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Mesoscale Discussion 0092
NWS Storm Prediction Center Norman OK
0815 PM CST Sat Feb 09 2019

Areas affected...Northern Sierra Nevada

Concerning...Heavy snow 

Valid 100215Z - 100615Z

SUMMARY...Heavy snow rates of 2-3+ inches per hour will continue to
develop across the northern Sierra Nevada (into elevations as low as
2000-2500 feet) through 7-10 PM PST, before gradually shifting
southward into the southern Sierra Nevada overnight.  Gusty winds
will create considerable blowing and drifting, and sharply reduced

DISCUSSION...An initially deep lower/mid tropospheric cyclone is
forecast to begin migrating or redeveloping inland of the Oregon
coast, and east of the southern Cascades this evening into the
overnight hours.  It may weaken as it does, but guidance indicates
that a significant short wave impulse will pivot around its
southwestern periphery into/through much of northern California
between now and 06-09Z.  

Ahead of the associated cold front, flow is already strengthening
out of the southwest, from mid to lower levels (including 40+ kt to
around 850 mb), across the northern California coastal ranges and
Sacramento Valley into the northern Sierra Nevada.  In the presence 
of a cold (and cooling) environment (including freezing levels
falling to 2000-2500 feet), strengthening orographically forced
ascent is contributing to intensifying snow rates across the
northern Sierra Nevada.  This is occurring within a pre-frontal
plume of modest moisture (including precipitable water up to around
.5 inches) advecting off the mid-latitude Pacific.

Latest Rapid Refresh forecast output suggests that snow rates may
increase up to 2-3+ inches per hour along the Sierra Nevada, west
through southwest of Tahoe Valley, between now and 03-06Z, before
the heaviest snow slowly begins to shift to the southwest of Tahoe
Valley and into the southern Sierra Nevada between 06-09Z.

..Kerr.. 02/10/2019

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


LAT...LON   40082141 39392034 38711990 38301960 37932007 38152048
            38782083 39702168 40082141 

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