Sunday, October 23, 2016

WRF Models Forecast Thunderstorms This Afternoon

Although the thermodynamics are marginal, both WRF models from 06 UTC forecast afternoon thunderstorms over eastern Pima County today. The forecast of composite radar above is from the GFS variant and is valid at 2:00 pm MST today, while that below is from NAM version and is for 3:00 pm. Both models forecast small CAPE values of less than 500 J/Kg, but the situation is helped along by cold, middle-level temperatures (e.g., 500 mb temperatures of -10 C or less). The forecast skew T for TWC (at bottom) is from the WRF-NAM and is valid at 2:00 pm. The bulk of the CAPE occurs at temperatures colder than 0 C, and weak updrafts can produce considerable ice, lightning, and high reflectivity. The southerly winds at lower levels result in a slight increase in PW during the day, and high cloud bases could result in some gusty outflows.

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