A Showery Morning

What a pleasant change – cool, light showers, and heavy clouds (see 7:20 am KEMX radar chart). The subtropical system from Mexico did arrive a bit more quickly than the models indicated and easterly winds in mid-levels increased substantially during the afternoon. Thunderstorms developed on the mountains and moved into Tucson around 5:30 pm with gusts to near 50 mph and blowing dust. CAPE was apparently limited and neither TUS nor DMA carried a thunderstorm. A cell over the west flanks of the Catalinas developed after the first push and produced two rumbles of thunder here at house. I saw one CG strike to the north in the foothills. I should have paid more attention to my admonition on Tuesday that events such as this often develop more quickly than the models indicate.

Almost all observing stations in a large area of southeast and south-central Arizona had measurable rainfall, although amounts were generally light. In the ALERT network in Pima County only 8 stations did not measure rain. Five of the stations had 0.50” or more and Arivaca measured 0.94” – most amounts were around a quarter of an inch. The same is generally true for the Phoenix metro area ALERT network also (with the storms and rains arriving during the night and early morning hours this is the first significant rain event of the summer up there) with almost all stations having rainfall except for a few on the eastern edge. The rain amounts appear to have been heavier in the Phoenix network. Luke AFB had thunderstorms, gusts to 69 mph, and also the most rain reported at 1.00”.

There is substantial CAPE present in the TWC sounding this morning but obviously heating will be limited. A strong outflow from the mountains would likely produce spectacular storms with winds and R+ given the sounding – we’ll have to watch to see how the details evolve. There does appear to be instability for parcels lifted from elevated layers, so the forcing with the subtropical low, coupled with that of the mountains, should keep showers going off and on through evening. The low is being picked up by an upper S/W coming across the Southwest before the larger trough to the northwest affects us, drying things out again for several days. Abbreviated message – I have to get into Atmo for the daily discussion.