ZCZC SPCSWOMCD ALL
ACUS11 KWNS 132301 
SPC MCD 132301 
CAZ000-NVZ000-140300-

Mesoscale Discussion 2025
NWS Storm Prediction Center Norman OK
0501 PM CST Mon Dec 13 2021

Areas affected...the central Sierra

Concerning...Heavy snow 

Valid 132301Z - 140300Z

SUMMARY...Snowfall rates in excess of 2 inches per hour are expected
above 5000 to 5500 feet with snowfall rates possibly as high as 4
inches per hour above 6000 feet.

DISCUSSION...A strong atmospheric river has been bringing
low-elevation heavy rain and mountain snow to much of northern and
central California through the day today. Cooler air has moved in
aloft with snow levels now dropping below 5500 feet based on central
Sierra observations. Expect these to continue to fall through the
evening. Simultaneously, a renewed push of heavy precipitation can
be seen on composite radar reflectivity across coastal and central
California around 2230Z. In addition, guidance indicates the
low-level jet is expected to strengthen from around 50 knots to 55
to 60 knots and veer more southwesterly. This will lead to
increasing upslope flow which will further enhance already heavy
precipitation. Therefore, very heavy to extreme snowfall rates are
expected with the greatest rates expected between 23Z and 08Z.

..Bentley.. 12/13/2021

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

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

LAT...LON   38061899 37411838 36881836 36851895 37451961 37952006
            38622053 39092068 39612093 39872075 39812046 39472020
            39251999 38931986 38641956 38381927 38061899 

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