Friday, February 25, 2011

Quick Update On Weekend Storm

The satellite PW image for the east Pacific this morning (Friday February 24) indicates that the strong, short-wave trough off of Oregon and northern California coasts has managed to tap into the moisture plume north of Hawaii. Extent to which this moisture feed will continue during next 48-hours will be an important factor in determining the final QPF amounts from this storm.

The models are all in agreement that this system will swing through Arizona Saturday afternoon into Sunday afternoon. Primary issues at this time: timing - models have been tending to slow down the system a bit. Most of the models do agree that the storm's main impact across southeast Arizona will occur between midnight and noon on Sunday. How cold will the 1000-500 mb thicknesses get as the 500 mb cold air moves by? Shown in middle two panels are: GFS operational forecast from midnight  for noon Sunday with thickness in Tucson area of about 534 dm; this morning's NAM forecast (lower of two panels) for 5 am Sunday morning indicates similar thickness values moving toward the Tucson area. So, how low will the snow line come Sunday morning? I'd like to see values below 534 dm for flakes at the house - so it will be close.

The bottom graphic is from the Atmo WRF-GFS midnight run. This model forecasts the snow accumulations (contours are in inches of snowfall) through Sunday to remain around the fringes of the Tucson metro area, i.e., about 3000 ft msl. Of note, the model forecasted snow in the Tortolitas, where the big golf tournament is underway. The model also forecasts a fairly significant snowfall across the southeast Arizona grasslands from Santa Cruz County and Nogales up toward Benson - will there be enough snowfall to ice over the highways (I know from experience that Highway 83 can become treacherous between I-10 and Sonoita)? Heaviest snowfall is predicted by the model to occur on the Catalinas and Rincons, where amounts approach 20 inches. We're now in the wait, watch, and observe mode as February 2011 brews up its second major winter storm.

No comments:

Post a Comment