Some Heavy Storms Yesterday

Mountain storms occurred a bit further to the west yesterday and produced some rain over the high-elevation stations across the eastern part of the Pima County ALERT network (24-hour coverage - 18 of 92 stations). Graphic below shows lightning strikes detected for past 24-hours ending at 6 am MST this morning. Most of the storms were again off to the east, but note that were CGs in the Catalinas, Rincons and along a swath that started in the Santa Ritas and ran off toward Benson. The White Tail site along the Catalina Highway caught a local downpour and reported a total of 2.16" - just over 2 inches of this fell in less than an hour. Nothing again at low elevations and not even a sprinkle here at house for 7 days now. There was a strong outflow from the east across parts of town around 4 to 5 pm during the afternoon.

The morning run of the WRF-GFS indicates Pacific flow dominating, with CAPE vanishing by early afternoon across most of southeastern Arizona. Precipitable water amounts have fallen below an inch at all the southern Arizona sites except for the southeastern corner. The model forecasts bring the PW back up over an inch during the day on Wednesday, as some moisture returns from the south.

Water vapor image from 6 am MST (above) shows very dry upper-tropospheric air over Arizona and southern California. An inverted trough in the lower troposphere along the west coast of Mexico has resulted in early morning storms over the southern portions of the GoC. Lightning strike data from Mexico for 12-hours ending at 6 am this morning (below) show a high strike-density across the mouth of the Gulf.

The current time series of GPS PW from the Atmo page, above, show the dryness over southwestern Arizona that extends down the GoC past Hermosillo, which still has PW less than inch. At 8 am MST this morning Hermosillo reported a temperature of 88F with a dewpoint of 36F - ugh! The Hermosillo time series of PW will be a good indicator of when low-level moisture returns up the GoC. Meanwhile hot and dry conditions prevail.

Some Storms On Mountains

We were away Friday afternoon and yesterday at Santa Rita Abbey (~ 5 miles NW of Sonoita). The Sisters measured 5.28 inches of rain during July, and the landscape has certainly responded with greenness rivaling Wisconsin in summer (above was taken early yesterday morning - Saturday August 10th). When we drove back around 5 pm yesterday there were mostly high-based flat cu around with some storms visible far to southeast to northeast. The plot of 24-hours of CGs ending at 6 am this morning (Sunday August 11th) shows activity in Cochise County, with most storm activity up in the White Mountains. Pima County ALERT network recorded no rainfall for 24-hours ending 6 am this morning - making 4 straight days of no rain and serious suppression.

The CIRA blended precipitable water product for 6 am (above) shows values of inch to an inch and and a quarter or so across southeast Arizona. Very moist mT air remains far to the south over the southern third of the GoC.

The early run of the WRF-GFS at Atmo today forecasts some storms across eastern Pima County. The skew-T forecast above is valid at 2 pm MST this afternoon. The sounding has a fair amount of CAPE, although considerable lifting would be needed to release it at low elevations. We are mostly in southerly flow below 500 mb and westerly flow from the Pacific above - a fairly dismal sounding for rain, but high-based storms and gusty winds possible. The instabilty is due to the cold (for this time of year) temperatures of around -10 C at 500 mb combined with very hot boundary layer with surface temps over 100 F. The model forecast of rainfall through midnight (below) shows mostly light amounts at low elevations of eastern Pima County and keeps most of the more significant storms off in Cochise County and the White Mountains again.

The model forecasts Pacific air to dominate here on Monday and Tuesday with activity shifted even further east.

Miscellany 9 August 2013

Another very pleasant morning for walking here in north Tucson. Temperature at house was around 65F at sunrise. My walk took an unusual turn when a three-legged, medium-size dog tried to attack me. He was amazingly fast, quite vicious, and the owner who was a long way away, didn't seem concerned. Had to fend him (the dog) off several times with my walking stick.

On to the weather, which won't be near as exciting. Yesterday was again totally suppressed. No lightning in Sonora, Mexico, and only some isolated strikes up in the northeast corner of Arizona.

The early WRF GFS forecasts from Atmo indicate a return of middle-level moisture from northern Mexico, with some high-based convection in southeast Arizona both tomorrow and Sunday. The forecast of composite radar echoes, (above) valid at 3 PM MST on the 11th (Sunday), indicates isolated showers in eastern Pima County. The PW forecast valid the same time (below) indicates amounts of water vapor in the troposphere nearly doubling by then, with amounts over an inch.

The Tucson skew-T forecast for 3 PM Sunday is shown above. Winds are southerly from 700 to 500 mb, where there is a sliver of CAPE. High-based showers and virga and gusty winds seem possible, but meaningful rainfall remains out somewhere on the far horizon.

Dry And Cool Morning

Nice clear view of Baboquivari to south of Kitt Peak, above at 7 am MST this morning. Very pleasant morning here after the dry out of yesterday. The extent of the suppression yesterday was very large, as shown by the lightning strike plot, below for 24-hours ending at 6 am this morning. All of the southern half of Arizona and most of Sonora, Mexico, had no thunderstorm activity.

Time series of GPS precipitable water at Univ. of Arizona site for past 14 days (above) shows PW has dropped to its lowest value in many days, with only 3/4 of an inch this morning. Hermosillo has less than inch also, and all the way down at La Paz the PW is just over an inch. Big question will be how long it will take for low-level, mT air to make a return into the Southwest. The graphic below (from the early WRF-GFS on the 5.4 km grid) shows forecast total rainfall through 8 pm MST Saturday evening. The only meaningful rain in this forecast over southeastern Arizona is indicated on some of the mountains - a quite dry forecast for this time of year. The eastern Pacific is becoming more active, however, so we can hope for some help from disturbances in the subtropics next week.

Dry Out Today - 7 August

Yesterday turned out fairly suppressed from the Tucson metro area northwestward (above graphic shows lightning strikes for 24-hours ending at 6 am this morning). The fly-in-the-ointment was a strong outflow that came in from the northwest between 9 and 10 am in the morning. This kept thunderstorm activity to the south and east of the metro area. We had a couple of sprinkles and a trace here at the house. Across the ALERT network 38 sites (41% coverage) reported rainfall that was mostly light. However, Florida Canyon under that swath of CGs across the corner of Pima County, reported 1.10" and Bellota Ranch on Redington Pass had 0.91".

This morning the Tucson and Phoenix soundings remain unstable. There is a patch of higher PW persisting over south-central Arizona with values near 1 1/2 inches - the light-bright green area on the CIRA blended PW product above from 6 am MST. The 500 mb trough has moved off to the northwest this morning and west to northwest winds are advecting much drier Pacific air into southern Arizona and northern Mexico. The early WRF-GFS forecast below of PW valid at midnight tonight tonight illustrates the dramatic dry out that underway today. Things stay dry for a couple of days.

Storm Near Douglas Yesterday

Photographer Mike Oblinski caught this storm near Douglas, Arizona, yesterday afternoon (Monday August 5th). He has a description of his chase on his blog at:     http://www.mikeolbinski.com/theblog/2013/08/a-hail-core-near-douglas-arizona/

There is also a video at:    http://vimeo.com/71852487
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Interestingly, Douglas had another severe storm today at their airport which produced over 3/4" of rain and a gust to 64 mph right around 1 pm.

Cumulus Fractus Along Catalinas This Morning

Look At Early WRF GFS For August 6th

This morning there is south-to-north trough over central Arizona at 500 mb (12 UTC analysis above from NCAR RAL). This feature, which brought yesterdays rains to the Tucson area, is associated with a very large area of clouds and showers across all of Arizona except for the southeast corner - below is visible image from 7:15 am MST.

This morning's 12 UTC TUS sounding above shows several things of interest. The winds are southerly to southwesterly through most of the the troposphere; precipitable water remains high; CAPE is higher than it was yesterday; and there is a rain-cooled layer below 850 mb. Main question will be whether sunshine and heating will be enough to allow the boundary layer to recover this afternoon.

The early run of the WRF GFS indicates that storms will occur again this afternoon over eastern Pima County. The forecast of composite radar echoes, above valid at 5 pm MST this afternoon, indicates a large storm area southwest of metro Tucson. Steering-level winds become southwesterly this afternoon and the model forecasts considerable rainfall by 6 am MST tomorrow morning - below. I've clipped the forecast of accumulated rain to avoid the ongoing morning precipitation to our west and northwest - thus forecast below is of rainfall forecast this afternoon and evening.

Brief Summary Of August 5th

Yesterday afternoon and evening thunderstorms stayed mostly on the higher elevations, although widespread storm debris produced light showers over most of the lower elevation areas. The result was the coolest and most humid morning of the past seven days, as shown by the time series for TUS above. A plot of lightning strikes for the 24-hours ending at 5 am MST this morning (Tuesday August 6th) below, indicates activity mostly on the higher elevations with isolated, random strikes over eastern Pima County. Rain occurred at 87 of the 92 ALERT sites during the 24-hours ending at 5 am MST - apparently (unless I've missed a day) the most widespread rainfall event so far this summer.

I've snipped two segments of the ALERT network - the Rincons and east metro above, with the west metro and Tucson Mountains sector below. These graphics illustrate heavier rains over the Rincons, and heavier amounts also fell over higher elevations of the southern sector of the network. Here at the house there was lightning visible, mostly to the east and southeast after dark, but we only received 0.09" in light showers. Rains here at sunrise yesterday amounted to an additional 0.03".

Finally, Tropical Storm Henriette has become a hurricane and is heading off to the west, as did Flossie and Gil - this morning's NHC forecast is below. Henriette may brush the Big Island, as did Flossie.

Morning Storms Again - 5 August 2013

It was again suppressed in the Tucson metro area yesterday afternoon. Above radar is at 5:20 pm MST yesterday, showing only some lingering debris echoes. However, the early WRF-GFS yesterday forecast activity again after midnight and it was fairly accurate. Below is 5:00 am TUS radar composite chart this morning. An outflow from a decaying MCS, which originated in northern Mexico west of the Big Bend, moved westward across the Tucson area around 4:30 to 5:00 am. The gust front was accompanied by light rain but little or no lightning. Here at the house we managed only a couple of hundreths.

Little rain again across the ALERT network. At 5:00 am MST this morning only 6 sites had reported rainfall during the past 6-hours and 11 sites had rain during past 24-hours. An isolated cell produced 1.69" down at Florida Canyon. At 3:35 am this morning Douglas reported a gust to 47 mph from the east and rainfall there was 0.88".

An IR image from 4:30 am is shown above. The early WRF GFS forecast run at midnight at Atmo did reasonably well, predicting the early morning MCS. Below is the model forecast of composite radar echoes valid at 5:00 am MST this morning. The early WRF-NAM and also the NAM forecasts from midnight forecast no morning storms in most of southeast Arizona. The early morning event throws a monkey wrench into the works for the rest of the day and we'll have to observe how things evolve.

Some Sunrise Storms - 4 August 2013

Yesterday was very suppressed in the general Tucson area, with afternoon storms out to the west in central Pima County. Nothing here and 0% coverage across the ALERT network at 6 pm. But early morning storms have brought some rain to the eastern part of the network - 11 stations (12% coverage) have reported rain in the last 24-hours (Manning Camp in the Rincons had 0.39"). First thing I saw when I got up early was a lightning flash off to the east-northeast.

Several MCSs in west and north Mexico during the night, with outflow from one that dissipated south of Cochise County apparently kicked off the early storms - mostly east and south of the metro area. The composite radar chart from the TUS Doppler is from 6 am MST.

The morning storms will cause problems during the day, making the forecast quite difficult. I have looked at Amo's early runs of both the WRF GFS and WRF NAM. The two forecasts are very different. The WRF NAM (not shown) forecast no early storms or rain, so it has immediate problems. It does forecast mid-to-late afternoon storms mostly to the south and then, interestingly, forecasts another round of storms tonight after midnight. The WRF-GFS forecast development of the early storms (above is forecast composite radar valid at 7 am MST); however, the location and extent of the storms seems off. The GFS also forecasts a very significant outflow from these storms (10-m winds valid at 7 am shown below). This outflow serves to stabilize things over eastern Pima County, so that afternoon storms are suppressed in the forecast.

Above is the WRF GFS forecast of rainfall through noon today and it shows that the heavy rains to the southwest of Tucson generated the large mesohigh and strong outflows. The GFS version of the forecast does not forecast storms after midnight, except down in Mexico. So too very different model outlooks for the next 24-hours. The 7 am radar data indicate new storms developing southwest of Tucson and also over Cochise County - so the GFS definitely has a better forecast for the morning.

The 12 UTC skew-T plot for the TUS upper-air sounding is shown below. More moisture present this morning, as well as some elevated CAPE. Steering winds are from the south at 10 to 15 kts, with fairly strong winds in the upper-troposphere. So another day where the forecast is not obvious, except for its complexity.

Drier More Stable Air Mass This Morning

Storms tended to keep to higher elevations yesterday - CGs for 24-hours ending at 5 am MST this morning show a relative minimum centered over Tucson. Across the ALERT network only 20 sites had rainfall, but there were 8 sites with more than half an inch and 3 with more than an inch (max 1.43" at Mt. Lemmon). Here at the house a storm developed nearly overhead and produced 0.17" of rain at mid-afternoon yesterday - and that light amount is, sadly, the most rain for any day this summer here.

The TUS morning sounding plot (above) shows a considerable decrease in PW (34 mm down from more than 45 mm yesterday) with an attendant decrease in CAPE. The time series of GPS PW (below) shows this intrusion of drier air - which has pushed across southwestern Arizona on low-level westerly winds.

The early WRF NAM run at Atmo forecasts a battle between dry and moist air today, centered over central Pima County. The forecast of 850 mb dewpoints is shown above for 5 pm MST this afternoon. But the forecast of composite radar echoes valid at 6 pm (below) indicates a small cluster of storms centered right over Tucson. So the model keeps enough moisture for storms here in eastern Pima County, but westerly winds could prevail and keep things relatively suppressed - will be interesting to see which air mass prevails. Cloud bases will be considerably higher than last several days and the model forecasts a strong gust front across metro Tucson with the storms.

Finally, a very large early morning MCS affected much of central US after midnight - water vapor image below is from 1315 UTC - couldn't resist showing this!.

Strange Day Yesterday

It was a strange day yesterday, with cloud cover hanging around most of the day. Thunderstorms developed by 11 am and intensified over Cochise County (above is regional radar from NCAR RAL at 11 am MST on the 1st). The storms to the east produced a fairly strong outflow that moved across the Tucson area around 1 pm. So, the low-levels were stabilized for most of area, although a couple of strong storms developed in the afternoon to the east and south. The ALERT network had only 9 stations with precipitation through 6 pm - Haystack Mountain on the far southeastern edge of the network reported 0.93". Here at the house a light shower around 1 pm left 0.09" in the gauge. By 8 pm MST (see WV image below) last evening activity continued down in Mexico, with abundant anvil cloud over southeastern Arizona.

Precipitable water has continued to creep upward over most of southern Arizona, due both to the outflow mentioned above and southerly from along the GoC. The Tucson morning sounding today (see skew-T plot above for 12 UTC) indicates 1.77" of PW, with a noticeable increase in low-levels. The sounding has increased CAPE at low elevations, relative to last several days. Winds, however, continue light and variable below 300 mb and a very weak trough is embedded within the larger anticyclone. This feature is over east Arizona at 500 mb. So, storms that form today may be more widespread and certainly have the potential to produce heavy rains and perhaps wet microbursts.

There are internet problems at Univ. of Arizona this morning and I can't reach any sites over there. The morning NAM forecasts another strange with storms and rain, centered almost over Tucson, beginning this morning and continuing through about 3 pm. I can't say that I have much confidence in that forecast, but based on the strange happenings yesterday, I can't totally discount it either. Observations will eventually tell what the day will bring.

Overview August 1st

Not much time this morning. Note that Gil is now a Cat. 1 hurricane. Some precipitation returned to high elevations of eastern Pima County yesterday. Eight sites (9 %) in the ALERT network had rainfall through 6 pm yesterday afternoon - none after that. Rain was in the Catalinas and Rincons and all amounts were less than a tenth of an inch, except at Manning Camp which reported 0.43". Most lightning through evening yesterday (above) occurred in Cochise County. The Tucson sounding this morning (12 UTC skew-T below) is more moist than yesterday with 42 mm of PW. However low-level CAPE remains slight. Winds aloft below 300 mb are light and variable. So August starts out like much of July.

There is considerable cloudiness over the Southwest this morning and convection was still active at 14 UTC over the southern 2/3rds of the GoC. The convection, in conjunction with an upper-level low off southern Baja, will push low-level moisture back into southwestern Arizona today or tonight. Although situation is somewhat stagnant, the latest NAM forecasts a wet afternoon and evening for all of eastern Arizona (precipitation forecast through midnight tonight shown below). Crude NAM resolution results in some heavy mountain rains being smeared into lower elevations. Couldn't find any 06 UTC WRF forecasts this morning.