Locally Severe Thunderstorms Yesterday

The 12 UTC run of the WRF-GFS at Atmo yesterday forecast much more storm activity than did the early run (06 UTC) - see previous two posts. The 12 UTC forecasts for the metro area verified reasonably well - above is 6:11 pm TUS composite radar. Strongest storms occurred mostly north of !-10 and at low elevations for a change. A storm at DM AFB produced 0.83" and gusts to 56 mph. Here at the house we had 0.76" and gusts of 55 to 60 mph around 6:20 pm MST. In contrast, TUS had a trace and Atmo measured 0.13". Across the ALERT network areal coverage was a bit more than 70% during the past 24-hours. There were 12 stations with more than half an inch. There were limbs down in the local area this morning - mostly small, but I saw a couple of larger limbs down when I walked this morning.

The afternoon Tucson sounding (skewT plot above from Univ. of WY upper-air site) was taken a bit more than hour before the severe thunderstorms developed - note that the sounding indicates almost no CAPE. However, the times series of GPS PW vs raob PW (below) indicates that the sounding was more than 2/10s of inch too dry. Thus, the apparent lack of CAPE was caused by bad data from the Sippican sonde in the boundary layer. As I reported earlier, the NWS is testing a replacement sonde because of numerous problems with the Sippican sonde. Also of note is the increase of PW through the day yesterday - probably due to moisture convergence in the old frontal zone that had eased into southeastern Arizona.