Wednesday, October 06, 2010

Some Serious Overforecasting of Thunderstorm Threat Today

Have been away all afternoon and have just taken a look at the afternoon data. It appears that serious over-forecasting of the thunderstorm threat for southeastern occurred, well into the afternoon, by the NWS. Perhaps this is not surprising given the apparent moderate-level outbreak in south-central Arizona yesterday and this morning's tornado swarm (as per NPR) near Flagstaff.
Top image shows the SPC diagnostic plot of the special 18 UTC sounding taken at Tucson. This sounding was a couple of mm too moist wrt GPS PW and, if one ignores the unrepresentative surface data, it has absolutely NO CAPE within the boundary layer - a serious decrease in storm potential from the morning sounding (see previous post). The hodograph is very nice, with substantial helicity (especially for down here!), but it needs some CAPE to do anything. However, the NWS forecast products continued to highlight a chance for storms with heavy rainfall and a chance for supercells and severe thunderstorms. The middle image shows the SPC severe thunderstorm outlook issued at 1938Z, after the special sounding.
Bottom image is the RAP regional radar composite at 2000 UTC this afternoon - this is as active as it ever was across southeast Arizona today - totally suppressed wrt deep convection.
The Univ. of Arizona, high-resolution, WRF models runs yesterday had indicated that today would be suppressed across southeast Arizona. The runs from this morning's data again repeated the forecast of no deep convection over southeast Arizona today. Mike Leuthold pointed this out in his morning WRF model forecast discussion, which proved to be right on!

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