Saturday, October 08, 2016

An Interesting Day For October

Interesting skies at sunrise with considerable iridescence over the Rincons. East winds of 20 to 30 mph and mild temperatures. The push of easterly flow has spread across much of southern Arizona this morning and as the winds become more southeasterly, models forecast PW to increase.

Winds did gust from 40 to 50 mph at the Mt. Hopkins RAWS site last evening from around 8 to 10 pm, as the backdoor front moved by.

This morning's TWC skewT plot is not very impressive, except for the 500 mb temperatures of around -12 C, associated with the weak short wave moving our way today. Moisture is lacking and there is only a sliver of CAPE indicated by the SPC analysis.

The CIRA blended PW analysis below is for 12 UTC and indicates that PW over our area is generally a bit less than an inch - light blue shades. Thus, low-level moisture convergence is probably needed to increase CAPE by the afternoon.

Shown above is the 06 UTC WRF-GFS forecast of the TWC sounding valid at 1:00 pm MST - quite a change with substantial CAPE (~ 1500 J/Kg) and an excellent wind profile for severe thunderstorms - forecast cloud base is actually below 700 mb. The forecast for 850 mb (below) valid at 3:00 pm indicates convergence between the easterlies and dry westerlies just out to west of metro area - almost like a Plains dryline situation.

If storms develop this afternoon, the location of this convergence zone will be critical. The WRF-GFS forecast of composite radar echoes at 4:00 pm (bottom) indicates that strong storms do develop over the western metro - exactly where first storms form will be the important forecast issue this afternoon.

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