Mesoscale Discussion 0065
NWS Storm Prediction Center Norman OK
0542 PM CST Tue Jan 17 2017
Areas affected...Portions of northwest Oregon and southwest
Washington
Concerning...Freezing rain
Valid 172342Z - 180545Z
SUMMARY...Moderate to locally heavy freezing rain rates are possible
into the evening from the central/northern Willamette Valley through
the Columbia River Gorge into adjacent parts of the Cascades.
DISCUSSION...At 2330Z, the leading edge of a substantial
precipitation shield is moving into western Oregon and Washington. A
continuous feed of moisture ahead of an upper trough off of the
Pacific Northwest coast will maintain moderate to locally heavy
precipitation rates through tonight. Meanwhile, drainage of cold air
from the east through the Columbia Gorge is maintaining subfreezing
temperatures from the southern WA Cascades westward to the
central/northern Willamette Valley. The KPDX ASOS site has reported
0.20 inches of ice accretion over the last two hours, with nearby
sites reporting at least 0.05 inch-per-hour rates. Rates of
0.05-0.10 inches per hour will spread eastward with time this
evening, leading to significant ice accumulations.
Some erosion of the shallow subfreezing layer is possible this
evening across the western portion of the MCD area, including the
Portland metro area. However, with a relatively strong pressure
gradient being maintained and very cold temperatures across portions
of eastern Washington and northeast Oregon, temperatures will be
very slow to rise as strong easterly flow through the Gorge
continues.
..Dean.. 01/17/2017
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...PDT...PQR...
LAT...LON 45712314 46002288 46082264 45852229 45862196 46132127
46282094 46302061 45692049 45492062 45452123 45522152
45522176 45512199 45452221 45392240 45302269 45172311
45422320 45712314
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