Monday, April 26, 2021

Desperately Needed Spring Storm Today

Rain and upper elevation snow are falling across much of northern Utah today as a slow moving front moves across the region.  We desperately need the precipitation and right now it looks like a pretty good soaker.  

The latest radar imagery shows pretty solid coverage (given the limitations of the radar due to the region's complex terrain).  This includes strong returns over the central Wasatch.  

Surface observations within an hour of 1441 UTC (0841 MDT) show the shallow surface front draped across the central Salt Lake Valley with northwesterly flow at the Salt Lake City airport and in the West Valley region and southerly flow in Draper and Herriman.  

Source: MesoWest

This leading nose of the front is, however, shallow and the flow became southwesterly in the morning (0600 MDT) sounding at an elevation of only 7000 feet.

Source: SPC

Thus, most of the precipitation is being generated this morning in the southwesterly flow, which is quite juicy.  The sounding above shows nearly saturated flow through the troposphere and the analysis below shows a narrow filament of high integrated vapor transport, known commonly as an atmospheric river, extends inland across southern California, Nevada, Utah, and Wyoming.  

Source: CW3E

Snow levels in the mountains are currently high.  Temperatures at 8 am in Little Cottonwood Canyon were 35˚F at 7688 feet, 30-34˚F at observing sites near the base of Alta, and 23˚F at the top of Mount Baldy (11,000 feet).  The web cam image below, taken at about 0855 MDT, suggests wet snow is falling at least down to the tram base as there appears to be slush on the bypass road.  

Still, it's surely a wet-sponge day out there.  Hard-shell recommended if you are braving the cream-on-crust conditions this morning.  

The models suggest precipitation will continue for most of the day today in the Salt Lake Valley and the central Wasatch.  This agrees well with the slow moving precipitation field evident on radar this morning.  The 0600 UTC GFS puts out 0.76" of water equivalent and 7.6" of snow with a high average water content of 10% high-density for Alta through 5 PM.  Temperatures and snow levels will, however, lower slowly today.  My best guess would be 4-8" of high-density cream above 9000 feet through 5 PM.  Numbers could be higher if we transition to lower density snow this afternoon, but there's too much favoring high density in this one.  

Note also that we could see some thunder this afternoon to spice up the day.  

There could be some snow showers tonight and tomorrow, although the models right now are bringing in some dry air at mid levels and are not bullish on mountain precipitation other than perhaps a couple of inches in favored locations.  

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