Thursday, July 15, 2010

Interesting Couple Of Days On Tap For Southwest And Southern California

Yesterday – another mostly down day with some mountain storms and some anvil sprinkles over the Tucson metro area. The airport and DM each had 0.01”, while much of the rest of area had traces, as per here at house. No thunder observed here or at the air terminals. The ALERT network had rain at 11 of 93 stations, again mostly light – except a lunch hour heavy shower up on the Catalinas produced 1.02” at the Mt. Lemmon ALERT gauge. Only 3 eastern RAWS stations had light rain. The TWC soundings the last two evenings have had thermodynamic profiles that might have supported low-elevation storm, had there been strong outflows from the east – but done in by the L/V winds in much of troposphere.

Today – PW remains moderately high at low elevation stations (42 to 45 mm) but winds in lower 2/3rds troposphere remain light. The remnants of yesterday’s upper-level inverted trough appear to out over northern Baja, extending into southwest Arizona (see WV image at top). Note also that the inverted trough/cyclone that has been stuck over the Pacific west-southwest of San Francisco still persists (I don’t know if this strange feature has somehow affected what’s been happening over the Southwest – any thoughts?). The morning soundings at TWC (middle image) and PHX have been modified by old cloudiness from the MCS that remained mostly inland over Sonora during the early morning hours – they are “onion” soundings and hard to evaluate for this afternoon. It is of note that the San Diego sounding is quite moist and has CAPE aloft over the marine layer – it looks like the best storms today may be over there in southern California. The NAM also forecasts some late evening activity along the Arizona borderlands, where there appears to be some upper-level difluence. Mountain forced storms could drift over random locales, and the NAM continues to forecast that mid-level steering flow will strengthen from the east.

Tomorrow – The NAM model continues to indicate an improved situation late afternoon and evening for southeastern Arizona – see the 500 mb forecast valid at midnight Friday night in bottom image. Note that as the 500 mb anticyclone reconfigures itself, it appears that some cooler air could be advected around the eastern side – from northern Utah and northwestern Colorado into southeastern Arizona.

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