trough off the end of Baja and Pat Holbrook pointed this out to me an e-mail at 8:45 am yesterday, as per:
---------------------------------
Bob, A couple of notes…the upper low off the southern tip of Baja (north of the developing tropical system) should make it favorable again today for strong convection in the sierra madre’s like we saw yesterday…some pushing close to our border...but more importantly moving out away from the mountains into the Hermosillo area. The low turns the corner around the ridge tomorrow which should help out AZ on Wednesday. Satellite precipitable water shows the surge moisture lurking just south of the border and with tonight’s convection we should have a much deeper push into AZ…pressure difference between MHO and Yuma is around 4mb now and should increase some tonight. Pat
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A spectacular MCS developed over Sonora during the evening (see photo above) as the upper trough moved northward. This MCS has pushed outflows and deeper moisture over most of the southern part of state, while in far west Yuma Td has gradually increased through the night. So, what a difference in things today!

At sunrise sky was heavily overcast with thick cirrus from the decaying MCS and a brisk southeast breeze was blowing. Temperature here at house was 81 at 6 am. There continue to be some light midlevel showers spreading north across this part of the state. Other features of note this morning:

Depression Five-E looks more like a TS or hurricane in the morning satellite images.

Upper-level trough is now about half way up Baja.

Precipitable water amounts have increased about ¼ of an inch since yesterday afternoon, and are around an inch and a half over southern Arizona. Most stations in southeast Arizona had outflows during the night form the south gusting 40 to 50 mph.

It appears there may be a circulation and vorticity center left behind by the MCS – it appears to be south of Nogales and moving to the north-northwest. This feature could play an important role in this afternoon’s events. It has certainly destroyed the accuracy of the NAM initialization this morning, which is extremely bad over the Southwest!

Observed 850 mb Tds are still only around 10C at Tucson, Yuma, and Phoenix this morning. But south winds of 15 to 20 kts at all three sites should help further increase low-level moisture during the day. Surface dewpoints are currently mostly in mid-to-upper 50s, except for Yuma which has increased to 70F.

Mexican soundings have reappeared this morning, but probably not in time to get into the NAM initialization.

The Tucson sounding’s winds are very chaotic this morning. The 500 mb wind is from the north because the MCS circulation has popped off a small anticyclone to our southwest – this should dissipate as the MCV moves by and winds at 500 mb will probably return to be southerly, but light, this afternoon.

Not clear how much sunshine we’ll get to fight the low-level cooling from the MCS outflows. Thus, not obvious yet how much CAPE there may be at low elevations this afternoon and evening. But, storms will pose a threat both for heavy rain and wet microbursts.

Should be an interesting day, but with all the features at play it’s a real can of worms. I did note that the Tucson NWS early morning forecast just defaulted to climo of 30% for all 14 forecast periods through next Tuesday. No further comment.

Apparently More of the same

Yesterday’s surge at Yuma mixed out during afternoon and precipitable water remains around an inch and a quarter across southern Arizona, with higher values remaining to the south over Mexico. More early morning convection across the southern Gulf of California (see 1400 UTC visible image above) may help sustain pushes of shallow but more moist air northward.

The 500 mb anticyclone split into two lobes yesterday with the western lobe moving over New Mexico. This morning it looks like the western center is over, or even a bit south of, El Paso. (Soundings are missing for Mexico so far this morning on the SMN site also.) This has shifted the 500 mb winds to southwesterly over Arizona. The NAM consolidates the 500 high as a single center between Tucson and El Paso and then shifts it northwestward from 48 to 72 hours. No features are apparent in the model forecasts that would serve to shift the subtropical air mass back over the Southwestern US – so we’ll just have to watch it day by day.

Yesterday, storms to the south pushed strong, dusty outflows across the Tucson metro area around 5 pm. Rain was reported at 7 of the 93 ALERT stations, mostly to the south toward Green Valley. I do see reports of 0.47” at Tinaja ranch and 0.63” at Picture Rocks so there were some isolated spots of respite from the brain-searing heat. This morning’s Tucson sounding has no CAPE when I modify for the afternoon, and so we’re looking at isolated storms over higher elevations and more strong and dusty outflows.

Ramblings on Monday Morning July 13, 2009

Virga showers came off the Rincons last evening around 6 pm or so with some winds and blowing dust along the Rillito. Mostly hot with high of 107F – 4 ALERT stations (in the Catalina and the Rincon mountains) reported a bit of rain yesterday.

Things I note this morning –

Moisture has gradually increased across south-central and southwest Arizona during past 24 hours (see GOES PW at 1300 UTC above). Yuma had a nice surge between 8 and 9 pm last evening, triggered by yesterday’s MCS, and there is a lot of cloudiness in the GoC this morning and another large MCS south of the GoC mouth.

This morning’s Tucson sounding shows increased PW but only a slight touch of CAPE, so more low-level moisture is needed, but the trend is good. Wind profile quite unusual with L/V winds entire upper-half of troposphere. Looks like lower-level winds will be from northwest this afternoon – hotter out that way but perhaps more moist also because of the surge. So, it looks like CAPE in the mountains and some meandering storms this afternoon. Strong downdraft environment so good chance for outflows off mountains. I'll watch the PW and Tds to see how much impact the surge has.

Upper-levels appear quite diffluent next couple of days, so if moist influx continues, tomorrow could be a more interesting day. The 500 mb anticyclone has remained locked over northwest Texas, and there is very warm air over southern New Mexico. Mid-level temps have remained relatively cool over Arizona. What’s lurking over northern Mexico?

As the S/W that’s onshore in the Pacific northwest moves over the ridge and digs south of Great Lakes at mid-week it will force a westward adjustment of the anticyclone. So, we might have increased activity as the large-scale goes through a period of transition.

Interesting Drive on Friday (July 10, 2009)

Apparently the NAM forecast on Friday morning was reasonably good, and the predicted S/W I discussed that morning led to increased storms with a decent shear profile and some westerly component to the steering flow.

As we drove east from Tucson in the late afternoon there were fairly numerous Cbs in sight from east to south. As we neared the Highway 83 exit there was a solid line of storms to the east that were producing frequent cloud-to-ground lightning strikes. This line was west of Benson and the Whetstone mountains and apparently heading toward Tucson. We drove through a couple of brief, but heavy showers on 83. After several miles, a storm was about to come over the Empire mountains, and I took the photo above at 6:30 pm MST. Yes, that’s the Tucson WSR-88D on the far right side. Winds were from the east at 30 to 40 mph when I took the photo.

Storms were weaker on to the south, but lightning continued, along with rumbles of thunder, until after dark (location 5 miles northwest of Sonoita). A perfect evening outing for a weatherman.

The storms rapidly moved into the Tucson area with damaging winds and frequent lightning (as per the shot from the Computer Sciences web cam). There was 0.34” in the gauge when we returned yesterday evening. There was measurable rain on Friday at 43 of the 93 Pima County ALERT gauges and these were mostly in the eastern half of the network.

Intense MCS Along GoC Coast

An intense MCS with multiple extremely cold cloud-top centers has been moving rapidly along the east coast of the Gulf of California toward the north-northwest. The convective event began yesterday evening, and this system has been propagating up the coast from south of Mazatlan and has now reached the central GoC. Two obvious and important questions - how long will it continue to maintain its intensity? and will it/has it intiated a strong northward surge of low-level, moist sub-tropical air? More later today.

From Ron Holle re Storms 10 July 09

Bob-

We were at dinner next to campus Friday night about 7pm. The Webcam caught the attached view as the rain shaft and frequent lightning moved across town from SE to NW.

Ron

Storm Activity Down Yesterday

Yesterday was a day of reduced thunderstorm activity in far southeast Arizona; however, storms again developed near the Santa Rita mountains and moved northward, with some dissipating over the Tucson metro area before sunset. The partial rainbow photo (on the blog) was taken looking east-northeast from the backyard a bit before 8 pm last evening.

Only 5 of the 93 ALERT gauges reported rain in past 24 hours and amounts were light. I did note that the Empire RAWS station was hit by a heavy storm for the second day in a row and it reported 1.00” in a brief period yesterday afternoon.

Today is yet another problematic forecast situation. The Tucson morning sounding indicates a small amount of CAPE for late day, high-based storms. The lapse rate is nearly adiabatic to 500 mb, so that any increase in low-level moisture from the south/southeast would quickly increase CAPE.

The 500 mb anticyclone is positioned aloft near Wichita Falls, Texas, and winds are southerly at all levels above 600 mb here over Tucson. It appears that the hottest and driest air circulating around the anticyclone will stay a bit to the east of here today. Of course, as everyone has been mentioning, the lack of any upper-air data from northern Mexico for the past 8 days makes for much uncertainty. This is complicated by the NAM forecast which indicates a distinct S/W at 500 and 700 mb moving across southeastern Arizona this evening. In the model, this feature yields a good shear profile as 500 and 700 mb winds become east-southeasterly. Thus, an increase in coverage and intensity of storms is possible this evening – assuming the model has a fair degree of accuracy over northern Mexico.

We are heading to the grasslands near Sonoita this afternoon and tomorrow, and I’ll report back on Sunday on the storm activity we observe down there in the hinterlands.

Fool Me Once, Fool Me Twice.......

Yesterday I said that I’d be surprised if any ALERT stations in the Pima County network caught rain. Well, I was certainly surprised and quite amazed that an apparently (to me – Pat Holbrook had warned on Tuesday that Wednesday might be a big day) hostile environment produced a round of severe storms and heavy rains.

I shot a photo of storms approaching the house (taken about 5:45 pm on the 8th) from the south – see above – and we had 0.39” here at house. Airport got double that; 60 of 93 ALERT gauges caught rain; The Mt. Hopkins RAWS site recorded 2.60” and the Alert gauge on far south Wilmot had 2.13”; a number of warnings and alerts were issued by NWS; and severe storms were reported near Green Valley (wind) and San Manuel (wind and ¾” hail). So, it was not exactly a quiet day.

While the precipitable water was trending down in the morning, it stabilized and held through the afternoon, while Phoenix actually increased some. So, the northwest winds coming off the low desert were not bringing in drier air, as I’d expected. The big storms that developed on and around the Rincons generated strong outflows that moved to the north (downhill). The resulting convergence zone over the metro area produced the storms that moved across much of the city.

Doing a quick postmortem, I see that I had not accounted for the rapid shift eastward of the 500 mb anticyclone - from near Yuma on Tuesday evening; to northeast of Tucson yesterday morning; to south central New Mexico yesterday evening; to northwest corner Texas Panhandle this morning. So, it was a rapidly changing large-scale environment, which favors storms as opposed to a stagnant anticyclone. Pat H. or Erik P. had mentioned this fact, but it eluded me yesterday. The shifting high acted to shunt terribly hot 500 mb air northward and the shifting flow overhead appeared to bring in some slightly cooler 500 mb air from the vast data voids of northern Mexico.

So, conditions here in southeast Arizona fought off the deep dry air that impacted much of the west and north parts of state yesterday. This morning the PW is definitely trending down, surface flow from the south to southeast appears to be bringing in drier air. The NAM keeps some convection in southeast Arizona today and then shuts it down tomorrow, as very dry air in the upper-troposphere swings around the bottom of the upper anticyclone. Me, I’ll just watch today and see if my Tuesday outlook verifies two or three days late.

Bob

Beat Up by the WRF

Yesterday was a tough day for an old-time forecaster, as the WRF forecast totally out did my assessment that the hot and hostile air in upper half of troposphere would dominate the low-level moist surge. If anything, there was more storm activity here in the southeast corner of the state than the model predicted. One small tower went up right overhead and gave us 0.02” in a minute or two and then it was gone. A storm out west of the Tucson Mountains produced a gust to 59 mph at Ryan Field. Nogales got hit with a serious storm that gave them a gust to 48 mph and over an inch of rain in a short period. The NWS forecasts were quite good yesterday, especially the early am update based on the new sounding data.

As for rain here in the extended metro area, the ALERT network shows spotty reports with the most concentrated measurable rain occurring in the south and southwest portion of the network. Nine of ninety three gauges had measurable precipitation before 6 pm and another 12 measured rain after 6 pm (21 of 93 with precip during past 24 hours).

This morning conditions were deathly clear at sunrise, quite a contrast to yesterday. Even though there is still CAPE in the morning soundings, the middle to upper troposphere is even more hostile today. The surge ended late yesterday afternoon and GPS precipitable water is trending down across southern Arizona. The anticyclone at 500 mb has shifted eastward and is now centered a bit northeast of Tucson near the Arizona/New Mexico border. Temps at 500 mb are an ugly -3 to -4C.

So, I’ll just recycle my discussion from yesterday and say that I expect storms today only over the higher terrain of the borderlands and far east. I’ll be very surprised if any of the gauges in the Pima County ALERT network catch any rain today.

Amazing Changes Overnight

Miscellaneous Ramblings

Sky at sunrise looked quite chaotic, much like it does on big storm days. Was a muggy 80F at 6am here at house. ACC all directions except northwest and even some low cloud based below the tops of the Catalinas and the Rincons. Amazing changes as the dry Pacific air aloft battles the influx of low-level moisture from the Gulf of California and from outflows from borderland storms.

Significant Gulf of California surge began yesterday morning between 7 and 8 am and has continued ever since. It’s remained fairly deep extending up to 4 to 5 thousand feet as per the radar VADs. Tucson’s morning sounding is quite impressive below 525 mb and indicates precipitable water of 42.57 mm – as said above a remarkable change overnight. The GPS data indicate that the sounding is a bit too wet – about 3 to 5 mm.

The WRF sounding Mike Leuthold sent out yesterday was very moist – BL mixing ratio of 12 g/kg and lifted parcel theta-w of 24C – both values are higher than has been observed yet this summer. The WRF certainly picked up on the changes, but still predicted only isolated convection mostly south and east.

Temperatures above 525 mb are very warm and will be increasing a bit during the day. Phoenix sounding much drier than down here and that superheated air will again be trying to advect this way. The 500 mb anticyclone begins its eastward position shifting during the day and much of southern Arizona should be under the influence of subsidence in the upper troposphere.

So the question is how this battle will play out during the day – will the nearby mountains trigger significant storms before the hot air aloft chokes everything down? Will the low desert BL air with no CAPE invade the local area? Tough questions – my guess would be that things get too hostile in the Tucson metro region and that storms will again be mostly east and south. I still would bet Mike Leuthold a beer that the WRF predicted afternoon sounding for Tucson will prove too moist and unstable when the afternoon sounding data come in. But would I bet a crisp Ben Franklin – no way!

Mike Hardiman Wrote to Art Douglas

There's obs down there... just need to dig pretty hard to find 'em:Sonoyta, Caborca, Nogales, San Luis:

http://smn.cna.gob.mx/productos/emas/

Puerto Penasco:

http://www.cedointercultural.org/Current_Monitor_original.htm

Several Others:

http://clima.inifap.gob.mx/redclima/clima/default.aspx?estado=25

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.