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SPC MD 1806

SPC MD 1806

December 24, 2017 Safety Weather 0

MD 1806 CONCERNING FREEZING RAIN FOR PORTIONS OF NORTHWEST OR AND SOUTHWEST WA

MD 1806 Image

Mesoscale Discussion 1806
NWS Storm Prediction Center Norman OK
1149 AM CST Sun Dec 24 2017

Areas affected...portions of northwest OR and southwest WA

Concerning...Freezing rain 

Valid 241749Z - 242045Z

SUMMARY...Freezing rain, with accumulations of 0.05 to 0.10 inches/3
hours will likely develop north across the Willamette Valley,
western Columbia River Gorge and the Portland Metro area over the
next few hours.

DISCUSSION...An area of mixed precipitation continues to move
northeast across far northwest OR/southwest WA at 1735Z aided by
low-level warm advection and a pronounced moisture feed in advance
of a cold front currently near 128 degrees W longitude.  As this
area of precipitation develops northward towards the Portland Metro
area, wet-bulb cooling effects (surface dew points currently in the
upper teens) should result in surface temperatures lowering to at or
below freezing in the next few hours.  This will result in freezing
rain mixed with sleet as the dominant precipitation types across the
Portland Metro and adjacent Willamette Valley/western Columbia River
Gorge.  Ice accumulation rates of 0.05 to 0.10 inches (locally
higher) in 3 hours will be possible.

..Bunting.. 12/24/2017

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

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

LAT...LON   44982293 45132303 45762316 46122285 46252239 46052217
            45702201 45132187 45002219 45002258 44932291 44982293 

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