Pacific Troughs Overhead

It is a cool and humid morning here, and I've gotten off to a late start - so a brief overview of yesterday and a summary of the situation today. Top photo is from John Diebold and is of a building storm north of the Catalinas yesterday at about noontime.

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The Tucson metro area was mostly surrounded by large storms yesterday - northwest to south to northeast. A stable outflow moved through the local area a bit after noon, and there was a brief shower here at noon that left 0.01", and that was it for the day, other than anvils. Only 22 of the 93 ALERT gauges had rainfall during past 24-hours (about 25% coverage) and only 4 of these were half an inch or more. White Tail had 1.26" and Anamax way down south had 2.20" to be far and away the heaviest amount I found this morning. Four regular reporting stations had very light amounts under a tenth of an inch. However eight of the higher elevation RAWS gauges had rain - again light amounts except for 0.48" at Sasabe and 1.39" at Carr. Frank fizzled out rapidly yesterday afternoon and became a weak depression that probably won't have much impact, since it will be kept to south by the Pacific troughs now affecting the Southwest.

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John Diebold sent a couple of messages late yesterday about his expectations for today - ...moist air over us will be pushed up against the higher terrain to our immediate northeast and lead to an active day over Gila/Graham/Greenlee and Cochise counties and possibly parts of Santa Cruz
county as storms fire as close as the Rincons/Catalinas. There may be a few isolated towers going up near the high terrain of south central Pima and into adjacent north central Sonora... and I tend to agree.

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Most of the western US is now completely under the influence of two Pacific troughs, as nicely indicated (for upper troposphere) in the middle water vapor image. The heights at 500 mb this morning, bottom chart - especially if additional contours are added - show that Arizona is completely within the circulation of the two troughs, as do the height contours all the way down to 850 mb.

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The morning Tucson sounding has small CAPE and westerly flow at all levels except for very near the surface. PWs across southern Arizona are low to upper 30 mms and the trend through the weekend will likely be down. Dewpoints remain high at Yuma and there may be some storms over higher terrain of southwest and south-central Arizona, but most significant storms will likely be over the higher terrain of the east half of the state. So it's a transitional situation today with lingering moisture and relatively strong westerly shear aloft - good setting for some strong storms but less so at low elevations. Interestingly, this morning's NAM forecast shows a local center of heavy precip falling by midnight north and east of Tucson - assume this reflects higher elevation storms. Will be interesting to see the U of A WRF forecasts later this morning.

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Corfidi at the SPC notes in the latest severe outlook: ....SWLY MID/UPR LVL FLOW WILL BE SUFFICIENT TO SUPPORT A FEW SUSTAINED STORMS/POSSIBLE SUPERCELLS GIVEN SUFFICIENT LOW LVL CONVERGENCE TO PRODUCE STRONG UPDRAFTS. ATTM BELIEVE THIS THREAT WILL BE GREATEST OVER CNTRL/NRN PARTS OF THE STATE LATE THIS AFTN AND EVE...ALONG AND N OF THE RIM.

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Remains to be seen how much of a monsoon killer this trough will be - the models tend to bounce the 500 mb anticyclone back to west quickly - the ECMWF is the most dismal of the longer range progs tending to keep ridge axis along or south of border.