More Active Day Today?

Some storms around yesterday but activity mostly avoided central Tucson area. Strong cell shown above (northwest of Tucson near county line), in 2300 UTC composite radar from RAP, produced a wet downburst and over an inch of rain in less than an hour. Many power poles down and some people trapped in buildings for several hours because of live lines down. Here at house I could see several storms in distance - both southeast and northwest and on Catalinas (might have been thunder here, but I didn't hear it), but only a couple of very slight sprinkles - Trace day. I checked the ALERT network at 5 pm yesterday afternoon and 14 stations had had rain during past 6-hours (only about 15% areal coverage). This morning's data indicates no stations had rain after 5 pm yesterday - so, except for the one severe storm, a pretty quite day - much as predicted by the Atmo WRF-GFS.

Visible satellite image (above) at 1430 UTC this morning (Wednesday 17 August) shows mostly clear skies over most of southern Arizona - so another day with a lot of sunshine, which is a plus. Tucson reached 99F yesterday at the airport.

The Tucson sounding this morning (above) remains quite moist (actually a bit too moist wrt GPS data) and SPC diagnostics indicate considerable CAPE. Note however, that heating and mixing will result in a deeper BL and afternoon CAPE at low elevations will be about 50% of what's indicated above. Temperatures at 500 mb are quite warm, with no cooler midlevel air indictaed upstream. Winds have increased a bit - there is a leyer of southeast winds around 500 mb with speeds of 15 to 20 kts. Winds at anvil level are from about the same direction at around 25 kts - so anvil shading will again be a problem. Both the NAM and the early run of Atmo WRF-GFS forecast decreasing wind speeds in midlevels this afternoon, which would acerbate the anvil shading problem. But, both models also forecast a considerably more active day in the immediate Tucson area. One other cautionary note however - there does appear to be some drier air sneaking in from the south - see GPS PW time series for U of A below, indicating vales around 1.4" a couple of hours after the morning sounding. So a number of pros and cons in play today.