More on Phoenix Rains

Finally, a worthy report from up North. A "peaceful, easy feeling" now resides over the city of Phoenix with continued drizzle from a rather active night. Around 10 pm, outflow boundaries from southern storms produced areas of blowing dust at Sky Harbor reducing visibility to 1 mile. Wind gusts were reported at 23 kts. Converging outflow boundaries from notheastern and southern storms generated thunderstorms over the metro area producing spectacular lightning and much needed rainfall. Most of the rain gages at the Flood Control District of Maricopa County measured precipitation. The heaviest hit areas were along the I-10 corridor and south of the city. Gila Bend recorded 0.79 inches of rain with 0.48 inches falling between 0252 and 0322. Nearby Waterman's Wash recorded 0.75 inches with 0.39 inches falling between 0407 and 0422. Near Jefferson Street and 4th Ave, flooding was reported due to 0.83 inches of rainfall. The highest observed rainfall amount was recorded near the base of South Mountain with 0.94 inches of which 0.72 inches fell between 0253 and 0323. For more detailed rainfall information, please visit Steve Water's FCD site at


http://www.fcd.maricopa.gov/Rainfall/Raininfo/raininfo.aspx


Also to note, preliminary reports of a microburst occurred at Luke Air Base with wind gusts of 69 kts recorded at 22:22 to 22:26 in the Mesowest network.

Melissa Wagner, ASU

A Showery Morning

What a pleasant change – cool, light showers, and heavy clouds (see 7:20 am KEMX radar chart). The subtropical system from Mexico did arrive a bit more quickly than the models indicated and easterly winds in mid-levels increased substantially during the afternoon. Thunderstorms developed on the mountains and moved into Tucson around 5:30 pm with gusts to near 50 mph and blowing dust. CAPE was apparently limited and neither TUS nor DMA carried a thunderstorm. A cell over the west flanks of the Catalinas developed after the first push and produced two rumbles of thunder here at house. I saw one CG strike to the north in the foothills. I should have paid more attention to my admonition on Tuesday that events such as this often develop more quickly than the models indicate.

Almost all observing stations in a large area of southeast and south-central Arizona had measurable rainfall, although amounts were generally light. In the ALERT network in Pima County only 8 stations did not measure rain. Five of the stations had 0.50” or more and Arivaca measured 0.94” – most amounts were around a quarter of an inch. The same is generally true for the Phoenix metro area ALERT network also (with the storms and rains arriving during the night and early morning hours this is the first significant rain event of the summer up there) with almost all stations having rainfall except for a few on the eastern edge. The rain amounts appear to have been heavier in the Phoenix network. Luke AFB had thunderstorms, gusts to 69 mph, and also the most rain reported at 1.00”.

There is substantial CAPE present in the TWC sounding this morning but obviously heating will be limited. A strong outflow from the mountains would likely produce spectacular storms with winds and R+ given the sounding – we’ll have to watch to see how the details evolve. There does appear to be instability for parcels lifted from elevated layers, so the forcing with the subtropical low, coupled with that of the mountains, should keep showers going off and on through evening. The low is being picked up by an upper S/W coming across the Southwest before the larger trough to the northwest affects us, drying things out again for several days. Abbreviated message – I have to get into Atmo for the daily discussion.

Yesterday - Definitely Not An Uptick Day

The cloud cover certainly won out yesterday. Slightly cooler temps, higher pressures and a retreat of the moisture back into Mexico dominated our weather. Radar precipitation estimates show that all of southeast Arizona was quite suppressed yesterday. There was no rainfall recorded in the ALERT network. The only uptick was a brief increase in moisture and the stubborn cloudiness. I’ve posted several data plots on the blog that illustrate the dismal precipitation that’s occurred during the summer so far across the state.

As for today – MCSs have formed and dissipated through several cycles in Mexico during the night, while propagating northward (see 1330Z IR image). The satellite imagery this morning shows a large cloud mass covering most of western Mexico that is moving northward.

The soundings this morning at Phoenix and Tucson have slight to no CAPE and thus the issue of whether cloud cover hangs around or not today is probably not of great importance. The nocturnal activity in Mexico appears associated with a distinct inverted trough at 500 and 700 mb. The NAM model continues to forecast an important precipitation event across much of Arizona as it forecasts this feature to move northward, split the anticyclone apart, merge with a weak upper S/W in the westerlies and then move eastward. Thus, the model forecasts an interesting interaction of features from the subtropics and westerlies, all accompanied by a large push of moisture and precipitation northward into the U.S.

It appears that this transition has begun and that it will affect southern Arizona beginning late afternoon or tonight and then continue into Friday, bringing the subtropical air mass finally back into Arizona.

Recent Precipitation and Dewpoint Data For Phoenix

Phoenix rainfall and dewpoint info of interest...

http://www.wrh.noaa.gov/psr/pns/2009/August/Brief1.php

Was also /very/ dry in Phoenix this weekend...

http://www.wrh.noaa.gov/total_forecast/getprod.php?prod=XXXPNSPSR&wfo=psr&version=0

-Paul

Finally - How Have The Last Two Weeks Gone?

This figure for the last two weeks illustrates graphically why I have been referring to the "failed monsoon." This figure is from the Western Regional Climate Center (WRCC) at the University of Nevada. http://www.wrcc.dri.edu/anom/ari_anom.html

It appears that the only way we can go is up!

July Precipitation for Arizona

This figure is from the State Climatologist's (Nancy Selover) July summary for Arizona shows the month's precipitation as a percent of average. It shows that several areas in the state were wetter than normal, but that July has been dry for most of the state. The complete July summary can be found at http://azclimate.asu.edu/

More on Salt and Verde Summer rains

This slide shows how the entire summer rainfall total (June 1st through September 30) for the watersheds ended up relative to the rainfall in early summer (this chart also from Jon Skindlov). Note that only one year (2008) of the past ten that was normal or dry during early summer recovered in August and September to end up as a wet summer.

Summer Precipitation So Far - Verde and Salt Basins

I thought that I'd add a bit of information to the blog posts illustrating how the summer has gone so far around the state. The above slide (thanks to Jon Skindlov) shows watershed averaged precipitation of the combined Verde and Salt watersheds. The period covered runs from June 1, 2009 through August 9, 2009. It has been a dry July in these watersheds with rainfall accumulation through the 9th standing at 62% of average.

Heavy Clouds At Sunrise

Yesterday storms occurred to south and southeast and also briefly on the Catalina and Rincon Mountains. A large MCS developed (see 03Z IR image above) with most of the active cells staying south along the borderlands (Nogales had thunder, rain, and gusts to 46 mph), but outflows spread north through most of southeast Arizona bumping the dewpoints back up. Heavy clouds covered the sky this morning – remnants from last night’s MCS. Measurable rain occurred in the past 24-hours at 6 of the 93 Pima County ALERT gauges, with Manning Camp high in the Rincons measuring 0.67”.

The most interesting changes overnight occurred across south-central and southwestern Arizona where a surge of low-level moisture from the Gulf of California occurred, bringing some dramatic 24-hour increases at 6 am. As per:

Needles CA +33F; Yuma AZ +24F; Phoenix AZ +21F; Casa Grande +18F

So two issues for today will be: 1) how quickly will the cloud cover break up to allow heating? 2) will low-level moisture continue to slowly increase? Note that with precipitable water up to around 40mm in the PHX and TWC soundings we have had a nice increase, but the really moist subtropical air has not quite moved into Arizona. The soundings indicate that we will probably still have quite limited CAPE at low elevations this afternoon. South winds at Guaymas extend up to 700 mb, so there are good signs that things will continue to improve today and tomorrow.

The western circulation center of the massive, mid-level anticyclone that covers the southern half of US and much of the subtropics has consolidated along the New Mexico/Arizona border. This provides a nice wind profile for moving mountain storms toward the deserts. The NAM forecasts that the subtropical moisture will push north and interact with a weak N-S trough embedded within the anticyclone – the result is that the model forecasts the most active days to occur on Thursday and Friday. Since the model is often slow, tomorrow might be the day that we see much increased activity, after another uptick today.

An Uptick

Low-level moisture has slowly increased over southeast Arizona (see plot of GPS PW trend at TWC) since mid-day yesterday, essentially south of line from Douglas to Oro Valley to Sells and out through Why. Morning dewpoints today are 10 to 20F higher than yesterday morning and surface pressures are up 2 to 3 mb – so some good and some bad in the obs. There has been weak southerly to easterly flow aided by outflows from storms along and south of the border. There does appear to be a weak surge signal in low-levels of the Guaymas sounding this morning. But overall it’s a pretty chopped up synoptic pattern, with mostly westerly flow over the southwest U.S. at 500 mb. Definitely more CAPE along the borderlands today. If Tucson were to mix out to 8 or 9 g/kg this evening there would be a silver of CAPE here at lower elevations.

The NAM indicates that today will be a day of adjustment at 500 mb with the small anticyclone center that’s over northwest Sonora this morning trying to consolidate over New Mexico. The main center remains over the far southeast U.S. A weak inverted trough extends from southern end of Gulf of California to the bootheel of New Mexico. The NAM continues to strengthen this trough some and move it slowly up into southeast Arizona. If this indeed occurs, it will help push moisture and outflows northward and that could lead to considerably more storm activity this evening and especially tomorrow. The NAM appears to have a convective feedback effect going between noon and midnight in the area between Nogales and Green Valley, where the model forecasts a rain bulls-eye of around 3 inches. So, we should keep careful watch to the south today to observe whether the model has latched onto something other than an internal convective runaway.

The NAM forecasts a substantial increase in moisture and precipitation on Wednesday and Thursday, as it apparently shifts the subtropical air northward for a couple of days. So, it looks like a week of much increased possibilities for rainfall than what we’ve experienced in past several days. In the longer term, the ECMWF is again very aggressive with the next Pacific trough and brings it inland across all of the west, putting the Fall-like pattern back into play.

Beautiful Fall-Like Morning in Tucson (9 August 2009)

It was a crisp and very sparkling morning here at the house. I didn’t check the thermometer until 6:30 am and it was then at 64F – may have been lower. I see some stations away from the city were in the 50s. Unfortunately, we now have had 3 more consecutive days with no rainfall across the Pima County ALERT network.

Not much more to say about current conditions. Precipitable water amounts are less than half an inch across the state except for the far southeast where amounts are hanging in there at three quarters of an inch.

The morning upper-air charts show a large, inverted trough in the easterlies (present from 200 mb down to 700 mb that arcs from Arkansas to the region near and south of the southern end of the Gulf of California). This feature is butting heads with the unusually deep trough in the westerlies that is affecting all of the US west of 100W. Looks like the inverted trough in easterlies will shear apart – with a portion in lower troposphere moving out into the Pacific (see below re model TS development) and the portion from Texas to Arkansas pulling away to the northeast – leaving a weak trough over Mexico. There is 700 mb cool advection into the lower Gulf of California which will keep pressures relatively high down there, perhaps pushing more moist low-level air toward southern Arizona.

The NAM forecasts this morning indicate several interesting developments by Tuesday and Wednesday. The model spins-up a new Tropical Storm southwest of Baja. It also appears to consolidate the remnant inverted trough over central Mexico and swings that strengthened feature northwestward across western Mexico and into Arizona by Wednesday afternoon. While this is happening, the model shifts the western center of the subtropical anticyclone northward toward the Four Corners region. If the events depicted in the model forecast actually transpire, we would see a significant low-level surge of GoC moisture into southern Arizona as early as Tuesday morning leading to a return of thunderstorm activity.

So, there are some things that we should keep an eye on as the new week gets underway.

Bad RRS Data Affect Short-term Forecasting

Shown above are the GPS precipitable water estimates for the TWC (Tucson) sounding site for the past five days. Note that there is a slight dry bias for the morning soundings during this period, but the afternoon RRS sonde data dry bias is very large. My contention is that these are unacceptably inaccurate data for use in short-term forecasting (often the most critical public forecasts that the NWS makes).

On the evenings of August 4, and again on the 5th (00Z on the 5th and 6th), strong storms were approaching the Tucson metro area from higher terrain. The observed and transmitted soundings for TWC have absolutely no CAPE available for storms. This is because of the extreme dryness indicated by the RRS sondes in the deep boundary layers. The sounding on the 6th appears to have "missed" 5/10s to 6/10s of an inch of the actual precipitable water present.

My second contention is that there is no way that a forecaster can quickly guess what the actual sounding structure might be - this is of course a game with infinite solutions. Strong storms, gusty winds and restricted visibilities due to blowing dust occurred on both evenings. Who knows how some future researcher might interpret the archived, official, RRS upper-air data with the observed weather?

The bad data, of all types, in the RRS soundings constitute a serious problem that no one in NWS management seems to want to talk about, much less formally warn the external user community.

Personal note - I'll be out of town witout computer access tomorrow.

Here We Are Again

Very suppressed yesterday except for far east. Hot dry winds yesterday and again for today. The bit of rain that fell Tuesday and Wednesday is now blowing in the wind toward Kansas.

Satellite image for 1500Z shows skies mostly clear across all of Arizona. Dewpoints are mostly upper 20s and 30s with some 40s in far southeast.The western trough and 90 to 100+ kt upper-jet across Arizona makes the pattern appear as if Fall is here. So, the question for now is how long the dry weather will continue. Or I could say that the failed monsoon had a two day break with some storm activity in the southeast, but that it (the failed monsoon) came back quickly.

There are two very large inverted troughs off to the east- one stretches across the Gulf of Mexico and the other is out in the west Atlantic. The GoM feature extends down to 700 mb and will push west and do battle with the western trough in the westerlies. Forecasts indicate this feature will shear apart with the lower portion weakening and coming across central Mexico.

Looks like that's about the main thing we have to watch the next several days. Summer 2009 - so it goes.

Outlook For Today and Beyond

The small S/W at 500 mb that was the focus of yesterday’s activity moved north further east than the NAM predicted and is over southwestern New Mexico this morning. The northward movement of this feature – combined with the onshore movement of the California cutoff – has realigned features at 500 mb. This morning there is one anticyclone center over the southern GoC and one over the eastern Colorado/New Mexico border. Arizona is now within the southwesterly flow regime around the cutoff low.

Dry low-level air is present over western Arizona; however clouds and light showers linger from Nogales into the Phoenix area. The upper-air charts and VAD winds indicate that drier air should spread eastward today and limit storm activity to the higher elevations of the state, basically east of Tucson to Flagstaff line. Both the Tucson and Phoenix soundings were modified by the cloud deck overhead. The Tucson sounding also had several superadiabatic layers that produced a false cooling in the layer from 520 mb to 450 mb.

The NAM forecast indicates that storm activity shuts down through the weekend, with anticyclone in southwest again pushed into northern Mexico, and the main lobe of 500 mb high pushed far to the east. A very large inverted trough (one of the few we’ve seen north of 20N this summer) is forecast to be moving westward across central Mexico over the weekend (see above 84-h NAM forecast), while the tail of the west coast trough is sheared off and left behind off the coast of southern California and northern Mexico. So, it appears that the larger-scale situation will again become very complicated as we start next week.

Finally, Tropical Storm Felicia was named by the NHC two days ago and was forecast to remain a TS – but this morning she is a Category 4 hurricane. Too far away to be of interest to us, but folks in Hawaii are probably keeping a close eye on her.

Summary of Yesterday

Image shows storm and downburst on west flanks of Catalina Mountains at 6:30 pm MST yesterday afternoon. There were quite a few storms over the metro Tucson area and this one back-built to south merging with other cells. Three distinct rain periods at house produced 0.50" of rain - the most rain in a day at house since the 4th of July.

There was measured rainfall at 43 of the 93 gauges in the ALERT network. There were six gauges that recorded 0.50" or more and the max amount was 0.91" - not bad for such a hot and dry boundary layer. The airport observing station recorded dust, a gust to 44 mph but only a Trace of rain. Nogales had winds to 35 mph; Davis Monthan AFB had gusts to 33 mph; and the rooftop anemometer at Atmo hit 60 mph.

Here in the north part of town the lightning was was quite wicked during the onset of the storms.

Unfortunately, the Nonsoon continues up in Phoenix region.

Outlook For Today

There apparently wasn’t enough rain from yesterday’s high-based storms to support much recycling, and the morning soundings remain quite dry below 600 mb. There will likely be CAPE available at low elevations this evening, but the TWC soundings have been so bad this week that there’s little help available from them. Last night’s sounding provided no help at all for making a short-term forecast as thunderstorms approached from the east (see radar image on blog). The sounding was apparently about a HALF AN INCH too dry wrt PW! One could make guesses with an interactive routine to try to “fix” the sounding but those are still guesses. One of the stronger storms propagated toward the south and hit the radar site in the Empire Mountains, knocking the radar offline for much of the evening.

I note that the Phoenix sounding this morning has increased PW at 42.1 mm, which is a good sign for this afternoon. There have been problems with the GPS PW network, so there is little info available for cross-evaluation.

Another dilemma this morning relates to the NAM analyses and then its forecasts for this evening. The 500 mb anticyclone is quite strong now and centered over northern New Mexico. The NAM analyses indicats a weak S/W southwest of El Paso – satellite loops indicate a feature in this area moving toward the west-northwest. (The 700 mb plot indicates that a weak inverted trough extends north from the southern end of the GoC into western New Mexico, further indicating that there’s a feature where the model thinks it is.) The NAM forecasts this feature to intensify during the day and move into southeastern Arizona this evening. The NAM forecasts an excellent setting for severe storms this evening and it would likely be a very significant storm day if there were a more moist and unstable boundary layer present. As it is though, there will likely be a bit more CAPE today and there should be an increase in storms with more winds and dust and nice lightning displays.

My outlook for here at the house is that today is the best day since July 22^nd and that measurable rain chances are about 50%.

Big Dry-Out in Tucson Area is Over

Photo taken last evening (Tuesday 4 August 2009) from house looking southeast at a shower that is over the eastern part of town around Kolb and Golf Links. Most storms stayed over higher elevations and the most intense storms split around the core of the Tucson downtown. After dark there were nice lightning displays north of the Catalinas and also to south and northwest. Rain was measured, although amounts were light, at 34 of the 93 Pima County ALERT gauges. So, the long, totally dry spell has ended.

Although, as post below notes, other parts of south-central Arizona have yet to have significant rains at all this summer. Here at the house we had rumbling thunder several times during the late evening and a nice sweet smell of rain - but not a drop nor a trace of precipitaion. So the local dry spell here at house continues with no rain since the 0.44" that occurred on the 22nd of July.

So Far This Summer It's a "Nonsoon" in Phoenix Area

With the monsoon taking another lengthy break (it has basically been non-existent all year for us folks in Phoenix) I noticed that our average dewpoint since July 4 in Phoenix has been a pitiful 51.03F. Just this last week dew point temps have averaged: 48, 49, 48, 42, 37, 40, and 43F. Really is too bad considering we are headed into another long stay of very dry weather. It would certainly be nice to see some semblance of the monsoon...especially up here!

Chris Wrobel

A Quick Post - Have to be Other Places

Brief Overview of Conditions This Morning (Tuesday 4 Aug 2009)

The strong complexes of storms along the border (02Z IR image) last evening pushed outflows into southeastern Arizona and also squeezed on the GoC air mass sending a push of more moist air northward into southwestern Arizona. The net result is that surface dewpoints (roughly west and south of line Douglas to Safford to Kingman are up 7 to 11F relative to this time yesterday. The soundings this morning at Tucson and Phoenix show that the increased moisture extends to about 850 mb and a VAD out at Yuma shows south-southeast winds of 15 to 20 kts extending to about 3000 ft MSL. So, finally at least a modest increase in moisture (note that Atmo’s GPS PW time series are down and have been since last evening).

Manning Camp at 8200 ft MSL in the Rincons measured 0.04” in anvil sprinkles last evening. This is only the second time a gauge in the Alert network has measured rainfall for the period that began on Sunday July 26th.

Although the moisture is up, the soundings continue to indicate a difficult situation if storms are to get going at lower elevations. The data at Phoenix and Tucson show a dry-hot residual boundary layer above the new moist layer, that extends to above 600 mb. So this morning’s new cooler and moister surface boundary layer will need to continue to moisten and deepen and not mix with the old boundary layer aloft. However, winds are northwesterly to northerly and fairly strong in the elevated layer. If a surface boundary layer with moderate CAPE can maintain itself today (which I doubt), then a good outflow kick from higher-elevation storms could shift the activity into the deserts. My estimate is that the afternoon boundary layer will be well-mixed at 7 or 8 g/kg which gives a small amount of CAPE that would have to contend with the warm inversion that exists around 450 mb. So, a very complicated, but more interesting, situation today.

Morning NAM not available. I note that winds seem to have broken through already here at house since I wrote above and are from the northwest.

500 mb Chart 00Z 4 Aug 2009

The above chart is 500 mb for 00Z 4 August 2009. The chart shows that the center of the anticyclone is well-established over the White Mountains of Arizona. It is an excellent pattern to allow thunderstorms to propagate westward into the Tucson metro area, assuming that low-level moisture and CAPE have also been brought into place over the lower elevations. This pattern is not favorable and will not bring these necessary ingredients into the Tucson area, unless other features are in play in concert or before. Thus, we have thick anvil cloud but no covection this evening in Tucson because at sounding time the low-level atmosphere was hot and dry and ugly and there was not even a sliver of CAPE. The lack of subtropical, low-level moisture locally probably relates to the fact that the 500 mb anticyclone is HUGE with its southern periphery reaching to Yucatan.

Anvil Cloud from Mexico

Photo from backyard of heavy anvil coming out of thunderstorm cores in Mexico on the strong winds around the 200 mb anticyclone. Photo also captures some very high based cumulus clouds. Temperature and dewpoint at TUS at time of photo were 103/41F. Another dry and ugly hot day.

Reasons For the Monsoon Fizzle

In communicating with the SMN best we can tell it was the 700mb height pattern across N.A. and the Atlantic that was the problem: a block in Canada, a trough to the south in the eastern US and deep trough off Europe. The US trough directed dry northerly flow into Mexico for most of the month with easterly waves being sheared by the two troughs to the north as they tried to make it westward. El Nino probably contributed to the pattern as Great Lakes troughs are more common in August with El Ninos) and the QBO changing to a strong East Phase is also associated with lower rainfall in Mexico (and India).The cross equatorial flow index (SLP gradient Easter Island to Costa Rica) stayed high all month suggesting good flow from the south into the ITCZ. Problem is there were no wild swings in the SLP gradients to promote wind bursts to push the ITCZ north into Mexico. June had some strong pulses heavy rains and good TC genesis east of 110W, but not July which saw storms form well offshore and west of 110W. The very high index (>10mb)is counter to any farther development of El Nino at this time. The Aussies have noted the same in their daily discussions pointing out that the SOI is very high and counter to strengthening of the event.

Art Douglas

Broader View on the Monsoon

Here is a bar graph of the all-Mexican rainfall. The blue bar is the observed rainfall, the yellow the climo and the red bar the forecast. It looks like it will turn out to be the driest or second driest July on record .... the SMN still needs to add the 8AM August 1st totals to the graph for the month (Mexico rainfall in the morning of the 1st on the previous month's total).

The Mexican monsoon did have a good start........and fizzled earlier than expected under the El Nino which strengthened in May and June. The August forecast calls for 92% normal for Mexico but 70% of normal in the area from Durango to Tamaulipas and the southwest coast from Colima to Oaxaca. This will be a classic dry El Nino summer for Mexico if August remains dry as forecast.

Art Douglas

Comments Regarding Yesterday

Except for a cluster near Safford bit of a dud yesterday. What moisture increase there was in the BL was washed-out through-out the day, as evident by wide-spread surface dew points in the 30s and 40s. Still looks like June to me.Models (especially the aggressive NAM) are trying to bring some moisture in here the next few days, but they have generally been on the "wet" side this whole season. Yes, there is a weak-looking low near the southern Baja tip that is poised to move northward in the flow, but if I had a nickle for every meso-low floating around that moved into AZ and didn't produce precip I'd have a ton of nickles. With the stronger w/sw flow one would think this feature might get sheared-out anyways.Large-scale flow pattern looks pretty terrible for the next 1-2 weeks for getting any big activity in the region, especially for the Phoenix area. If it stays this dry into mid-August, this has the potential to be one of our worst convective seasons on record (heck, already has that potential as of now).

Paul I., Phoenix

More of the Same?

There was some storm activity over southeastern Arizona yesterday afternoon (see radar image for 6:15 MST above). These storms developed mostly at higher elevations in the zone between terribly hot and dry northwesterly flow from the Sonoran Desert and the more moist, recycled low-level air that had seeped into Arizona, east and south of Tucson, from New Mexico. For the eighth consecutive day there was essentially no precipitation measured across all of eastern Pima County (at sunset I could see a light shower to the distant northeast). The moist, low-level subtropical air over Mexico remains over Mexico, as if there were an impermeable fence along the Border!

There was relatively little convective activity over Sonora yesterday evening and last night, so that, without other features in play, there remains little forcing to push this air northward. Values for precipitable water remain at 1 to 1 ¼” this morning across all of southern Arizona.

The morning soundings at Phoenix and Tucson continue to paint a dismal situation with very deep afternoon boundary layers indicated; just a sliver of elevated CAPE; and desiccating northwesterly winds below 700 mb. The wind filed is very chopped up in the lower-troposphere and the winds in upper-troposphere are west to southwesterly around the cutoff low west of California. Storms this afternoon will tend to be over higher terrain to the east and south, as per yesterday, with high bases and gusty outflows. I note that Safford had a gust to 52 mph and dust yesterday afternoon but no rain, Guthrie RAWS had gusts to 46 mph and 0.09”, and Columbine RAWS on Mt. Graham had 0.94” of rain.

The 500 mb chart this morning indicates that there are two circulation centers for the anticyclone: one over the White Mountains of Arizona and one over southern Sonora. There is a weak trough separating these centers. Previous NAM runs (until last evening’s) had forecast this trough to consolidate and swing westward across southeastern Arizona. This morning’s NAM forecast indicates this feature shifting eastward to the Big Bend of Texas and not playing a role in today’s local weather – so not much model consistency in this weak summer pattern. At 200 mb a huge and intense anticyclone continues, centered over north central Mexico.

There is hope for an intrusion of better low-level moisture and some real CAPE for much of southern Arizona at mid-week as the 500 mb cutoff pushes ashore in California. This increases southerly winds briefly, before the cutoff in effect establishes a mean trough over the western U. S.

Is Today the Day?

Another terribly suppressed day yesterday that extended the dry-out to 7 consecutive days. During these seven days 1 site (Anamax) in the Pima County ALERT network reported rainfall (0.16”) on one day (Friday). Can’t help but wonder if this is a record? The “monsoon” has been essentially in a failure mode for Arizona for a week (break seems too mild a term). One could also say that to our northwest in the Phoenix area that it is debatable as to whether there has even been an onset.

Much of yesterday’s discussion is still in play. But there are several things of note: Low-level moisture has pushed in from southern New Mexico during yesterday evening and last night. Between 6 pm and 11 pm surge-like increases in surface dewpoint occurred at Hachita Valley NM, Guthrie, Rucker, and Safford with Safford (yes! Safford) having the highest PW (this side of the border) shown in the time series at Atmo weather page. To the south, moisture remains high and the visible image for 1445z shows middle cloud floating around this morning. There may be a plume of lower cloud moving north between Sells and Yuma. So moisture is encroaching from the east and south, and today will apparently be a day of important change. The morning sounding at Tucson is frankly a disaster with bad data on top of an incredible dryness; whereas, the El Paso sounding looks much more like August (note GPS PW data is not available for El Paso this morning but sounding data indicate almost 3 cm).

The NAM forecast continues to bring the embedded IT at 500 mb (mentioned yesterday) toward southeast Arizona this evening, and then moves it very slowly toward north for next 48 hours, along with a distinct upswing in forecast precipitation coverage. In the longer term, the GFS has now joined the ECMWF in predicting the Pacific trough inland, returning to a very non-August-like and dry pattern later this week.

So It Goes

Things have continued mostly dry except for some storms along the borderlands. Around 4 pm yesterday afternoon a high-based storm popped up west of Green Valley. The TWC 00Z sounding, again way too dry, indicated that there was likely no CAPE at the NWS building on campus. A weak outflow from storms near Nogales may have triggered this surprising little storm, which completely vanished as quickly as it popped up. However, this storm blip illustrates the “tipping point” nature of the stand-off between the wet and dry air masses along the border. There was a large MCS over Mexico last evening (see 03Z image above) that had tremendously cold cloud-top temperatures. The anvil and convective updrafts were undoubtedly venting directly into the stratosphere! Some portions of the MCS dissipated over the southern GoC, but essentially the event remained quite far to the south. Upturns in the surface dewpoints from Douglas west to Yuma this morning may indicate a northward push of outflows from this MCS.

Soundings at Phoenix and Tucson this morning are very dry and stable – as if it were still June. The anticyclone at 500 mb remains very large but unorganized with weak circulation centers and embedded trough lines. Models continue to forecast that it will consolidate toward the Four Corners region. The NAM strengthens the 500 mb flow after 36 hours and brings a nice inverted trough across southeastern Arizona on Monday afternoon – first real hopeful sign in the models for several days! Of course this time of year the reliability of model predictions falls off very rapidly after 18-24 hours, so we’ll have to watch to see how this actually plays out.

This said, I might as well dig a deeper hole and mention some aspects of the longer range forecasts of the global models. The 00Z runs of the operational members of the ECMWF and the GFS have markedly different forecast solutions for the 500 mb pattern at 168 hours. The ECMWF brings the cutoff low that is currently west of California onshore and establishes a trough over the western U.S. In contrast, the GFS moves the cutoff slowly to the north. The ECMWF has a flat ridge across the eastern U.S. with the anticyclone over Arkansas and the persistent great Lakes/East Coast trough pushed away. The GFS keeps the strong trough over the east and thus blocks the anticyclone far to the west along the Arizona/New Mexico border. If the ECMWF proves to be the better long-range forecast, our first week or so in August would go down hill after next Monday. Something else to watch during the coming week.

Mike Leuthold Comments re Guaymas Sounding

“I have been noticing an on again/off again problem with the sounding at Guaymas recently and it is occasionally too wet. Today, the error was the largest yet and somehow these bad data made it into the GFS. As you can see from the attachment (see above), the GPS/IPW corrections were huge at Hermosillo and over the far SW part of Arizona. The GFS initialized Guaymas with 56mm whereas the GPS/IPW was 42mm. Yuma was 9mm too wet and Organ Pipe was 6.7mm too wet. The corrections were not applied to the WRF-GFS run from this morning, as the GPS/IPW data were delayed, causing serious havoc within the forecast.

I also looked at the NAM and its IPW field was fine over NW Mexico.

I am surprised such a large error made it into the GFS initialization. Both the temperature profile/moisture profile have a warm/wet bias. It looks to me like a one time error. There is plenty of evidence that the data made it into the GFS as there is a temperature bulls-eye over Guaymas as well as a height field abnormality.”

Mike has sleuthed this out and I am embarrassed that I got sucked-in and highlighted a bad sounding (in hindsight a PW value of almost 3 inches should have set off all kinds of mental alarms). How ironic!

Nice Morning in Tucson

After two very humid and hazy mornings in Tucson, the sky was cleaner and relative humidity noticeably lower this morning. A quick look at 24-hour changes this morning indicates that, for the southern Arizona stations, dewpoints have decreased 5 to 12F and pressures have risen ½ to almost 3 mb – neither of these trends is very exciting. However, conditions are more moist at El Paso where the dewpoint change was +9F and the pressure was up 5 mb this morning. The El Paso sounding is considerably more moist than is the very dry Tucson sounding. To our south, the Guaymas sounding (see above), assuming it can be believed, is remarkably moist with almost 3 inches of precipitable water. So, the question remains: how long will the dry out persist before the subtropical air over Mexico is pulled north across the border?

The 500 mb anticyclone again has three circulation centers – one over central California, one over northwestern Mexico southwest of Tucson, and one southeast of Brownsville, Texas. There are several weak troughs separating the centers and the most pronounced, according to the NAM, lies over northern Mexico to the south-central Gulf of California. This morning’s NAM forecast consolidates the S/W over Mexico and moves it slowly westward across the central Gulf of California. So, the convection associated with this feature may push the subtropical moisture back northward. The NAM also gradually consolidates the 500 mb anticyclone over the New Mexico/Arizona border. The NAM keeps the dry out going through this forecast cycle, but moisture will undoubtedly return sooner that the model forecasts. So, all eyes to the south for the next day or two.

Another Hazy Morning

Morning dewpoints across southern Arizona are again quite high, however precipitable water amounts are down below an inch everywhere except far southeast corner of state.
Only slight changes from yesterday when thunderstorms occurred only in far southeast.
For the fourth straight day there was no precipitation recorded at any of the gauges in eastern Pima County.

Anticyclone remains to the south but may be inching closer since winds at Tucson are quite light below 500 mb. This change in the shear may help mountain towers break through the very hostile dry air that is present above 700 mb. Sounding indicates little or no CAPE will be present at lower elevations by afternoon.

Weakening 500 mb S/W moves across northern Arizona today, with little impact down south except perhaps for some warming of the middle-level temperatures. Surge of very moist low-level air continues up the GoC and this may become important once the anticyclone moves back into the southwest US.

But for today the dry out continues.

Humid Hazy Morniing in Tucson

A push of high dewpoint surface air (see 1340Z surface chart above) has occurred over southern Arizona during the late night and early morning hours. The push has brought very high dewpoints to the lower Colorado River Basin with Yuma reaching Td of 75F. The push has gradually worked its way north during the morning. Doppler radar VADs indicate that the surge at Yuma reaches to 3,000 ft AGL with south-southeast winds of about 20 kts in this layer. At Tucson and Phoenix the layer of southerly flow extends only to about 2,000 ft AGL. With strong westerly winds above, the moisture should mix out fairly quickly this late morning.

The upper-air charts are reminiscent of late May or early June this morning and the two features of most interest are a small vorticity maximum hanging over the central GoC in the NAM progs, and a weak S/W in the westerlies approaching northern Arizona from central California. There is cooler middle-level air with this S/W, but it will tend to avoid southern Arizona where the fetch is still around the huge anticyclone over Mexico.

However, the combination of very hot temperatures, some increase in moisture, and the approaching S/W will probably lead to a bit more storm activity over mostly higher elevations across the north and east portions of Arizona today.

Another Way-Too-Dry RRS Sounding

I thought that the difference between the RRS too-dry sounding at 00Z yesterday and the GPS PW was as bad as I'd seen. But this afternoon's sounding at TWC was even worse - 0.37" for RRS versus 1 inch or so for GPS. The GPS values are very consistent around the southern part of state, so the RRS data from TWC are probably seriously in error - again, I think this is the worst I've seen.

Had a Slow Start to Our Trip

There was a serious accident on I-10 last Friday morning that closed down the interstate in both directions. Here we are in the midst of the mess. We eventually got to Phoenix after an eastward diversion through Florence. Never thought we'd be passing by the Tom Mix Memorial when we headed out that morning!

Pat Holbrook Wrote

Obviously the westerlies have had a negative impact on the monsoon and only question is when will the moisture return. The models this morning show an upper level low dropping off the west coast…quite unusual for this time of year. Synoptic systems tend to pull mid level moisture back quicker…possibly late Friday we can have enough moisture for high based storms. Low level moisture…a Saturday/Sunday morning surge is possible. Hot ‘til then.

Pat

Big Dry Out - How long Will It Continue?

Big Dry Out – How Long Will It Continue?

Today is the third day of the big dry out. No precipitation in the ALERT network on Sunday and Monday. The big question is whether or not there will be anymore precipitation in the local area before the end of July. The NAM indicates NOT.

Last night there were two large MCSs in Mexico – one peaked in northern Mexico, south of the New Mexico boot heel around 0800Z and the other is still active (see image for 1330Z above) over the southern Gulf of California. Some outflow from the northern MCS has pushed into far southeast Arizona, as indicated by the surface observations at Douglas and Rucker RAWS.

Precipitable water is down to less than an inch in southwest Arizona and ranges around an inch to an inch and a quarter over the rest of southern Arizona. In contrast, the Guaymas sounding indicates 2.1 inches this morning, so there is a very large gradient across northern Mexico.

Although the 500 mb anticyclone remains in an unfavorable location for storms, there are several things of interest in the data this morning. Surface pressures have been falling considerably over the lower Colorado River Basin – 24 hour falls of 2 to 3.5 mb from Tucson to Kingman and southwest of that line. There is a large pressure gradient up the Gulf of California and the trend should be for the higher moisture to try to come back to the north. A loop of the satellite water vapor imagery seems to indicate that this is happening.

The TWC morning sounding remains too dry, but only by about 0.3” this morning. The bad data in the lower part of the RRS soundings makes forecasting convection difficult (as per comments on last evening’s post). But, the Phoenix and Tucson soundings appear to indicate that storms are possible over higher elevations of eastern Arizona and along the borderlands this afternoon and evening. Will be keeping a close eye on the very unstable, subtropical air mass over northern and northwestern Mexico.

As Per Request

I had a request that I be sure to post the extremely bad sounding from TWC last evening, so that readers could see the sounding that went with the GPS/RAOB comparison plot in the previous post (below). The way-too-dry sounding is shown above.

VERY Bad Sounding at TWC - 00Z 28 Jul 09

Have returned home a bit ago and have been getting caught up on the weather - mostly hot while we were away, and found the rain gauge dry and dusty.

I looked at the TWC from 00Z 28 July and found that the RRS sonde performed about as bad as I've seen this evening. The sounding data indicate that precipitable water is 0.6", however, as the plot above shows, the GPS data indicate that precipitable water is actually about 1.2"! Thus, the RRS data are too dry by a factor of 2. Would imagine that this large error could have substantial negative feedbacks into models and the forecasting process.

Quick Discussion – Friday July 24, 2009

Yesterday ended up suppressed in the immediate metro Tucson area, but with storms in all directions on the higher terrain. The storm in the Computer Science web cam view above was raining lightly but producing quite a bit of lightning. Heard thunder rumbles at house from this storm. The Pima County ALERT gauge network had measurable rain at 44 of the 93 gauges; mostly those at higher elevations and those to south and west of Tucson. The morning showers yesterday, plus the abundant cloud cover, cooled the lowest elevations and keep temps down, shutting down the lower elevations of town.

The morning sounding at TWC today has the most precipitable water of the summer and most of the GPS sites in southern Arizona have 1.75 to 2.00” of water vapor. Excellent sounding for heavy rains and wet downbursts – assuming there is better heating today. The 500mb anticyclone center is far off in northwestern Colorado and the high has a very distinct, elongated south to north shape. This has allowed a significant south-southeast fetch from low latitudes that has moistened most of the west portion of the anticyclone. The NAM indicates that this will continue through about 24 to 36 hours. The NAM also forecasts the most significant storm activity today to occur out in the western portions of the state and the Rim/White Mountain country.

We’re leaving in an hour or so for four days in the Rim Country, and I won’t get another look at the charts, or be blogging, until next week. I am soaking some of the plants, for insurance, before we leave.

Very Complex Day

There was a definite up-tick in activity over southeastern Arizona yesterday. For example, 41 of the 93 Pima County ALERT stations recorded measurable precipitation. Highest amounts exceeded an inch at two locations in the Catalinas. However, rains weren’t heavy enough to produce flow in the Rillito Wash, which was dry this morning. A storm drifted south from the west flanks of the Catalinas last evening and produced lightning and thunder here at house along with a moderate to heavy shower with 0.44” of precipitation.

At sunrise this morning there were showers to south and west (one of these was over the airport producing nearly a quarter inch of rain and apparently impacting the morning TWC sounding at the University), and the skies were heavily overcast. Indeed, heavy cloud cover affects the entire southwestern 2/3rds of Arizona this morning – one of many factors complicating the forecast.

A very large MCS affected western Mexico and the central GoC for much of the past 12 hours – see the IR image from 0330Z on the blog. This event will keep moist, subtropical air flowing up the Gulf into southwestern Arizona and southeastern California. The MCS and intense activity over Mexico has apparently interacted with several weak inverted troughs, with the result that there appears to a strengthened and significant inverted trough present at 500 mb this morning – this feature stretches from just west of El Paso into the south-central GoC where there is undoubtedly a fairly strong, convectively enhanced vorticity center. The north end of this inverted trough will move westward this afternoon affecting southern Arizona.

Additionally, although the main 500 mb anticyclone has shifted inland to the Nevada/Utah border, the weak trough of the last several days over southern Arizona has managed to persist and extends from between Phoenix and Tucson westward to north of San Diego. This feature has been keeping the winds aloft light and variable; whereas, 500 mb winds at Phoenix and Flagstaff are now from the east-southeast at about 20 kt. How exactly will the wind fields aloft change today along the borderlands? The NAM keeps the speeds light as the inverted trough passes by. The NAM also moves the upper-tropospheric anticyclone right overhead by midnight so that upper-level winds decrease during the day.

Showers and convection continue to bubble this morning, particularly from the south to west of Tucson. So, convection may be quite early today suppressing afternoon heating and keeping CAPE from building to higher levels. The morning sounding was modified by the cloud and shower activity, so it is not representative of the larger environment. IF, the boundary layer mixed at 12 g/kg, with afternoon breaks in the cloud letting enough heating to occur so that cloud base was at 700 mb, there would be a moderate amount of CAPE and a substantial threat of severe storms. But, continuing cloud and early convection would mean that the day would primarily pose a threat of locally heavy rains.

Given that the inverted trough to the south will be butting heads with the middle-level high over Utah, some mix of all the above will likely occur over the south half of Arizona. Can it get anymore complicated?

Dusty Morning Skies - July 22, 2009

Dusty dirty skies at 7 am this morning thanks to the nighttime outflow from storms to the northwest - see post below. The sky at sunrise was actually quite ugly this morning - a very out-of-the ordinary situation for Arizona.

Miscellaneous Ramblings - 22 July 2009

The atmosphere in the Southwest is currently disorganized and chopped up and so will be this message.

A very nice MCS developed southwest of Phoenix last evening (as per 05Z radar image posted on blog) – I thought that this system had some potential for continuing on toward the southeast, since it obviously had a developed a nice gust front. Alas, the active convection fell apart by 07Z and all it brought our way was a dusty outflow that lowered visibilities and produced a very dirty sky at sunrise.

The really big storm activity yesterday and last night occurred over many parts of New Mexico. However, there was a severe thunderstorm out at Needles, California, and the storms southwest of Phoenix were impressive on radar. After morning showers in the Phoenix area and sprinkles here in Tucson area, the afternoon yesterday was mostly suppressed, although the morning activity damped the hot temperatures down a bit. Only 6 of the 93 ALERT gauges in Tucson area had light rain for past 24 hours – whether these amounts were from the morning activity is not clear. Other things I note this morning:

The 500 mb anticyclone is shifting inland as per models and is centered over the California/Nevada Sierras this morning, on it’s migration toward Utah. A weak secondary circulation center remains somewhere in northern Mexico. This leaves a long, curving, weak trough inside the anticyclone that stretches from eastern New Mexico westward between Phoenix and Tucson and then northwestward to west of Las Vegas. This feature is somewhat stagnant across Arizona. The two ends of it are forecast to move away from each other, leaving the feature even more washed out.

Precipitable water has continued to increase slowly over most of Arizona due to weak advection and lots of recycling by higher elevation convection into lower elevations. Phoenix appears to be in the middle of the pooled buildup with about 1.8 inches of PW – I think the highest value I’ve seen since around the end of June. The dewpoints at 850 mb at Phoenix and Tucson are at 12C this morning and there is increased CAPE available at low elevations, and it’s just waiting for a good kick.

Winds aloft over southern Arizona are essentially light and variable. The winds will be shifting to easterly directions as the high migrates toward our north, but will probably remain quite light. There is some hope that a better-defined flow field will evolve tomorrow.

Finally, surface pressures are falling fairly markedly – most stations in Arizona are down 2 to almost 4 mb during the past 24 hours and lower pressures seem to be a positive for strong storms. As for the details of what the day will bring, time will tell as the various old outflows and cloud patches interact with themselves and the terrain.

Morning Rainbow - 21 July 2009

We've had a nice cool outflow and some sprinkles this morning. The shot of the rainbow was taken at 7:30 am MST, looking from the backyard toward the west-southwest.

Morning Showers - Tuesday July 21, 2009

Regional Radar at 1400Z This Morning

Morning showers and a few thunderstorms are drifting southeastward across central and southeastern Arizona. This will certainly complicate the forecast today.

The up-tic I mentioned yesterday was mostly to west and north of the Tucson metro area. I see that Prescott and Phoenix both had thunderstorms with gusts to 55 mph and there was one severe report in south Phoenix as a large gust front headed south in the evening. Earlier, around 5 pm, a cell produced a downburst near Ryan Field, west of Tucson, that took down 20 power poles. But as for rain in the Pima County ALERT network, only 13 sites reported measurable rainfall. So, locally it was a down-tic in area coverage of storms. The Phoenix gust front came all the way south through the Tucson area, but the storms died out to the north and west of us.

The 500 mb anticyclone continues to have two circulation centers (one along central Californina coast and one in northern Mexico somewhere southeast of Tucson) with a weak and meandering trough between the centers. The shower activity this morning is occurring in this trough zone. The NAM indicates little change through tomorrow and then shifts the California center inland and northward so that at 84 hours there is a single 500 mb anticyclone over Utah. Winds aloft remain weak and the trough over Arizona does not link with a stronger S/W coming south – so the situation over Arizona remains pretty stagnant next couple of days. There’s enough moisture for daily storms but not enough for really serious amounts of CAPE except in mountains.

From today’s NWS Tucson early morning Forecast Discussion: “LIKELY THERE WILL BE CONVECTION SOMEWHERE IN THE CWA EACH DAY...BUT COVERAGE AND INTENSITY WILL BE DETERMINED BY MESOSCALE FEATURES ROTATING AROUND THE UPPER HIGH...UNRESOLVABLE MORE THAN ABOUT A DAY IN ADVANCE.”

What more can I add, except that I’m certainly grateful that I don’t have to do a deterministic forecast for each the next seven days!

Jim Means Wrote:

Respectable convection finally made it closer to my area yesterday. NWS San Diego issued a severe thunderstorm warning late Sunday afternoon for a storm with radar-indicated 1.25" hail in the Anza-Borrego state park region. Things seem primed for a repeat performance or better today with deep moisture continuing over the area plus a nice gulf surge up the Imperial Valley. 10 am dewpoints are in the mid- to high- 70's (98/78 at El Centro, 99/75 at thermal).

Jim
Alpine, CA

Rob Kursinski Wrote:

We drove through a lot of blowing dust on the way back from Phoenix to Tucson between 7 and 8 pm last night. At one point several cars pulled off I-10. We found puddles of water in the driveway when we arrived but the portable basketball hoop didn't get knocked over like it had Friday.

On the RRS sonde problem, note also that the RRS is typically (but not always) drier than the GPS PW values which will lead to a systematic underestimate of precipitation. (Remember the good old days when the sonde and the GPS agreed to 1 to 2 mm except when there was a thunderstorm over one but not the other.) As I noted to Mike Leuthold the other day, in our paper in the NAME dedicated CLIVAR issue from April 2008 I think, when conditions are near the edge of triggering deep convection, the amount of rainfall (iat least in the virtual reality of WRF) is very dependent on the initial PWV. For the wetter of the two days we examined, the sensitivity in the southern Sonoran region was such that once the minimum amount of PWV was exceeded for deep convection, adding 1 mm of initial PWV increased the average rainfall over the region by 6 mm (!).

Another interesting point, Carlos Minjarez noted yesterday is that while Sonora has been getting some impressive MCSs, Hermosillo has actually gotten very little rain so far.

Monday Morning - July 20, 2009

There were a surprising (when one examines the CAPEless TWC 00Z sounding) number of thundershowers around yesterday afternoon. Before 5 pm, 7 of the 93 ALERT gauges in eastern Pima County had recorded light amounts of rain. After 5 pm an additional 21 gauges had light rainfall from the thunderstorms that were drifting around. All amounts were less than a quarter of an inch, except for 0.55” at Florida Canyon. Here at the house there were several rumbles of thunder after 4:30 pm and the afternoon showers left 0.02” in the gauge, but another shower must have come by after dark, since there was 0.10” in the gauge this morning.

Precipitable water has inched up some and there is a distinct nose of higher values out to the west in the lower Colorado River Basin – values are around 1.5” in west and around 1.25” in the Tucson area. The morning TWC sounding agrees well with the GPS PW (for first time in quite awhile) this morning and indicates that there’ll likely be more CAPE available for afternoon storms today, and the NAM indicates this also.

The large 500 mb anticyclone that covers all of the southwest US has two separate circulation centers this morning – one over the central California coast and one over northern Sonora. The second center is bringing usually hostile west winds across southern Arizona, but speeds are light and there is higher moisture to the west and southwest. The NAM keeps the two circulation centers through tomorrow, with a weak trough between them. Flow in the upper-troposphere appears to be difluent over southeastern Arizona. The model forecast then brings a shortwave trough down the east side of the 500 mb ridge that affects New Mexico and Arizona – if the model forecast verifies, conditions for strong storms will be more favorable Wednesday and Thursday.

Today looks much like yesterday, but probably with an up-tic in storm coverage and rain amounts. The plot at top of this post illustrates that GPS PW values have been different than TWC sounding PW amounts for most of the past five days. This uncertainty in the RRS sonde data exacerbates an already difficult, summer forecasting situation.