Some Promising Signs

I see that the Tucson NWS forecast this morning calls for 10% POPs each of the next 14 forecast periods (i.e., 7 days). This implies that there is not enough information contained in any of the model forecasts to discriminate between essentially peristence and the evolution of the day-to-day weather. Since my outlooks have been called dismal of late, I'll try to read something positive between the model lines this morning.

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First a look to the south - the southern GoC has been affected by dissipating MCSs the last two mornings, and this morning there is what I call a "north-racer" at the southern end of the Gulf (see top image). These occur several times each summer and race to the north, hugging the eastern coast of the GoC. Once in a while they persist all day long. The middle, satellite image shows that cloud debris has poked northward toward southeastern Arizona and now extends to north of 30 degrees. The soundings at El Paso and in northern Mexico this morning show northeast to east steering winds and have substantial CAPE - thus, the MCS activity should shift northward today and tonight. All of this favors an eventual push of the subtropical air into southeast Arizona. The 500 mb pattern remains pretty dismal overhead today and the 200 mb chart (bottom) certainly looks like fall, but there'll be a good, vertical, wind-shear vector in place when the moist air pushes in beneath the westerlies. Tucson's sounding exhibits a bit more CAPE today and there is nice layer of southerly flow around 700 mb. Thus, I'd expect an upturn in storm activity this afternoon and possibly again tomorrow.

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The NAM forecasts this morning continue to indicate an inverted trough(s) at 500 and 700 mb moving across, or perhaps stringing out over would be more accurate, northern Mexico. These features, along with the increased MCS activity in Mexico, should act to push the subtropical, low-level air northward, leading to a real upturn in storms and their intensity by Saturday evening. Tomorrow's situation will depend upon the evening and nighttime storms and outflows that develop today, particularly over northern Mexico and the Borderlands. So there are some features of interest to keep an eye on as the weekend approaches!

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Finally, a brief summary of yesterday. Activity was down some and almost no gauges in all of southeast Arizona caught any measurable rainfall. I found only two gauges of the 93 gauge ALERT network with rain (0.24" at Brawley Wash out to the west). Indeed the cells out to the west of town produced a number of lightning strikes, and I got the slightest bit, not even enough to be called a spit, of a sprinkle from one of the anvils here at house. Thunderstorms, but no rain, were reported at Douglas, Ft. Huachuca, and Nogales.

Bit More Moisture Continues in Lower Half

Rainfall occurred yesterday afternoon before 6 pm at 3 of the 93 ALERT stations, at 2 of the regular NWS reporting stations (Nogales and Ft. Huachuca both with thunder) and at 4 RAWS gauges. Amounts were less than a quarter of an inch, except for 0.35" at Empire Peak.

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The increase in PW noted yesterday afternoon continues today in the lower half of troposphere with values in south-central Arizona generally 35 to 40 mm, and Yuma is also up considerably from past days. The morning sounding at Tucson (top) shows more moisture below 450 mb but also a nasty inversion at the interface to the warmer dry air above. There's a nice little slug of CAPE below 450 mb but probably not enough to overcome the inversion, except perhaps over some of the mountains. The large-scale setting remains dismal with the 500 mb, west coast trough (middle) well inland and forecast to push toward the northern Plains the next couple of days. The 250 mb jetstream (bottom) will become more westerly and be very far south for August (near the Four Corners). The NAM model continues to forecast afternoon showers over the higher terrain of southeast Arizona for rest of week. Tropical Depression Five-E is forecast to become a TS and move ashore east of New Orleans. A remnant inverted trough from the TD may head westward across northern Mexico this weekend.

Nice Upturn in Storms This Afternoon

Well there has been a nice upturn in thunderstorm activity this afternoon - proving that one should never let their attention lag, as I did this morning. Two important things have transpired - higher maximum temperatures, along with increased PW, have led to increased CAPE and more storm activity. Since lower-level winds are mostly zilch, the increase in PW (see top image of GOES PW this afternoon) is mostly due to recycling and heating. The middle image shows CG lightning detections around 3 pm this afternoon - a very definite upturn in thunder and lightning - and bottom image shows latest visible staellite image indicating lots of storms back into Pima and Santa Cruz Counties. So it goes.

Very Suppressed

Little in the way of weather to report across Arizona yesterday. Five stations in the Pima County ALERT network measured rainfall (0.04" at 4 of these and 0.16" at one) in the 6-hours ending at 6 pm, and that was all I could find across all of southeast Arizona. Ft. Huachuca and Douglas did report brief thunderstorms with no rain. Cloud-to-ground lightning strike loops indicated a few strikes (looked like less than 10) over Cochise County in the late afternoon - no CGs indicated in Pima or Santa Cruz Counties. Skies are clear this morning. Precipitable water values in south-central Arizona are around 28 to 29 mm and a pocket of higher dewpoints remains present over the southeast part of state. The sounding from SPC (top) indicates small amounts of Tv CAPE today. Winds aloft are southwesterly through the entire troposphere above 700 mb. The 500 mb analysis from NCAR RAP (middle) shows a large anticyclone over the country with the main center far to the east over the Tennessee Valley and a secondary lobe centered near Brownsville, Texas. This secondary lobe is forecast by the NAM to shift rapidly westward and to be nearly overhead by 5 pm tomorrow. This morning's run of the NAM forecasts some isolated showers again today over southeast Arizona (bottom) - so continuity appears to be a reasonable forecast. Nothing of real significance appears on our horizons at this time.

Looks Like September

The new week starts out looking much like we're in a September transition pattern, with a 500 mb (see middle panel from NCAR RAP) trough over the west, strong shear, and some left-over subtropical moisture. The morning TWC sounding (see top panel from SPC) shows some CAPE for the surface lifted parcel, but only a small sliver of afternoon CAPE seems likely. Further, the upper-level warm air will probably strengthen some during the day. There may be some low top showers around again this afternoon, but overall the situation appears more hostile than yesterday and yesterday was pretty dismal.

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This morning's NAM forecasts indicate that the mid-upper level anticyclone will rebuild over northern Mexico and the Borderlands and become quite intense by the middle of the week. The bottom image shows the NAM 500 mb forecast valid Wednesday afternoon, with the 500 mb high centered just northeast of Tucson. Again, not very promising. However, the next few days should certainly allow the atmosphere to cook and to restablish a hot, deep desert boundary layer.

Yesterday - Few Showers No Thunderstorms

The last three days certainly did not pan out as per the optimistic forecasts, driven by the NAM, starting about the middle of last week. The exception was western Cochise County which appeared to be pounded by a number of very intense storms, especially Friday and Saturday.

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Yesterday's U of A Atmo WRF runs were excellent, showing about 10 to 20% coverage of mostly light and some moderate showers. This is exactly what the observations show happened - about 10% coverage of light showers yesterday up through 00Z (see above satellite images) and about 20% coverage after 00Z through the evening, with some moderate showers mostly over the Catalinas, with several ALERT gauges reporting just over a quarter of an inch. There were no CGs detected in all of southeast Arizona as far as I could tell, and the showers had slight VILs and tops in the 20 to 30 thousand foot range - this fits with the two satellite images above - the visible (middle) image shows showers from central Pima County eastward; but the water vapor image (top) indicates that most of these showers weren't deep enough to be detected in upper-tropospheric water vapor data. I missed my guess yesterday that the demarcation line between showers and no showers would be nearly overhead - so it goes in summer forecasting.

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Finally, the TWC sounding last evening at 00Z (bottom image) was clearly garbage, due to a shower, but was transmitted regardless, and will lurking out there in the data archives to foul up future research.

What Will Today Bring?

The forecast for today is quite tough, and has a very bimodal, yes or no aspect to it (I'm writing this a bit before 8 am). The upper-tropospheric air is very dry overhead, with a very sharp boundary between the Pacifc dry and the subtropical wet air masses. The top image shows the water vapor satellite data with the dry boundary (upper level dryline if you will) just off to the east of Tucson. The middle image shows the morning TWC sounding - if things were static, then this sounding should easily supprt deep convection fairly early as heating commences (it's quite clear here and to the west). However, the GPS PW data indicate a very strong gradient in PW from Tucson westward. Current PW values are: Safford 42 mm; TUS 33 mm; PHX 33 mm; Tohono O'odham CC 26 mm; Organ Pipe NM 24 mm; and Yuma 19 mm. So, if the winds pick up a westerly component below 500 mb there will substantial drying from west to east - somewhat like a Great Plains dryline. Where will the demarcation be between storms and no storms? At this time I'd have to guess, based on the NAM forecast winds and the strong drying trends in the GPS PW here and to west, that storms later today will occur primarily east of Tucson.

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Note that in the longer term the ECMWF has been advertising a significant dryout for the first part of the coming week. However, the NWS models seem to be forecasting that the 500 mb anticyclone will prevail and push the west coast trough back out over the ocean - so something else to watch. Finally, note that Tropical Storm Estelle is southwest of Baja moving west and will not be a player this far north.

Quick Summary Yesterday and Last Night

Here at house there was a light sprinkle around 7 pm last evening - I then checked rainfall reports around NWS Zone 33 and found that 4 of 93 ALERT gauges had had very light amounts during the day yesterday. Thus, as per John Diebolt's comment immediately below, the POPs for yesterday were not good and way too high.

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Some thunder, lightning and light showers began here at house around 9:30 pm and lasted until a bit before midnight. The nighttime amount here was 0.29"; the airport had no rain yesterday or last night; DM had 0.02" last night; and U of A Atmo had 0.24" last night. The ALERT network showed that 64 of 93 gauges in Zone 33 had rainfall last night - so, the POPs for last night were quite good. There were a few amounts of around an inch, but most amounts were not very great - 1.26" at Pima Wash and Ina was the max amount from the network. Radar and IR satellite images are shown above for 11 pm last evening.

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Definitely a very mixed bag locally both Friday and Saturday.

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Added Sunday afternoon - Jim Toth reports on rains at his place (a bit to the northwest of here):

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Last night I got 0.86 inches, which I see is more than you for a change. It started about 9:10 PM. About 0.66 had fallen by a little after 10 PM. There were several complete stops and restarts, which gave the impression outside in the dark that cells were rapidly traversing from the south. But from brief glimpses of TV radar, they must have been back-building. It was still going off and on when I fell asleep about 11:30.

Until last night, my largest amounts for the summer had been 0.54 the night of July 19 (on the southeast fringe of the big dump around Westward Look) and 0.44 the night of Jul 29. So I had only about 1.15 for the entire month of July.

Quite Messed Up Setting Today

The early morning rains have left behind a messy synoptic situation for Arizona today. The 500 mb vorticity maxima that yesterday's NAM made an important player for today has vanished and been replaced by a new convectively-induced vortex that is situated just off to the east of Tucson. The visible satellite image (top) shows that all of Arizona was covered by heavy cloud at sunrise, and that a nice slug of moisture will be moving into Utah later today. Much of northwest Mexico has cleared out though, and this will essentially be the wild-card in how today's weather evolves over southeastern Arizona. The large clear area over northwestern Mexico is exactly where this morning's NAM has initialized a large moisture maximum at 700 mb, leaving the model starting out with a dubious analysis.

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The morning Tucson sounding from SPC (middle graphic) indicates no CAPE and is of an onion character, having been highly modified by the MCS debris and light rain. This sounding, with heating later today will have to build a new boundary layer surface upward. The sounding will develop some CAPE but will require a good outflow kick to release the CAPE - thus the important question of what will develop over northern Mexico and Sky Islands of southeast Arizona. The SPC had outlooked a very large area with a risk for severe thunderstorms today, but the latest update has wisely dropped that. However, things could become interesting later today in the Canyonlands of Utah and perhaps along the Borderlands. Winds remain mostly south-southwesterly with some speed shear in upper-troposphere; the sounding's north-northeasterly winds around 700 mb reflect the convective vortex to Tucson's east. Today's NAM forecast for precipitation ending at midnight tonight (bottom graphic) has become a mere shadow of what it was forecasting for this period the last several days - so, we'll have to watch carefully how things evolve later today, and I look forward to seeing what the WRF runs come up with this morning!

Storms Mostly Elsewhere Yesterday

While there was a bit of an uptick in rainfall coverage yesterday, amounts were mostly light and heavy storms occurred generally far off in the distance from the Tucson area. I did note several very strong storms that essentially stayed locked in place for several hours. One was near Ash Canyon and the other was off on the northeast flanks of the Catalinas. These storms tried to move north, but their anvils were stabilizing that path, and they built new cells on their south flanks, essentially moving little. In the ALERT network 44 of 93 stations had measurable rain, but amounts were light, with two mountain sites measuring a bit less than half an inch. However, right in the middle of town one gauge, Kolb and Golf Links, reported 0.98" - I don't know whether this is a gauge problem or if there was a local cell that dumped on that gauge. Here at the house we had light anvil rain, from the decaying MCS in northern Mexico, during the early morning hours - total of 0.05". The largest 24-hour rainfall total I could find in a quick look this morning was 1.33" at Columbine RAWS on Mt. Graham.

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The images above show two MCSs in northern Mexico at 0330Z, a large and strong MCS remaining at 0600z, with anvil cloud extending northward over much of southeast Arizona. The concurrent regional radar image (bottom) shows little in the way of hard convection. New and fairly strong storms developed after midnight off in northwest and west-central Arizona - much as forecast by the WRF-GFS model run of yesterday morning.

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John Diebolt left an excellent comment last evening anticipating both the debris rain this morning and the forecast issues for today:

I was looking forward to the first good night for lightining photography Friday evening.. Was out on Ina/Wade focusing on storms over the Catalinas and Oracle Junction. I got one bolt before the towers collapsed. Got home to look at Radar around 8:45PM with a complex moving west across Sonora and had these thoughts: Ordianarily might see a scenario this weekend where this complex over Sonora clouds us over and outflow generates some precip overnight/early morning leaving us very moist but lacking for solar insolation Saturday and relatively down. Sunday as southwesterlies begin to develop..action focuses just e/ne of Tucson and moves off to the NE with little development upstream to the SSW/SW and the result being many valley locales miss the action. The trough dynamics nearby this time around could make all the difference, overcoming our usual quandry in high-moisture situations. Plenty of opportunity to bust a high PoP forecast this weekend! From my limited time in Tucson (6 years) it seems it takes an exact mix of everything to generate a widespread precip event and if anything is the slightest bit off..it fizzles. The vagaries of monsoon forecasting... bad sounding data..lack of Mexican data. Not the most enviable job but challenging!

Very Complicated Situation Today

Brief overview of the situation today follows:

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Sounding at Tucson this morning (top) indicates little to no CAPE; as did the sounding last evening before the thunderstorms at the airport. However, wrt GPS PW the sounding last evening was over 1 cm too dry and this morning's sounding is a bit more than 5 mm too dry. So, throw out all those indices computed by the sounding analysis software. There appear to be enhanced southeast winds at low-levels (both Tucson and El Paso) affected by both outflows and a decaying, backdoor front to the south. The Guaymas sounding this morning has moistened nicely and shows a good surge signal, enhanced by very strong outflow from the strong MCS that collapsed just to the south this early morning, in low-levels. Around the area, GPS PW values are: Yuma 19 mm; Tucson 32 mm; and Hemosillo 51 mm. So, highest moisture values extend northward from GoC into southeast Arizona. The vertical wind profile is not great for organized storms with winds from 600 mb up being from the south-southwest at 20 to 30 knots, indicating that anvils will try to spread out directly ahead of storms. this is a poor profile for rainfall in this part of town - unless, as I noted below, something develops very close to the south. Convective cloud bases indicated around 600 mb or so, with threat of gusty winds remaining because of the deep, hot boundary layer.

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At 500 mb, the morning NAM analyzes (middle graphic) a nice inverted trough over the southern half of GoC, with a convectively enhanced vorticity maxima (see IR image of MCS activity over south GoC at 08Z this morning) southwest of Hermosillo. The Pacific trough remains along the California coast, and the center of the 500 mb anticyclone has slipped just south of the border in the Southwest. Further south, TD Seven E is spinning fairly vigorously south of Cabo Correntes - this system is forecast to become a TS and to move off to the west, passing southwest of the end of Baja. Many aspects of the current setting look like it's September rather than early August.

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The NAM appears to forecast an afternoon and evening similar to yesterday and holds off the increased moisture and heavier rains until tomorrow. I'm inclined to think that better moisture may be in southeastern Arizona by evening and that there should be another increase in activity relative to last two days. However, the details of today are complicated by the cool outflows that have affected the area, and by clouds and even some midmorning storms. Thus, a very difficult day to forecast for specific points.

Second Day With Increased Storm Activity

Storms and rainfall increased yesterday, relative to both Wednesday and Tuesday (Tuesday was nearly completely suppressed across southeast Arizona). All of the NWS reporting stations in the southeast reported storms and light rains (less than 0.10" except for Safford which measured 0.46"). Several stations reported gusts of 30 to 45 mph and the anemometer on the roof at Atmo on campus measured a gust to 62 mph as a large, mesoscale outflow moved northward across the metro area. Here at the house we had nice views of storms, mammatus, lightning to south, and a double rainbow, but not even a trace of rain. Southerly flow in upper-troposphere is not good for here unless something develops nearly overhead.
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Across the Pima County ALERT network 14 gauges had measurable rainfall. These were mostly in the south part of the network. Amounts were again mostly quite light. The most I saw reported was 0.43" at the Summit Elementary gauge. The higher elevation RAWS gauges in southeast Arizona had rain at 6 sites, with 3 of these having more than 0.50"; Empire getting the most rain with 1.09".

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Photos above - taken yesterday evening - show mammatus to the southwest and double rainbow on the storm to south near the airport. The bottom image shows lightning CGs detected around 6 pm with a nice cluster of CGs near the airport.

Several Interesting Days On Tap

YESTERDAY - Thunderstorm activity increased yesterday afternoon and evening - particularly in Cochise County, where there were several special statements issued by NWS for heavy rains and flooding. One station in the ALERT network (Haystack Mountain) reported 0.14"; Ft. Huachuca reported a thunderstorm and 0.37"; and the RAWS at the Headquarters of Chiricahua National Monument reported 0.71". Precipitable water remains around an inch or so at lower elevation stations, so the main driver for the increased CAPE was the ongoing heat-up of the boundary layer and a bit of middle-level cooling. Pat Holbrook noted early yesterday that: Bob, Both GFS and NAM showing a surge this weekend...maybe as early as saturday. Nothing on GYM sounding today so it won't be tomorrow. Pat
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TODAY - Yesterday's discussion still relevant. Surface pressures are falling nicely as the heat-up continues - 24-hour pressure falls this morning over the lower Colorado River Basin are 2.5 to more than 3 mb. Thus, the up-gulf pressure gradient is likely increasing, as is the gradient for middle-level southerly flow. The deeper, subtropical moisture appears to still be over south half of GoC. The Guaymas sounding seems to show a very shallow surge signal this morning and an MCS dissipated over the southern GoC late last evening (see top IR satellite image). The Tucson and Phoenix soundings appear to have a tiny sliver of CAPE, so thunderstorms will again tend to be over higher elevation areas this afternoon.
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NEXT COUPLE OF DAYS - The 500 mb trough along the California coast and the anticyclone over the Southwest do battle and keep an increased gradient for southerly flow through the weekend. The model forecasts agree that the deeper moisture flows northward into the Southwest after 60 hours, with a significant increase in storms and rainfall. The current NWS forecasts indicate 50% POPs for lower elevations in the Tucson area all day Saturday. The NAM forecast from this morning (bottom image) indicates widespread precipitation for the 60 hours ending at 5 pm Sunday afternoon. So looks like interesting weather changes through the weekend.

Interesting Forecast Discussions (FDs) From NWS Tucson

My only comment on these excerpts from recent FDs is that they have an aura of revisionist history to them (highlighting added):
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At 2 AM Wednesday August 4 - …MORE STABLE ATMOSPHERE THAN ONE MIGHT NORMALLY SEE IN EARLY AUGUST MOST YEARS. ANOTHER DOWN DAY OR TWO IN THE WORKS BEFORE THE….
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At 902 AM Wednesday - …THIS WILL LIKELY BE THE QUIETEST DAY OF THE WEEK WITH OUR BRIEFLY HIGHER DEWPOINTS THIS MORNING QUICKLY FALLING INTO THE 40S THIS AFTERNOON.
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At 255 PM Wednesday - …HAVE HAD A FEW MORE TSTMS THAN EXPECTED OVER THE FAR E CWA TODAY. TO MY MILD SURPRISE….
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At 830 PM Wednesday - …IT WAS A MORE ACTIVE AFTERNOON AND EARLY EVENING THAN EARLIER EXPECTED ACROSS MUCH OF COCHISE INTO SOUTHERN GRAHAM COUNTY AS SHOWERS AND THUNDERSTORMS DEVELOPED FIRST OVER THE MOUNTAINS AND WHILE THEY INITIALLY STRUGGLED IN LOWER ELEVATIONS THEY WERE LATER ENHANCED BY OUTFLOW COLLISIONS. THIS RESULTED IN SOME STRONG THUNDERSTORMS WITH LOCALLY HEAVY RAINS NEAR PEARCE-SUNSITES AND MOST RECENTLY NEAR SIERRA VISTA.
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At 2 AM Thursday - ….AS EXPECTED THUNDERSTORMS STARTED TO CREEP BACK INTO THE PICTURE ACROSS FAR SOUTHERN AND EASTERN AREAS THIS PAST AFTERNOON AND EVENING……

July - A Wet Month For Flagstaff

David Blanchard reports:
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July summary for Flagstaff: 5.94 inches at the airport (4th wettest July on record).
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14 days with 0.01" or more.
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9 days with 0.10" or more.
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3 days with 1.00" or more.

Discussion Wednesday Morning August 4, 2010

Conditions continue quite dry over southern Arizona and northwest Mexico with PW values ranging from the upper 30 to lower 40s of mm. The TWC sounding (top image from the SPC) now indicates some decent southerly wind speeds below 500 mb, as the anticyclone strengthens over the southern US (see middle and bottom analyses from NCAR RAP). So, even though we remain in the flow regime of the US lobe of the Atlantic subtropical high (at least in lower-half of troposphere), the atmosphere is relatively dry. At 500 mb, the weak deformation zone remains over the lower Colorado River Basin, separating the flow around the Atlantic and Pacific subtropical anticyclones. The Pacific trough is forecast to take over this zone, a bit off the coast, as the 500 mb high strengthens and shifts westward. Note that in the upper-half of the troposphere the flow (see 250 mb analysis) has a fetch through the Pacific trough (at least over most of Arizona) and is not part of the subtropical flow regime - in the past, I've referred to this type monsoon flow setting as being mixed mode, i.e., about half subtropical and about half westerlies.

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As the lower troposphere heats up today and tomorrow, I think we can expect upticks in thunderstorm activity each day, especially over the mountains. Although the flow is becoming more southerly, deep moisture remains quite far away - so initially, the development of increased CAPE will have to be due primarily to heating and related moisture recycling from the recent heavy rains.

Visit To Ash Canyon

We visited Art Douglas at his new house in Ash Canyon yesterday (Tuesday August 3rd 2010). Ash Canyon is in the southern Huachuca Mountains, south of Sierra Visita. It was green and very damp and even a bit humid yesterday, when most of southern Arizona had dewpoints that dropped into the middle 40s. Top image is looking, from a second floor balcony, west-southwest up Ash Canyon. Middle image is of Art standing by his weather station. We drove up Carr Canyon Road in the afternoon, passing right by the Carr RAWS station. Bottom image is from a viewpoint on that drive. The isolated shower was over the east side of the San Pedro Valley and was taken looking toward the north-northeast. Hard to turn off the summer showers completely down in that area - definitely a very much different climate zone than here in the Rillito Bottoms! So, when Art reports in with observations from Ash Canyon, this is where he's coming from.

Drying Across Southeast Arizona

Top image shows a nice view of Catalinas with good visibility and only mare's tail cirrus clouds present. Significant drying has filtered into southeast Arizona during last 12 hours or so, both from the Pacfic and from northwest Mexico. The TWC sounding (middle image from SPC) indicates little to no CAPE, and has dried considerably at mountain-top levels also. The bottom image from the RAWS station up in the Rincon Mountains shows a time series of T, Td, and RH, with Td dropping steadily since late yesterday. So, even through southeastern Arizona will remain predominantly under the influence of the 500 mb, subtropical, anticyclone for next several days, there is not much weather in sight, except perhaps for some isolated mountain storms.

Brief Summary of July and Misc.

July 2010 Summary - Here at house rainfall totalled 3.26" - making it the 5th wettest July of the 12 years I've kept records. Rain of 0.10" or more fell on only 4 days and the bulk of the monthly total occurred on two days - the 29th and 30th. Thus what was mostly a very hot and dry month ended up wet. Shrubs and plants are quite happy with the soil moisture and higher humidity. Shown in top image is a Texas variety of purple sage. Mexican rain lilies are also bursting into bloom after the rains.

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At TUS rainfall was 2.71" (the 36th wettest July since records were kept here); again with the bulk of the rain falling on just two days. PHX at Sky Harbor ended up with 1.97" (the 13th wettest July on record there); with virtually all of the rain falling on the last two days of the month. Out in Yuma, July brought a only a trace of rain; tied with other Julys having no measurable rainfall. So this month, particularly at low elevations, illustrates well the vagaries of daily weather within the highly variable desert climate regime.
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After the wet ending of July, southeast Arizona was very suppressed on Sunday the 1st, with a slight uptick late yesterday on the 2nd. See bottom two regional radar charts from NCAR RAP.

An Ill-Fated Morning For Blogging

We have had two separate power outages that have taken my system down this morning.
The second came just as I was completing four paragraphs; so, not a good start to day.

Readers' Digest Condensed Book version:

- Very suppressed yesterday as per excellent U of A WRF model forecast.

- Weak flow and weak inverted trough remains stretched across Arizona from SW to NE -
dominant players in local storms next several days - local moisture/CAPE; sunshine; and
orography. Best chances at high elevations where there's more CAPE,

- Dry low-level air from off Pacific continues sloshing around, affecting CAPE - mostly to west but
it can be seen in the am Tucson sounding; which has little or no CAPE unless the dry air moves away.

- Atlantic TD4 has formed.

Continues Quite Moist But With Stagnant Winds

Heavy cloud cover prevailed over much of the region yesterday and, with diminished CAPE, made for a much less active day. Rain occurred at 54 of the 93 ALERT gauges with amounts quite light at lower elevations and with great amounts in the Catalina and Rincon mountains areas. Max amount was 1.18" at Dodge Tank on north side of the Catalinas. Here at house we had several spinkles and end the month with a trace - the 29th and 30th events, however, turned what was mostly an extremely dry month into a wet month with 3.26" of rain here at house.

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High temperature yesterday was a cool 81F and today starts with heavy cloud cover, except over in Cochise County - see the top two images. The sounding at TWC this morning indicates moist conditions (PW are in 40 to 50 mm range at lower elevations) but with little CAPE and light/variable winds through much of troposphere. The morninig NAM continues the weak flow situation for the next 24-hours and keeps most rainfall at higher elevations.