Wednesday, February 20, 2013

Quick Status Report Based On Early WRF

At 6 am MST this morning the cold front, associated with the closed 500 mb low over southern California, was just moving into western Arizona. However a rain band was developing over southwestern Arizona, and the front will likely jump to the leading edge of this precipitation area. The early run of the WRF-GFS model continues to forecast the main band of precipitation to cross eastern Pima County between 10 am to noon (above forecast of composite radar is valid at 11 am). The forecast surface plot (below) is valid at the same time. Very cold and windy with the band.

The model forecasted sounding for TUS at 11 am is shown above. The surface-based layer that is above freezing is deeper than was forecast yesterday. So, if this forecast verifies, the band of precipitation may produce a burst of heavy snow across the metro. The deeper warm layer makes it tougher to call this situation. Will just have to watch how things evolve this morning. There are few observations out to our west, so there won't be much to watch except radar, until the precipitation moves into eastern Pima County. Total precipitation remains similar to the previous forecasts shown earlier (total valid through midnight is shown below). The amounts are light again at low elevations, but with a significant snow event in the mountains.

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