Wednesday, July 11, 2012
Significant Increase In Thunderstorm Activity Today
This morning at 7 am MST (visible satellite image above and surface plot below) the heaviest cloud cover is over the GoC. Dewpoints have increased over the entire state and are in the 60s across the southern third of Arizona. An issue today will be how much heating occurs when and where - note, however, that the low deserts are starting out with very warm morning temperatures.
The TUS sounding at 12 UTC this morning (above) is quite moist, with a significant increase in CAPE present when compared to recent days. There are excellent east-northeast steering winds in middle levels and a good shear profile from middle to upper levels that will leave anvils trailing behind storms. The temperatures at 500 mb are -7 to -8C over Arizona (although there is warm advection possible over the southeast part of state). Soundings at the other three Arizona sounding sites are also impressive (Phoenix quite so!). Low-level easterly winds are stronger than I'd like to see. But all-in-all it looks like an excellent day for heavy (possibly severe) thunderstorms with a nice degree of mesoscale organization.
The early WRF-GFS forecast of CAPE at 2 pm MST this afternoon (above) has large areas of moderate CAPE forecast over much of the state. The composite radar forecast for 4 pm MST (below) has organized activity along the border, reaching northward into eastern Pima County (a weak inverted trough is brushing the borderlands today). In the western reaches of the Rim Country the model forecasts an organized MCS to move rapidly southward toward the low deserts east of the Colorado River. When systems like this occur, they frequently produce severe wind gusts. The forecast - a most interesting day on tap with a possibility for the most thunderstorm activity across the state of this summer.
Posted by Bob Maddox at 7:57 AM