Wednesday, December 14, 2016

Update on the Approaching Storm

Strong warm fronts of the type we are experiencing today are less common in Utah than they are in the eastern United States.  Today in the Salt Lake Valley reminded me a good deal of the type of weather I experienced in my youth in upstate New York.  Damp, grey, and somewhat raw.

Meanwhile, friends have reported a fun graupel-filled day in the mountains.  As of 4 PM this afternoon, the water equivalent at Alta-Collins since midnight is up to 0.38" and Snowbasin Middle Bowl 0.78".  Warm fronts often feature high stability and that is indeed the case this afternoon with a temperature of 36ºF at the Salt Lake City Airport, 36ºF at the Big Cottonwood S-curves, 34ºF at Spruces, and 31ºF at the base of Solitude.

There's very little change in the forecast for the big event tomorrow night and Friday.  As shown in the 1800 UTC NAM forecast below, temperatures and snow levels (typically about 1000 feet below the wet-bulb zero level at upper right) are expected to remain quite high through Thursday night, lower gradually late Thursday night and early Friday, and then drop more rapidly with the approach and passage of the front Friday afternoon.  At their highest, snow levels will probably peak at about 8000 feet in the central Wasatch early Thursday night.  Juicy atmospheric river conditions with bring high precipitation rates through Friday morning, afterwhich a strong cold front will keep things going Friday afternoon .  Water totals being produced by the NAMfrom Thursday afternoon through Friday evening remain impressive and exceed 2 inches at the Alta-Collins grid point.

Thus, this looks like another good base builder for the upper elevations.  The mid elevations are going to see some rain, but should recover with the frontal passage.  Lower temperatures should yield a transition to drier snow Friday afternoon.

And speaking of lower temperatures, Saturday looks brutally cold with a 700-mb temperature of about -20ºC (even colder in the NAM), which is about as cold as it gets around here.

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