Just Back From Sonoita

We have just returned from 5 miles NW of Sonoita, after driving down there late yesterday afternoon. So, I have several things to catch up on.

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I goofed up on Pat Holbrook's message about his GoC surge forecast message - he anticipated a surge by tomorrow morning (the 11th not the 10th) - sorry that I reported this wrong. Given the large MCS approaching the middle GoC this evening (bottom image), and after the one last evening further south, I'd say it's a gimme!
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My forecast of deeper, colder storms over the mountains yesterday afternoon busted badly - looks like I forgot to account for the advection and mixing impacts of the strong mountain-top estaerly winds that continued through the day yesterday - always something jumping up to bite you.

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Driving down to Sonoita on 83 last evening there were several light to moderate rainshowers - saw no lightning.

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Early afternoon down there today observed my first thunderstorm of the 2010 summer season - couple of long rumbles (didn't see any CGs) from a storm on the northeast flanks of Mt. Wrightson. Light showers down there most of afternoon and much of return drive - but little in way of accumulations. Gauge here was dry but had some dead insects in it as well as bird droppings; so I cleaned it out in hopes for tomorrow.

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Top photo is a nice sunset last evening (Friday Jul 9 2010) looking northwest at the north end of the Santa Ritas. Middle photo is rainshower (no lightning observed) south of the santa Ritas.

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Noted a new fire burning in the eastern Catalinas on return - assume it was started by a CG?

Weather Discussion for 9 July 2010 - Southeastern Arizona

Brief summary of yesterday – bit more measured rainfall at high elevations yesterday from the mostly warm-top convection. The Pima County ALERT network had rainfall measured at 8 of 93 stations with 2 stations reporting slightly more than a 1/10^th of an inch. Three of the RAWS stations had rainfall, with Columbine on Mt. Graham reporting 0.17”. Of interest was the occurrence of deep, cold-top convection further north in Mexico, with convective remnants dissipating over the far southern GoC during the night.

This morning – considerable cloudiness extends far to the west and into southern California. Easterly low-level winds continue, but there is a nice layer of south-southeasterly winds above 800 mb (see TWC sounding plot – note sounding is a bit dry [2.5 mm] wrt the GPS data) and these have acted to increase moisture substantially from 800 to 500 mb – quite an interesting change since yesterday morning. Dewpoints have increased 3 to 5 degrees F at the mountain top RAWS stations during this period, which is quite important. GPS data indicates that PW has reached values above 30 mm (see lower image) across southeastern Arizona this morning – which is also a positive factor. The westerly Pacific jet in upper-troposphere has shifted northward, leaving winds in southeastern Arizona L/V above 600 mb. It appears that convection will have some westerly component to its steering flow, at least through much of day (the morning NAM tries to bring this around to easterly by midnight). On the downside is the fact that the warm inversion aloft has strengthened some this morning – it is quite formidable in the sounding plot!

This afternoon and evening – looks like a definite continued upturn in convection today. The big question is whether we’ll see the development of deep, cold-top storms. This looks tough for the low elevations, unless some very strong outflows develop. However, conditions over the mountains are much improved today. I can come up with lifted parcel theta-w of 24C and possibly greater for the higher mountains, meaning there’s an excellent chance for much stronger, cold-top, storms over the mountains. Should be a much more interesting afternoon and evening, with better chances for strong outflows into lower elevations. To the south, the upper-level inverted trough will be moving across the lower half of the GoC, with a significant increase in strong convection in Sonora and Sinaloa. Pat Holbrook e-mailed yesterday that he thought there’d be a Gulf surge tomorrow. Given the likely increase in storms over and near the GoC next 24-hours, I think that he’s probably correct. Perhaps I’ll record the first rainfall of the summer here at house by Sunday evening – chances are certainly looking good.

Warm Air Aloft Dominates Today

The warm air aloft discussed in this morning's post essentially won out during the day today. The top image is the visible satellite image this evening, showing widespread convection of a moderate nature. Note that there are no anvils spreading out in the stronger upper-level winds. The middle image is the WSR-88D echo top product and it shows that radar echoes in southeast Arizona this evening are reaching only to max heights of 25 to 30 thousand feet. The bottom image is the WSR-88D Vertically Integrated Liquid (VIL) product. The values of current convection are VERY low, indicating that there is little rainfall reaching the ground at this time. Hopefully things will improve markedly during the next three days!

Many Similarities To Last Week Continue

First a quick summary of yesterday - weak storms on mountains with limited outflows and not much rain. Convection was not very deep yesterday - just deep enough to generate some CGs at higher elevations. Very deep convection was limited to areas well east of Continental Divide and in Mexico south of about 27 degrees north (i.e., not very close to our area). I examined all the reporting stations, RAWS stations and ALERT gauges across southeast Arizona and could only find: a trace at Douglas, 0.01" at Trail Cabin, and an unknown but measurable amount at Safford. So, not much activity for a day in July.

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Lot of things coming into play today make for a complicated forecast. Low-level moisture has increased from the east (as per a week ago there is a strong gradient from Tucson to El Paso with much cooler and more moist air on the east side of Continental Divide - see satellite image above). TD-02 is near Brownsville, Texas, a bit further north than was Alex. There is a pronounced upper-level inverted trough ahead of TD-02 but morning NAM indicates this feature will be squashed to the southwest, leaving the best upper-level difluence back in west Texas and southeast New Mexico. The current NAM forecast indicates that TD-02 will persist and make it into southeast Arizona by Sunday as a much weakened feature within the building ridge. Thus, the subtropical moisture with TD-02 is forecast to eventually come across the divide. Low-level flow is again this week fairly strong and downslope which is a negative.

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The morning TWC sounding (lower image) has moistened considerably during past 24-hours, from the east, and is once again approaching PW of 30 mm. The TWC data and the GPS data are within a mm or so on PW this morning, with TWC just a bit more moist. Offsetting the low-level moistening is a deep layer of very strong warming from 500 mb to 300 mb, with the temperatures around 400 mb having increased more than 5C. Thus, even with increasing moisture during the day, it appears that low-elevation CAPE will be quite limited - a forecast cloud base of 600 mb with theta-w of 22C has only a small area of CAPE from 600 to 450 mb. So, it is likely that only higher elevation convection will have much hope of beating the warm air aloft, since I don't see any indications of cool advection in the upper-half of troposphere.

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So a considerably mixed bag of pros and cons for today. However, we can hope that TD-02 will come closer to us than did Alex and bring improved chances for rain over the weekend. The upper-level inverted trough may also invigorate more intense convection further north in Mexico, which could help push low-level moisture up the GoC.

Hot And Dry

Mostly a suppressed day, with some light storms on mountains. Dewpoints were running 30s to 40s over almost all of south-central and southeastern Arizona at 5 pm this afternoon. There were a few lightning strikes as close as off to the northeast of the Catalina at midafternoon. Safford had a heavy rainshower, gusts to 45 mph and a cool moist outflow a bit after 4 pm. This evening, right around Tucson, we're seeing mostly cumulus pancakeus, which fits the sounding shown above for 00 UTC - a tiny bit of CAPE right around 500 mb. Sounding is too dry by a bit more than 6 mm (compared to GPS PW) and the boundary layer probably has a well-mixed mixing ratio of about 4.5 g/kg. We'll see what morning brings!

Current Conditions

The current synoptic situation is fairly complex as a mid-level trof over California interacts with a weak lobe of the eastern anticyclone that is broken off over northern New Mexico. At higher levels, an unusually strong trough continues over most of the western US.

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Top graphic is this morning's (7 Jul 2010) Tucson (TWC) sounding. The sounding's PW and GPS PW are quite close and indicate PW of about 20 mm (values over much of Arizona are in the range of 20 to 25 mm this morning). The sounding is fairly similar to soundings about a week ago. There is cool air aloft from 500 to around 400 mb, above a very deep residual boundary layer, providing a layer with CAPE from around 600 mb to 400 mb, with warm air above in the upper-troposphere. Thus, a good sounding for high-based convection and possible dry downbursts. CAPE will be better over high elevations, but it is not obvious whether it will be large enough to overcome the very warm air aloft around 300 mb. It does appear that the southern Arizona boundary layer will continue to moisten gradually, via evaporation of virga and precipitation, coupled with moist outflows from convective storms over higher terrain.

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This morning's NAM 500 mb analysis (middle panel) indicates the trough over California and the wind field indicates the small anticyclone over northern New Mexico. These two features are interacting to produce the southerly, mid-level flow pattern. The model forecasts the California trough to retreat westward during the next couple of days as the larger, eastern anticyclone builds westward.

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The bottom panel shows the morning RUC analysis for 250 mb - quite a strong trough over the West and an ugly, strong westerly jetstream, off the Pacific, crossing southern California, Arizona and New Mexico.

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Last evening's operational GFS forecasts a nice precipitation event over southeastern Arizona for the 24-hours ending 5 pm on Sunday (11 July). The model forecasts amounts as high as a 1/4 to 1/2 an inch over lower elevations. The apparent driver for this forecast event is an inverted trough that the model forecasts (at 700 mb) be over the south Texas coast at 48 hours; just west of the Texas Big Bend Country at 96 hours; and much weakened but over southeast Arizona at 108 hours. So, we will have to watch how this feature materializes and advances during the next several days.

Taking A Look Around

Quite a bit of altocumulus and altocumulus castelanus around this morning (7 July 2010), and also last evening. Top image shows high-based convection, with snow virga, a bit before sunset last evening - photo taken looking south-southeast from the house. Middle view of puffy altocumulus taken by the Kitt Peak webcam looking north this morning. Bottom image is visible view from above - showing a distinct south-to-north band of cloudiness over Arizona. This is somewhat similar to the situation about a week ago.

Increasing Dewpoints

Pat Holbrook wrote: Monsoon start still looks on schedule for this weekend. Strong 250 mb westerlies aloft recedes as ridge builds in, only question is how fast the moisture will return I will be watching GYM next few days for a surge signal.
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There were actually a few cumulus around southeast Arizona yesterday afternoon and the trend should be for increasing moisture and cloudiness as the week progresses. The flow regime is quite chopped up in lower and middle levels over the Southwest and much of Mexico, so changes will be mostly associated with the westward building of the middle-level anticyclone later in the week.

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The graphics shown above are from the Tucson NWS monsoon pages - top graphic shows Tucson Td time series to date for this summer; middle graphic shows summer 2003; and lower graphic shows summer 2002. The onset of higher moisture (as indicated by the surface dewpoints) is often either very gradual (2003) or very sudden and implusive (2002). The sudden increase in 2002 was associated with the approach of a pronounced upper-level cyclone/inverted trough from the east. This feature moved across northern Mexico and southern Arizona triggering a northward push of subtropical air into southern Arizona. The top graphic seems to indicate that we're experiencing a gradual onset of higher moisture content in the low-levels this year. Some years do exhibit a mixed mode, and so the events of the next week or so will be interesting to observe.

Rains in New Mexico

Mike Hardiman reports from New Mexico:

Alex's remnants have resulted in some very impressive rainfall totals over a fairly small area around Del Rio, TX the past several days. One river gage site in Val Verde County reported 9.75 inches of rain Since July 2nd. PW at DRT peaked out at 2.60 inches yesterday morning with several RAOBs showing deep upslope flow with little upper level shear.

http://w1.spc.woc.noaa.gov/exper/soundings/10070412_OBS/DRT.gif

I would imagine that given the low level SE flow, even higher rainfall amounts occurred over the high terrain in Coahuila west of Del Rio.

Another Clear and Hot Day On Tap

Yesterday was deathly clear and was the second day with no precipitation reported in southeast Arizona; today will be the third with very dry conditions prevailing. This morning's 500 mb analysis from Univ. of Wyoming indicates dry, northwesterly flow from the Pacific over most of the western US and northwestern Mexico. The bottom image shows the GPS PW (and the TWC raob PW) for the past 30 days - from the GPS group at NOAA/Boulder. The observed PW has only flirted briefly with the important 3 cm threshold that some use to define the onset of monsoon conditions. Certainly a dismal start so far to the summer. Although Alex looked promising for a while, the storm's remnants stalled out over central Mexico, eventually pulling north-northeastward into the Plains. The NAM had predicted, at least for a while, that the 700 mb circulation with Alex would continue westward out over the lower GoC, but those forecasts did not verify. At this time, I don't see any feature in the model forecasts out to 6 or 7 days that would provide an impulsive northward push to the subtropical moisture - which at this time is quite far to the south down the GoC. There is quite a bit of activity in the Atlantic, Caribbean, and Gulf of Mexico to keep an eye on later in the week. After 3 or 4 days the mid-level, subtropical high build back westward across the Southwest and by 6 or 7 days conditions appear favorable for MCSs in Sonora to move into GoC during the nights. But that's about it - appears that we may have a very gradual development of the summer storm season here in southern Arizona.

Spitting Rain

Here is a replay of the spitting rain definition from two years ago - seem to be enough new readers that it's worth repeating this - storm in the video was exactly two years ago today!
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Saturday, July 05, 2008

Spitting Rain

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

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

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

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

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

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

Diurnal Td Surges at Yuma

An earlier post showed that WRF was forecasting a push of low-level moisture up the Gulf of California for yesterday morning. That did indeed happen - Td at Yuma yesterday morning at 6 am was 23F and at 8 am it was 69F. However, the low-level moisture quickly mixed out after a couple of hours. This morning at 6 am Yuma's dewpoint was again 69F, with strong southerly winds - see top image which is VAD wind profile from the NWS radar at Yuma. The low-level, southerly winds reach up to 2,000 to 3,000 ft. The satellite PW product (lower image) indicates that PW values are higher up the Gulf and into the deserts of southwest and south central AZ. With very dry air aloft, the higher dewpoints will mix out dramatically during the day. This is a typical diurnal cycle that we often see this time of year - daily late night/early morning sloshes of high dewpoint air north from the Gulf. This process helps gradually raise low-level moisture, but is much different than the impulsive Gulf surges that can bring large, and much deeper changes, within the course of a few hours.

Summary For July 2nd

Shower and thunderstorm activity was considerably diminished yesterday relative to the 1st of July. I can find the following for rainfall during past 24-hours: 5 of 97 Pima County ALERT gauges; 4 of 12 RAWS stations in southeastern Arizona; Douglas had 0.18" and Nogales had 0.01". Most measured rain was at high elevations and the greates amount I could find was 0.28" at Empire Peak, and all other amounts were less than 0.25", most considerable less.
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The PW time series for TWC (bottom) indicates a rapid drop in PW, after PW amounts had briefly reached 30 mm. The view of the Catalinas shows a continued dirty boundary layer at 7 am, but this will quickly mix out and we'll continue dry at low elevations and the only high elevation activity today (3 July) will be off to the east and southeast. So, Alex proved to be mostly just a tease for Arizona, although parts of New Mexico have fared very well the last several days!
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I can't help but remark on the following from today's early am FD for Tucson:
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A SIGNIFICANT INTERRUPTION TO THE MONSOON EXPECTED THE
NEXT FEW DAYS AS THE DRIER WESTERLIES WIN THE BATTLE AND PUSH
MOISTURE TO THE EAST OF SOUTHEAST ARIZONA.
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Most of us in southeastern Arizona who live and work at lower elevations have yet to experience a start of the summer storms as of yet. Here at house I have not observed lightning or thunder and last measurable rain was way back on April 23rd. We did have Traces on June 28th and July 1st but these were just pathetic spits of rain. Art Douglas has been away in South America and so we don't know if rains have started in earnest down in Ash Canyon. Long-time monsoon forecaster, Pat Holbrook, wrote yesterday that he sees hope for the start of the monosoon here in the metro Tucson area around the 9th of July. Most of us are still looking forward to that first rain that's heavy enough to provide serious cool outflows and to make the desert smell like rain.

Pat Holbrook's Outlook

Pat Holbrook writes: Bob,
Starting to hone in on a monsoon start between the 7th and 10th of July...poor model performance so far this summer as every next week forecast shows the ridge building in...then it doesn't happen. Will go with the 9th.

Pat
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Graphic above is this morning's ECMWF four panel prog for 168-hours (Friday 9 July at 12 UTC). Certainly looks like the return of Alex!

Another Mixed-Bag Day

Today is another difficult day, with very moist air close but not quite getting into southern Arizona. There is a shallow GoC surge signal at Guaymas this morning, but with very dry air just above through a fairly deep layer. El Paso is very moist and cool and has been strongly affected by the Alex remnants; however, southeastern Arizona continues in between the Alex remnants and the significant western US 500 mb trough. This morning's TWC sounding (top image) is quite similar to yesterday's. Bit of CAPE right around 500 mb but warm air just above. Mountains will have fair amount of CAPE and most action will again be over higher elevations. It appears the steering winds for deep convection will actually be from the west today. The morning NAM forecast for 24-hour precipitation valid at 12 UTC tomorrow morning is shown in the lower image. It shows a little bullseye around Douglas but mostly light mountain rainfall. After 24 hours the 500 mb trough pushes everything east for rest of weekend - at least according to the models.

Brief Summary Yesterday 1 July 2010

Nice summer set yesterday - photo above looking west-northwest from backyard. Here at house there was little to report. Could see some showers on the mountains but didn't hear any thunder. There were a few spits of rain in the the afternoon giving us a trace, and a nice cool wind from the Rincons in the evening. The airport carried a brief thunderstorm and a trace of rain. Douglas had a real thunderstorm and got 0.29" of rain. Only two of the 12 RAWS stations in southeast Arizona had rain (0.02" and 0.03") but here in eastern Pima County 27 of the 93 ALERT gauges measured rainfall - these were nearly all higher elevation gauges - and Rincon Creek came in with 0.43". The rain distribution yesterday illustrates that the change in Zone definitions coming this fall will yield some challenges. The higher elevation zone yesterday had POPs of about 100% and the lower elevation zone had POPs of about 0%.

Convection and Isolated Storms Cover Most of State

Fairly anemic convection over most of the state again this afternoon. Perhaps there'll be some stronger developments by evening? Tucson airport just reported thunder and an outflow that cooled temperature into the upper 90s. Updrafts overhead here, with building towers and some spits of rain - so some hope.

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Mike Leuthold reports from Maine -

Wow, you guys are really suffering in AZ especially at night, I see, due to the increase in moisture and the really strange strong SE flow. We're in Maine now and temperatures have been running in the low 70's here on the coast for high temperatures-I'm afraid to come back to AZ.
I've been keeping tabs on the WRF runs and though I'd bring to your attention today's run that has forecast a surge by 48 hours or so [48 hour Td forecast in bottom image]. The WRF GFS is a little stronger, but, as you say, the battle continues as the WRF keeps the surge out of far western AZ. It looks like the 3rd will be the most interesting day so far.

Mike

Battle Continues

Summary of yesterday - convection and a few thunderstorms again yesterday afternoon and evening. Limited CAPE and light winds kept most significant radar echoes at higher elevations. Nogales and Douglas recorded lightning from their single sensor systems and this may have been in-cloud signals? Closest CG strike I saw on the lightning maps was off near Benson, with most strikes over higher terrain far to the north and northeast. One station in Catalinas reported 0.04" and Keystone Peak (about 10 miles west of Green Valley) recorded 0.20". Only two RAWS stations reported rainfall - 0.04" at Columbine but an amazing 0.98" at Guthrie (if reading is correct). Guthrie is very near the New Mexico border where moisture amounts have been higher.

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This morning - downslope flow continues and the low was only 85F. Moisture has continued to increase slowly. The morning sounding and GPS PW values are very close and TWC PW has crept just over 30 mm - which some use as a threshold to indicate that moisture has reached levels associated with the monsoon. CAPE this morning appears quite similar to yesterday's, as moisture increases are offset by warming in upper-troposphere. A narrow tongue of cooler 500 mb air extends southward over eastern Arizona with ominous warmer temepratures of 4 to 6C both to west and east. Tropospheric winds remain very light.

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I've shown this morning's NAM forecasts for 06 UTC tonight in the three panels above. The models continue to indicate that the western US trough at 500 mb will dominate during the next several days and keep the subtropic flow regime suppressed to the south of Arizona. Thus, the key as to whether there will be a significant increase in low-level moisture for Fourth of July weekend will be over the southern half of GoC. If remnants of Alex can trigger significant convection on and west of the Sierra Madre Occidental, then a low-level surge may result. If, not then Pat Holbrook's assessment of too much troughiness in the west will prevail.

Westerlies and Subtropics Do Battle Next Several Days

Complicated situation continues. Yesterday there were storms and convection around southeast Arizona. NWS Tucson radar finally back in operation between 6 and 7 pm last evening. Thunderstorms/showers with strong winds at Douglas, Ft, Huachuca, and Nogales yesterday afternoon. Measurable rain at 5 RAWS stations in southeast Arizona, but max amount only 0.15" at Rucker.

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This morning the downslope flow continues, but moisture has gradually inched upward with values around 1 inch across the lower elevations. The TWC morning sounding data only a bit dry but with CAPE indicated very similar to yesterday morning. The NAM forecast runs this morning (12 UTC 30 Jun 2010) show the Pacific trough and the remnants of Hurricane Alex doing battle with southern Arizona sitting right in the middle of the two features. Right now the NAM seems to indicate the trough dominating.

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The images above show: the morning sounding at Guaymas (top) to be quite dry with less than an inch PW; the sounding at Mazatlan (middle) which is quite moist with PW well over 2 inches; the current NAM 700 mb forecast for 12 UTC Friday, July 2nd. I think that the remains of Alex moving into the lower GoC will have a good chance of triggering a moisture surge up the GoC. The cloudy and damp push at 700 mb, perhaps with areas of thunderstorms moving off the Sierra Madres, will bring dramatic cooling over the lower GoC. Such cooling at 700 mb, particularly with storms, often triggers a surge. So, what happens over the south half of GoC may well hold the key to local weather for the rest of the long weekend.

Morning Report From West Side of Tucson

John Diebolt reports: Another, windy and warm night west of the Tucson Mountains with moderate-strong easterly flow keping temperatures way up (89F at 5AM) TD up to 55 degrees by 5AM. With sunrise only a few meager clouds to the distant east..without vertical development. Have noted the airport has had rather stiff SE breeze betwen 10-15 MPH since 153AM but nothing like 24 hours ago. TD is nearly identical but temp is a few degrees warmer there. At the moment (5AM), RUC (from NWS TWC Monsoon tracker page) at 700MB showed TUS area in a bit of a Col with weak NW flow at 500 MB and 300MB with TUS at the northern end of the sharp 300MB trough from the TUS area southwest across central Baja. Sharp 300 MB northerly flow is shown advancing into western Arizona. Seems to agree well with very dry air seen on WV images in that area. Will be interesting to see what the 12Z TWC sounding shows us especially with the weak inversion above 500 MB..barring any bad data. Certainly not the ideal setup for a big day. Another round of mountain-huggers and gusty/dusty/hot in the valleys? (assuming the 500 MB subsidence inversion and dry air aloft does not supress things even more). Will be interesting to see what unfolds!