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Area forecast discussion 
National Weather Service Portland or
914 am PST Thursday Nov 26 2015

Synopsis...a blocking pattern continues over the Pacific northwest
with an upper high along the southern b.C. Coast that will move
inland into b.C. Through the remainder of the week and the
weekend...and an upper low over the northern Great Basin that will
wobble around before moving east early next week. This will result in
dry offshore flow not only near the ground but also aloft through
much of the Thanksgiving weekend. The dry pattern may break down as
early as next week but with low confidence in this timing at this

Short term...skies were clear except for some patchy fog and low
clouds near Kelso and south of Eugene this morning. Temperatures this
morning were cool with a lot of 20s in the lower elevations...with 20
so far at Hillsboro being the coldest report. There were a few teens
reported at remote higher elevations in the Cascades.

The offshore wind pattern we are currently under will continue for
several more days...with dry weather expected through the
Thanksgiving weekend. We have a blocking pattern with an upper high
along the southern b.C. Coast and an upper low over the northern
Great Basin and another low well offshore near 145w. This is an Omega
block...but it will transition to a Rex block as the upper high moves
into southern b.C. Through Friday and Saturday. The net result is a
relatively widespread offshore wind event due to a northeasterly flow
aloft across the region between the upper high to our north and the
upper low to our southeast. We will see winds gusting up around 45
miles per hour or so at higher elevations in the mountains. Gradients through
the Columbia River gorge are forecast to reach around 8 mb or
look for gusts to 60 miles per hour or so at Rooster Rock or Corbett...and
higher at Crown Point. Winds will be quite breezy in the Portland and
Vancouver metropolitan areas as well. The strongest winds in The Gorge and
the metropolitan area will be tonight into Saturday. The winds in the higher
elevations will ease this weekend.

Look for clear and cool conditions over the area. Nighttime temperatures at
lower elevations will be down in the 20s in areas where the winds
decouple at night...and a few upper teens are not out of the

Fog or freezing fog will be at a minimum the next couple of days...
with anything that forms mainly near Kelso and south near Eugene. We
might start to see an increase late in the weekend or early next
week. We may also start to see some low clouds or fog developing near
Hood River and Parkdale either Friday morning or Saturday morning.

Long changes. Previous discussion follows...
Saturday night through Wednesday...blocking pattern keeps high
pressure over our area...meaning dry and cool conditions through the
weekend. GFS has trended back toward breaking down the Rex block
earlier and bringing rain back in Monday night in to Tuesday. Am a
bit skeptical because the European model (ecmwf) is holding on to a slower solution
and models tend to try to break these blocking patterns down too
early. If the GFS does pan out...we may return to an active weather
pattern with multiple chances of rain and snow starting Monday night
through the rest of the week. If the European model (ecmwf) is correct...blocking
pattern doesn't break down and bring precipitation back into the area until
later in the week. Hedging toward a blend of the two...with precipitation
returning later on Tuesday or Wednesday. -McCoy

Aviation...VFR conditions next 24 hours. Offshore gradient will
strengthen through the Columbia River gorge resulting in gusts of
30-40 knots at the west end of the Columbia Gorge after 18z Thursday through
Friday. Gusts to 15 to 20 knots possible elsewhere across local forecast
area today...decreasing late tonight.

Kpdx and approaches...VFR conditions next 24 hours. Breezy east winds
develop late this morning...with strongest gusts near 35 knots for
eastern approaches particularly kttd. Bowen/26

Marine...east-northeast over the coastal waters continue as a
thermal trough extends northward into SW Oregon coastal area. Winds
have not picked up this morning with the thermal trough but will
likely pick up this afternoon with increasing offshore
have pushed Small Craft Advisory for winds to 4 PM and included all
marine zones. Should see winds drop off at least briefly early
Friday...but will have to reassess this afternoon any need for Small
Craft Advisory for winds during the day Friday. Offshore gradient
begins to weaken Friday but east winds remain through much of the

Model solutions begin to diverge Monday with the European model (ecmwf) holding on to the
strong high pressure over NE Pacific while GFS trends toward a more
progressive pattern witch brings a 1003mb low off the Oregon coast
Monday afternoon. For now favor the European model (ecmwf) and have weighted the forecast in
that direction. Stronger systems are more likely approach the pacnw
later in the week as GFS and European model (ecmwf) are more similar then.

Seas around 5 to 7 feet through early sun with longer period swell
around 14 to 17 seconds. Seas gradually increase Sun night but exact
swell height is uncertain due to model disagreements. Bowen/26

Pqr watches/warnings/advisories...
Pz...Small Craft Advisory for winds from 4 PM this afternoon to
4 am PST Friday for coastal waters from Cape Shoalwater Washington
to Florence or out 60 nm.



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This discussion is for northwest Oregon and southwest Washington
from the Cascade crest to 60 nautical miles offshore. The area is
commonly referred to as the forecast area.

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