Mesoscale Discussion 0055
   NWS Storm Prediction Center Norman OK
   0123 PM CST Thu Jan 16 2020

   Areas affected...Northern Sierra Nevada

   Concerning...Heavy snow 

   Valid 161923Z - 162230Z

   SUMMARY...Heavy snow, at rates up to 2-3 inches per hour, are
   expected to develop southward along the western slopes of the Sierra
   Nevada, across and south of Interstate 80 through the Yosemite
   vicinity, by 2-4 PM PST.  This will be accompanied by strong gusty
   winds and periods of sharply reduced visibilities.

   DISCUSSION...A vigorous short wave trough is in the process of
   progressing inland of the northern and central California coast, and
   forecast to continue across the Sierra Nevada by early this evening.
    Strongly divergent upper flow ahead of this feature, coupled with
   low-level forcing along an associated cold front, is contributing to
   a band of heavy precipitation which is now beginning to overspread
   the northern Sierra Nevada.

   The front appears preceded by a narrow jet of 30-50 kt southwesterly
   flow in the 850-700 mb layer.  Although some weakening is forecast
   through the afternoon, an associated influx of higher moisture
   content (precipitable water of .5-.7+ inches) appears likely to
   continue into the western slopes of the Sierra Nevada.

   Near/just ahead of the front, models suggest that forcing for ascent
   along the western slopes of the Sierra Nevada will continue to
   strengthen, including within the favorable mixed-phase layer for
   dendritic ice crystal growth.  This will likely aided by increasing
   orographic forcing, and perhaps a zone of enhanced lower/mid
   tropospheric warm advection. 

   It appears this probably will include snow rates increasing to 2-3
   inches per hour, particularly near and above 4000 feet initially,
   before snow levels lower to near or just below 3000 feet with the
   eastward progression of the front.  Heaviest snow rates are expected
   to commence across and south of the Interstate 80 corridor between
   now and 20-21z, before gradually shifting southward, across and
   south of the Yosemite vicinity by 22-00Z.

   ..Kerr.. 01/16/2020

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...REV...HNX...STO...

   LAT...LON   39932103 38822007 38121952 37281894 37261997 38132055
               39422160 39932103