Warm, Wet, and Windy

Posted Wednesday, March 21st, 2018 by Peter Veals

As Lucas mentioned, a storm is bearing down on us that promises a period of warm and wet “atmospheric river” conditions. The action will start early Thursday, with the rain/snow line somewhere around 9,000ft, heavy precipitation rates, and winds gusting to near 100mph on the high peaks (50 mph mid mountain at the resorts). Late Thursday into Friday morning, the snow levels will be dropping and the winds will start backing off as colder air works into the region. I expect snow levels to reach about 6-7000ft by Friday morning and remain somewhere around there through the day. The precip should taper off by late Friday.

GFS model meteogram
The meteogram for today’s 6Z run of the GFS model lays things out nicely. Note the heavy precip beginning Thursday and the snow levels starting high and lowering slowly through the event. weather.utah.edu

It looks like the upper Cottonwoods can expect 1.5-2.5″ of liquid, with places like the northern Wasatch around Ben Lomond Peak and the southern Wasatch around Timpanogos likely to get something more like 2-4″ of liquid. Above 9,500ft this should be all snow, and with an average of 8:1 or 10:1 ratios for the storm, that should equate to 1-2ft of snow for the tops of the upper Cottonwoods resorts and 2-3ft of snow for the top of Snowbasin. However, a very large chunk of the skiable terrain in the Wasatch is below 9,500ft, so expect a rain-slush-snow transition throughout the storm with maybe 6-12″ of new snow at 8,000ft by the time all is said and done.

Precip forecast from the U of Washington’s WRF model. I generally take these amounts as a reasonable, but higher-end scenario. Note the widespread >2.5″ for the Wasatch (sorry for the worst unit scale ever).
ECMWF model
Precip forecast from the more conservative ECMWF model. I usually consider these as extremely likely to verify, but often slightly low. models.weatherbell.com

We briefly clear out and warm up on Saturday, and then the next, colder storm is lined up for Sunday.

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