South Washington Cascade Foothills
... Freezing rain remains a growing possibility Thursday and
Thursday evening in the inland areas of southwest Washington and
A strengthening upper low over the Gulf of Alaska will bring a
threat for freezing rain reaching the coast late on Thursday
morning and then spreading inland Thursday afternoon and evening.
The most likely scenario brings a rather short lived event with
the primary focus across an area mainly north of Wilsonville.
There would be a few hours of ice accumulation followed by gradual
warming above freezing. Amounts of ice accumulation would most
likely be two tenths of an inch or less... typically not enough to
produce major damage.
However... there is a fair amount of uncertainty with this system
in both timing and whether the bulk of the Willamette Valley
receives the freezing rain. The main unknown at this time centers
around how quickly the lower level cold air mass and morning fog
and low clouds break up... and whether southerly winds above the
1500 foot level drop to the surface and scour out the cold pool
like most models want to illustrate. If the cold air does not
scour out... the full potential of this event could materialize
with valley locations remaining under the influence of a cold pool
for longer than a couple hours. If so... then somewhere between one
quarter and one half an inch of ice may produce notable damage to
trees and power lines plus the obvious threat to Road surfaces.
Even under the worst case scenario... feel all areas will warm
above freezing by later Thursday evening. Would expect the
Columbia Gorge to be the last place to warm... possibly not until
later Thursday night and Friday morning.
This is a difficult forecast as weather models rarely handle the
vertical temperature erosion accurately. Please continue to follow
the latest forecasts as this situation evolves.
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