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Area forecast discussion 
National Weather Service Portland or
240 am PST sun Nov 29 2015

Synopsis...a Rex block will continue through this weekend over the
Pacific northwest with an upper high over southern b.C. And an upper
low over the northern Great Basin. This will result in dry offshore
flow continuing through the rest of the Thanksgiving Holiday weekend.
The dry pattern is looking like it may start to break down during the
first part of next week as an initial dying system moves through the
Pacific northwest Monday. The weather pattern is likely to become
more active during the remainder of the week...with decent systems
moving through Tuesday night and Wednesday and again later in the

Short term...a blocking ridge from southern British Columbia down the coast early
this morning to continue for one more day anyway. With little change
to the overall pattern and a continued offshore flow in the low
levels expect sun to bear a strong semblance to Sat. One difference
today is that there is more low clouds evident on satellite fog
channel in the central gorge and Hood River NAM had
projected. Expect the Columbia Basin stratus to persist through the
rest of the offshore flow...into Monday.

Models in general continue to try and bring a shortwave into the
upper ridge Monday. Normally expect little precipitation to make it
inland with the first system into a ridge...but most models minus
the ec have been persistent in recent runs in bringing at least a
little precpitation inland Monday afternoon. Initial probability of precipitation arrive at the
coast and Coast Range Monday morning...and spread inland in the
afternoon. With the shortwave stretching considerably...and model
cross sections indicating decent low to middle level moisture will
continue to limit probability of precipitation to chance category inland areas for the
afternoon...and limit probability of precipitation to slight chance in The Gorge and north
Willamette Valley due to drying effects of the offshore winds. As
the shortwave brings the first chances for precipitation to the
Coast Range Monday morning after some still Cold Valley low temperatures...
will add the possibility for some freezing rain to north Coast Range Monday
morning. Evaporational cooling may lower snow levels as whatever
precipitation spreads inland in the afternoon. Current wet bulb
temperatures suggest at least some potential for snow levels down into
lower valleys Monday afternoon...mainly from The Gorge west to the west
slopes of the north Coast Range. Will continue mention of mixed type
precipitation there...but low probability of precipitation still indicate the likelihood of
signififcant weather impacts are quite low.

Low probability of precipitation drop off Monday night as the first shortwave lifts north. Next
system is set to arrive late Tuesday. Models in pretty good agreement in
bringing the front to the coast Tuesday evening...although GFS tends to
spread rainfall in a little quicker than other models. For now will
limit probability of precipitation to coast and Coast Range Tuesday afternoon...except allow for
some small probability of precipitation into the S Washington Cascades where SW flow in lower to middle
levels adds a little orographic lift.

Long changes. Previous discussion follows. Tuesday night
through Saturday...the first in a series of more organized storms
will move through Tuesday night and early Wednesday with a better
chance of rain than the Monday system. Snow levels will be rising a
bit with this one as well. This will be followed by another front
later Wednesday night and Thursday. Once this front moves
through...snow levels drop back down in the Cascades as the upper
trough move through around Friday. Another warm front and more
organized system is expected next weekend. All of this activity is
consistent with a rather active pattern currently in the western and
central Pacific. Tolleson

Aviation...VFR next 24 hours dry offshore flow. East winds with
gusts to 30 knots continue to impact kttd today and tonight. Expect
increasing high and middle clouds late Sunday night ahead of next
system. Konp AWOS will apparently be out of service until at least
Monday and not likely much of an issue with expected VFR

Kpdx and approaches...VFR. Gusty east winds through The Gorge
prevail near eastern approaches. Weak low level wind speed shear
is possible for the rwy 10 l/r approaches from gusty Columbia
Gorge outflow through this evening. /26


Marine...high pressure inland and a broad area of low pressure
offshore will keep a decreasing offshore flow component through
early Sunday. A weakening front brushes the waters but still
brings solid Small Craft Advisory level winds followed by wind
wave driven seas to the outer waters late Sunday through Monday
afternoon. A second and much stronger front will likely cross
Tuesday afternoon and evening. This front will have a
strengthening surface low swinging northeast and just inside of
130w. This gives confidence that gales will occur at least as
early as Tuesday daybreak and peaking Tuesday afternoon and
evening. So a gale watch has been issued for this event.

Another pair of systems swing across the area Wednesday and
Thursday each bringing potential gales. There is a bit of a
relative break Friday before another couple systems potentially
crossing Saturday and Sunday. However details are not well defined
at this time due to model run-to-run variations.

This stream of systems will bring elevated seas to the waters with
this immediate 24 hours likely being the last time where they are
below 10 feet and likely staying closer to 15 feet through the next
5-7 days. For now it appears the peak seas will occur late
Wednesday and Thursday with the far outer waters touching on 20
feet under stronger winds while the inner waters will see 16-18 feet.


Pqr watches/warnings/advisories...
Pz...gale watch from Tuesday morning through Tuesday
evening for waters from Cape Shoalwater Washington to
Cascade Head or from 10 to 60 nm-waters from
Cascade Head to Florence or from 10 to 60 nm.

Small Craft Advisory for winds from 7 PM this
evening to 4 PM PST Monday for waters from
Cape Shoalwater Washington to Cascade Head or from
10 to 60 nm-waters from Cascade Head to Florence or from
10 to 60 nm.

Small Craft Advisory for hazardous seas from
noon today to 7 am PST Tuesday for waters from
Cape Shoalwater Washington to Cascade Head or from
10 to 60 nm-waters from Cascade Head to Florence or
from 10 to 60 nm.

Small Craft Advisory for hazardous seas from
10 am Monday to 4 am PST Tuesday for coastal waters from
Cape Shoalwater Washington to Cascade Head or out 10 nm-
coastal waters from Cascade Head to Florence or out 10 nm.

Small Craft Advisory for rough bar in effect from
5 PM this afternoon to 10 PM PST this evening.



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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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