Significant storms Yesterday

There was a definite increase in storm activity yesterday and several storms reached severe levels and/or dropped rains of an inch or more. The storms did not propagate into central Tucson and fizzled out much as forecast by the U of A WRF-GFS model.  Wind damage was reported in the northeast, where Mike Leuthold also reported gusts of about 60 mph. Power poles were down near the airport, and the Oro Valley area received heavy rains from the storms shown above at 3 pm MST. These moved west off the Catalinas into the Oro Valley area. There was measurable rain at 35 of the 93 ALERT stations in eastern Pima County (about 40% areal coverage), but only 3 of 20 sites in the Greater Tucson section of the network reported light rain. Here at house we were stymied again, observing only rumbles of thunder, several weak outflows, and a few sprinkles (Trace).

The above graphic is total rainfall (through midnight last night) predicted by yesterday's WRF-GFS midnight run. This forecast was far superior to the NWS NAM model, which has resolution that is far too crude to deal with the small scale forcing and ouflows that are predominating in this weak-wind synoptic setting. While the WRF details have hits and misses, the overall pattern of convection was nicely predicted.

This morning's Tucson sounding is shown above. Note that PW values are now very high (~1.75 inches) across the eastern 2/3rds of southern Arizona. Temperatures are warm in midde levels and as a result CAPE appears down a bit. The sounding PW has been very close to the GPS values for the last three soundings, and tended a tad wetter than GPS. There is a bit of light easterly steering flow from 500 to 600 mb and upper-level winds are from the west - so a bit of favorable shear (the NAM forecast seems to increase this a bit by evening). So, a continuing threat of wet downbursts and heavy rains where storms occur. The biggest unknown for today is how persistent a large area of debris cloud will be - currently much of south-central Arizona is clouded over, excepting Cochise County. So, the degree of local heating is questionable. The NAM forecasts continue to have only light precipitation along the southeastern Borderlands (similar to yesterday's forecast) for the next three afternoons. The early WRF-GFS forecasts a significant downturn in storms today - however, it appeared to me to have had intialization problems - so it would be wise to take a look at the 1200 UTC WRF runs.