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Mesoscale Discussion 0001
NWS Storm Prediction Center Norman OK
0926 PM CST Tue Jan 02 2024

Areas affected...the Sierra Nevada...from west of Tahoe into areas
southeast of Yosemite

Concerning...Heavy snow 

Valid 030326Z - 030800Z

SUMMARY...Heavy snow rates in excess of 2 inches per hour may begin
impacting the I-80 corridor west of Tahoe by 9-10 PM PST, if not
earlier, before developing southward along the western slopes of the
Sierra Nevada, across and southeast of Yosemite by midnight-1 AM

DISCUSSION...Cloud tops have been cooling the past few hours, inland
of the San Francisco Bay area toward the Sierra Nevada to the west
of Tahoe.  This is occurring downstream of a vigorous short wave
trough, which is forecast to continue gradually pivoting across and
inland of the central California coast through 06-09Z., accompanied
by considerable further strengthening of large-scale ascent.  Models
indicate that strongest lift will focus along a frontal zone already
in the process of advancing inland, south/east of the Bay area and
into the northern Sierra Nevada, and within an increasing upslope
flow component across the western slopes of the northern into
southern Sierra Nevada by late evening.

Coupled with saturating thermodynanmic profiles, including
precipitable water in excess of .4 to .5 inches, strengthening lift
through through mid-levels with favorable cold temperatures for
large dendritic ice crystal growth (roughly between 700-600 mb in
forecast soundings) appears likely to yield intensifying snow rates.
 By 05-06Z, if not before, guidance generally indicates that this
may include rates in excess of 2 inches per hour near the Interstate
80 corridor, where cold advection may result in snow levels falling
to near or below 4000 feet.   

As the strengthening lift develops southward along the mountains
into and southeast of the Yosemite vicinity through 08-09Z, snow
levels are likely to be higher (on the order of 4500 to 5000+ feet),
at least initially, before gradually falling overnight.  However,
somewhat higher moisture content may support heavier peak rates
approaching or exceeding 3 inches per hour.

..Kerr.. 01/03/2024

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


LAT...LON   39282034 38832002 38131950 37361936 37671975 38162027
            38772070 39082082 39282034 

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