ZCZC SPCSWOMCD ALL
ACUS11 KWNS 130155 
SPC MCD 130155 
ORZ000-130700-

Mesoscale Discussion 0071
NWS Storm Prediction Center Norman OK
0755 PM CST Fri Feb 12 2021

Areas affected...Portions of Willamette Valley

Concerning...Freezing rain 

Valid 130155Z - 130700Z

SUMMARY...Freezing rain rates are expected to increase this evening,
especially within the 7-11 PM time window. Areas within the
Willamette Valley west of Portland are most likely to see higher ice
accumulations. Precipitation in Portland will remain snow with a
transition to freezing rain and sleet towards early Saturday
morning.

DISCUSSION...Surface high pressure into the Columbia Basin has
helped to maintain easterly/northeasterly surface winds into the
Willamette Valley. With the approach of a strong Pacific trough this
evening, coverage and intensity of precipitation should increase.
Current KRTX reflectivity trends indicate that this process is
underway. Light freezing rain has been observed for several hours
from just west of Portland and southward to near Salem. These areas
are the most likely to see larger ice accumulations. While Portland
is currently observing snowfall, it will be near the transition zone
to freezing rain/sleet. Forecast soundings do indicate that freezing
rain and sleet are possible towards 2-4 AM PST. The exact evolution
of the transition zone will be dependent on the surface low
developing west of the Washington coast. Current observations
indicate a preference for a more northerly track which would
indicate higher probability of transition away from snow later
tonight. While heavy snow is also possible with this trough, the
heaviest snowfall rates are expected to remain within the Cascades
northward into the western Puget Sound and adjacent Olympic
Peninsula.

..Wendt.. 02/13/2021

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

ATTN...WFO...PQR...

LAT...LON   44962350 45882353 45962340 45972315 45762290 45452279
            44872297 44622317 44582338 44732347 44962350 

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