Tuesday, January 17, 2017

500 mb - Cold, Colder, And Then Much Colder

The global models continue to be very consistent, forecasting a series of Pacific short waves and cold fronts to cross the Southwest during the coming week. I've taken a quick look at 00 UTC WRF-GFS forecasts out through a week, even though that's a bit dangerous. The GEFS plumes for QPF at TUS (above from 06 UTC last night) forecast two 100 % events at the airport - one on Thursday night, rapidly followed by a more significant event Friday night into Saturday, and then there's a more scattered event at the start of next week.Several of the GEFS members are forecasting some snowfall at the airport - this was the case with an earlier event this winter that melted away as it got closer in time.

The forecasts of the temperatures at 500 mb associated with these short waves is very impressive and very cold over Arizona. The forecast at top of these three panels (all on the 5.4 km grid) is valid at 03:00 am MST on 20 January; the one directly above is for 10:00 am on the 21st; and the forecast below is valid at 10:00 pm on the 23rd (next Monday). Temperatures with these short waves range from -25 C to colder than -35 C. I don't remember when 500 mb temperatures colder than -30 C last occurred at TWC. 

Just for fun, here are the model's forecasts of precipitation (from 00 UTC on the 1.8 km grid) out through the next week (i.e., 05:00 pm on Tuesday the 24th. Total precipitation shown above.. while forecast below is for snowfall during that period. The model forecasts some snow over the grasslands east of the Santa Ritas and also along I-10 at several places east of Tucson. Will watch how all this unfolds in the real atmosphere during what should be an interesting week.

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