Thursday, August 25, 2011

Quick Look 25 August 2011

First, the early WRF-GFS for yesterday (earlier post below) actually was quite good, except for under-forecasting the convection in the middle San Pedro Valley and extreme eastern Pima County.

The 1530 visible image (above) shows that there is still quite a bit of debris cloud lingering over south-central Arizona. A big issue will be how much heating we get this afternoon - the storms yesterday produced some low-level cooling, but not enough to really cut down temperatures unless the clouds persist well into afternoon.

The morning Tucson sounding (above) has no CAPE indicated - thus, for low elevation storms we'll need to recover some boundary layer (BL) moisture - note that at least shallow moisture returned up the GoC to Yuma yesterday. The Guaymas sounding this morning has PW of over 65 mm - more than double what's over Tucson. At least a decent steering flow has finally developed in the 600 to 400 mb layer, where winds are essentially easterly at from 15 to 20 kts. The 500 mb anticyclone is broken into two lobes this morning - one over western Arizona and one over southeastern Colorado, with a weak trough/shear zone between from north of Guaymas northward into the Four Corners region. These features are nearly vertically stacked in the upper-troposphere this morning - but the NAM model forecasts the anticyclone to consolidate along the Colorado/New Mexico border during the next day or so.

The early Atmo run of the WRF-GFS bascially forecasts a repeat of yesterday for the Tucson area. Forecast above is a surface plot valid at 5 pm this afternoon. The model forecasts storms and several strong outflows to move into the metro area between 4 and 5 pm MST.

The model also forecasts an increase in precipitation across southeastern Arizona this afternoon and evening wrt yesterday. It forecasts substantial storms again in the central San Pedro Valley this afternoon - a possible model zig-zag?
The early WRF-GFS run today also indicates a completely down day tomorrow, as it forecasts a substantial intrusion of dry, low-level air from the east. So, several interesting things to keep an eye on out here in the Southwest.

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