Thursday, August 18, 2016
Quick Look At Today
During the late night and early morning hours there was considerable thunderstorm activity from western Pima County northward to regions well west of Phoenix - plot of detected CG flashes above from Atmo and Vaisala for 24-hours ending at 6:00 am MST this morning. These storms were well predicted by yesterday morning's WRF forecasts - see Mike Leuthold's early afternoon discussion at:
This morning low-level moisture has increased back to around 1.25 inches, as higher PW to the west has inched eastward. The blended PW analysis above is from CIRA at Colorado State University and is for 11 UTC. Driest air continues over far northwest and southeast Arizona.
This morning's skewT plot of the TWC sounding data (above from SPC) is somewhat similar to Tuesday morning's. The upper half of the troposphere remains in a westerly flow regime, with features of interest residing in the lower half, where the wind field remains weak and chopped up. There are three elevated mixed layers (EMLs) present from just above 500 mb down to just above the surface. The lowest of these has considerable CAPE, but the two old boundary layers above are hostile and stable, meaning that considerable forcing would be needed to produce storms in eastern Pima County.
The forecast of PW below is from the 06 UTC WRF-NAM and is valid at 5:00 pm this afternoon, when the model predicts a strong east-to-west moisture gradient across Pima County. The evolution of storms this afternoon will depend very much on where storms first develop and how their outflows evolve. My first guess, based mostly on the morning sounding, is that storms may be most likely in our area during the night and early morning hours. Best strategy is to check the 12 UTC WRF forecasts and watch for Mike's discussion later today.
Posted by Bob Maddox at 6:49 AM