Friday, March 08, 2013

Friday Morning - Storm progress

At 6 am MST this morning the middle and upper-level cyclone is over the Pacific, west of southern California (see 13 UTC IR satellite image above). The first band of showers and thunderstorms has bypassed much of the Tucson area, staying south toward Green Valley. The morning sounding taken at TWC (Tucson NWS Office on campus) had serious data problems (below) and has a reported 500 mb temperature that is too low by several degrees C. (Eventually the unreliable Sippican sondes will be be replaced - see earlier post.) The wind profile is quite strong and gusty winds were already occurring across parts of the metro area before sunrise. Graphic below the sounding shows the composite reflectivity from the NWS Tucson radar at 6:23 am this morning - apparently a thunderstorm moved near Green Valley with the first band of showers.

I show the early WRF-GFS forecasts of total precipitation and total new snowfall through 5 pm MST on Saturday 9 March. The graphic above is the forecast for precipitation on the regional, 5.4 km forecast grid. Note the Tucson metro minimum. Below is the snowfall forecast from the high-resolution 1.8 km grid. The area of the Rim just north of Payson is forecast to receive around two feet of new snow by the model. Lesser amounts forecast for the higher mountains of southeast Arizona. Will be quite a change after yesterday's high of 80F.

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