ZCZC SPCSWOMCD ALL
ACUS11 KWNS 272331 
SPC MCD 272331 
CAZ000-280530-

Mesoscale Discussion 0041
NWS Storm Prediction Center Norman OK
0531 PM CST Wed Jan 27 2021

Areas affected...Sierra Nevada

Concerning...Heavy snow 

Valid 272331Z - 280530Z

SUMMARY...Heavy snowfall rates in the 3-5 inches per hour range are
likely this evening for the western slopes of the Sierra,
particularly in areas of 4000-8000 ft elevation.

DISCUSSION...Water-vapor imagery late this afternoon shows a
mid-level trough situated over the eastern Pacific west of the OR
and northern CA coasts.  The low, mid, and high-layer
moisture-sensing GOES imagery bands indicate a deep tropospheric
fetch of substantial moisture optimally oriented from the eastern
Pacific northeastward into the Sierra Nevada.  

The thermally direct circulation of an upper speed max will continue
to be located over the Sierra Nevada through tonight.  Coupled with
the strong large-scale ascent, orographic forcing will result in
strong upward vertical motion on the western slopes of the Sierra. 
The aforementioned Pacific moisture will contribute to a strong
moisture flux in the region as lessening static stability/latent
heating occurs near the western slopes as precipitation rates
increase this evening.  Model guidance indicates snowfall rates on
the western slopes between 4000-8000 ft elevation will range from
3-5 inches per hour.  During some of the heavier precipitation
bursts, appreciable spillover snowfall later this evening may occur
on the lee side near the CA/NV border.

..Smith.. 01/27/2021

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

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

LAT...LON   36731861 36781881 37571955 38532045 38922057 39042034
            38791985 38491962 37581894 36971846 36731861 

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