Mesoscale Discussion 0042
   NWS Storm Prediction Center Norman OK
   1200 AM CST Thu Jan 28 2021

   Areas affected...The California High Sierra

   Concerning...Heavy snow 

   Valid 280600Z - 281200Z

   SUMMARY...Very heavy snow with rates of 3-5 in/hr are expected to
   continue overnight across portions of the Sierra Nevada above 4,000
   feet. Blizzard and whiteout conditions may also occur with the very
   heavy snow and strong winds.

   DISCUSSION...Evening water vapor imagery showed a mid-level trough
   across the eastern Pacific and northern California coast. A 60-80
   knot mid-level jet streak was located along the eastern periphery of
   the trough extending onshore into western Nevada. 

   Widespread strong ascent is occurring along much of the West Coast
   with the trough and jet streak manifesting as a strong poleward
   moisture flux in the low and mid-levels. Regional radar and
   satellite observations show a large band of enhanced precipitation
   associated with the strong moisture flux orthogonal to the Sierra
   Nevada Range. Very heavy precipitation is falling with this band as
   confirmed by spotter reports and several ground stations around 7000
   ft MSL (KBAN & KMMH) which have reported continuous heavy snow for
   the last several hours. Heavy snow is expected to continue for at
   least the next 6 hours as; forcing for ascent from the
   aforementioned trough and jet streak continue to move onshore,
   persistent strong orographic ascent from mid-level flow interacting
   with the Sierras, and decreasing static stability/moistening from
   relentless moisture transport into central/southern California. 

   The previously mentioned factors will support very heavy snowfall
   rates of 3-5 in/hr (locally higher amounts possible) from 4000-8000
   ft through tonight. The heaviest snow is forecast to remain across
   the central and southern Sierra, but will likely expand northward
   slightly as the mid-level trough and associated forcing for ascent
   pivot onshore later tonight. Heavy snow may also spill over the
   crest into portions of western Nevada tonight where snowfall rates
   close to 1 in/hr have been observed periodically.

   ..Lyons.. 01/28/2021

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

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

   LAT...LON   39691926 39421952 39201973 38931987 38691971 38461950
               38151916 37891885 37421861 37071863 36911871 37001917
               37281963 37612001 38292038 38852071 39162080 39592072
               39882035 39981988 39921946 39691926