We're having more thunderstorms and rainbows here in nirth side of City of Tucson this summer than we are rain. Above is a diffuse, partial rainbow produced by muted sunlight reflecting off anvil clud to west. Strong thunderstorm cores stayed just to south-southwest and northwest of here yesterday, giving us a brief period of moderate rain that left 0.12" in the gauge. Much heavier amounts occurred near downtown, where there were flood warnings during the late afternoon. Was an unusual day in that storms avoided the high mountains and stay at mid-to-lower elevations, as shown on CG flah location plot below (for 24-hours ending at 11:00 pm MST, from Vaisala and Atmo). Although there were distinct southerly steering winds yesterday, many storms actually shifted southward (and other directions) from propagation due to new cell growth on the flanks of many storms. Only 26 sites within the ALERT network received rainfall yesterday, but several sites near the airport were near or just over an inch. There were a couple of wind damage reports near the airport also - as well as gust to 67 mph out at Pioneer Airfield.
We are beginning another dry-down and today is the transition day. The CIRA blended PW analysis for 12 UTC (above) shows that PW remains high to the west of Tucson and the morning sounding (12z skewT below from SPC) indicates some CAPE and westerly wind below 500 mb. So the drying will not become pronounced until subsidence eats away at the moisture to the west. The 06 UTC WRF-NAM forecast drops PW rapidly after 1:00 pm this afternoon, while the GFS version holds onto some higher PW and CAPE through the early evening. So, the NAM version keeps all storm activity to south and east of Tucson metro, while GFS version brings several storms across parts of eastern Pima County during the afternoon. The graphic at bottom shows 06 UTC WRF-NAM total rainfall forecast through 11:00 am MST on Wednesday the 5th - not much on the horizon acording to this model forecast.
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