A Meteorological Potpourri

Another afternoon of anvil overcast and various amounts of both towering Cu and debris clouds yesterday afternoon. Net result was that there was limited storm and rain coverage once again. Most intense storms appeared to be off to the east, especially around Benson and Sierra Vista. Not even a spit here at house. At 5 pm yesterday only 12 of the ALERT gauges had recorded rainfall during the past 6 hours (about 13% areal coverage). Only one more site had picked up rain during the night - so nighttime rain has been essentially absent in eastern Pima county the last couple of nights. The actual POPs have been well below climo, even though moisture has been very high. So it goes, with such a chopped up synoptic setting.

Satellite IR image from 1430 UTC indicates a large and intense MCS along the middle and lower GoC.
---------------------------------------
Hurricane Greg is apparently going to track westward and stay south of 20 degrees N for most of its life - too far south to have impacts this far north.
----------------------------------------
Sounding this morning is similar to last several mornings - decent CAPE, PW over 40 mm, winds very light below 300 mb, and strong southerlies at anvil level. Thus, mountain storms again likely to throw out copious anvil clouds as per yesterday. The 500 mb anticyclone by evening forecast to be nearly overhead, with upper-level winds becoming more southwesterly.

The NAM 1200 UTC forecast and the GFS-WRF early run forecast of rainfall through midnight tonight are shown above. The NAM again is very agressive with QPF for southeast Arizona - note the heavy maxima near Nogales and the Santa Rita Mountains. The WRF-GFS however forecasts most activity and heavy rains in a north-south band in Cochise County - extending just into the Catalinas and Rincons. So the models are quite different in their details, although both forecast much more storm activity than has occurred the last two days. I did note that the WRF-GFS appeared to have forecast too much early morning convection and cloud in northeastern Sonora - so that may be impacting the afternoon/evening forecast. 

Finally - the above is the WRF-GFS forecast sounding for TUS valid at 5 pm MST this afternoon (i.e., at 0000 UTC 19 August). Note the two very different saturated layers between 700 and 500 mb - the lower layer is easy to understand as updraft air, but I can not come up with a good physical explanation for the cold, saturated layer below 500 mb - thoughts anyone?