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Area forecast discussion 
National Weather Service Portland or
217 PM PST Sat Nov 28 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 Rex block continues over the Pacific northwest this
afternoon...with an upper level high over southern b.C. And an upper
low over the Great Basin. This continues to result in decent 30 to 40
knots northeast flow aloft across southwest Washington and northwest and
brisk offshore surface gradients...currently around 6 mb through The
Gorge. Thus we continue to have breezy conditions in much of the
area...with a bit more wind at higher elevations and stronger winds
in The Gorge. This has resulted in another day with plenty of
sunshine and temperatures trying to reach 50 again especially in the
breezier areas. The far South Valley just crossed 40 degrees after
falling to 18 at Eugene and to 19 at the Corvallis AWOS this morning.

This pattern will continue tonight into Sunday...but then The Block
will begin to weaken and move east late Sunday and especially Monday.
The offshore flow event will continue through Sunday...but we will
begin to lose the winds aloft on Sunday and the winds will become
more of a gap flow event...especially concentrated through the
Columbia River gorge. As a result...we will see more low clouds near
Hood River...and we will start to see more areas of fog and freezing
fog and low stratus in the inland valleys Sunday morning and
especially Monday morning.

The low level air mass will remain lows Sunday and Monday
mornings will remain similar to what we have seen the last 3 mornings
or so. An exception may be that the coast will start to warm a bit
Monday morning.

Attention then turns to the first weakening/splitting system forecast
to move through southwest Washington and northwest Oregon Monday and
Monday evening. The models have now been consistent with this
solution for the last day or so of model confidence is
increasing. The main energy with this next system will be heading
well north toward the central and north b.C. Coast. The
weakening/splitting/dying southern end of a front will approach the
coast Monday morning...move onshore Monday afternoon...and through
the forecast area Monday evening. The highest probability of precipitation will be at the
coast...dwindling farther inland as the system weakens and falls

We could see a tenth or two of an inch at the coast and on the west
slopes of the Coast Range...but inland looks like a trace to a few
hundredths of an inch at most.

The biggest problem with the Monday system is that it will again be
very cold Monday morning inland...after which the clouds will
increase and reduce any solar heating. Some light precipitation will
likely fall that could be mixed winter type precipitation. The best
chance of this is in The Gorge...and the precipitation could be
mostly snow near Hood River. But some threat of rain mixed with snow
is possible in the valleys as well. The low level air mass is quite
dry inland and evaporation/sublimation will inhibit precipitation
amounts. Amounts look very light impacts look minimal at
this point. Freezing rain looks unlikely at this point except perhaps
near Hood River as low level temperatures will be cool but probably a little
above freezing once the precipitation starts. The precipitation
should mostly end after the evening hours as the system moves east of
the Cascades.

A good part of Tuesday looks dry...though the next system may start
to bring some rain to the coast later in the day. Tolleson

Long term...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...00z taf expectations...VFR conds for the next 24
hours. Easterly gorge outflow will bring gusts to around 30 kts
for kttd this evening then easing to 20-25 kts late this evening.
Konp AWOS will apparently be out of service until at least Monday
and not likely much of an issue due to minimal cloud cover until
after 30/06z. Generally plan on some form of east to southeast
winds with speeds 8g18kt until then.

Kpdx and approaches...VFR. Weak low level wind speed shear is
possible for the rwy 10 l/r approaches from gusty Columbia Gorge
outflow. /Jbonk


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 Sunday afternoon 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

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.

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 Wednesday
with the far outer waters touching on 20 feet under stronger winds
while the inner waters will see 16-18 feet that day. /Jbonk


Pqr watches/warnings/advisories...
Pz...Small Craft Advisory for winds from 8 am Sunday to 4 PM PST
Monday for waters from Cape Shoalwater Washington to Florence or
from 10 to 60 nm.

Small Craft Advisory for hazardous seas from 10 am Sunday
to 4 PM PST Monday for waters from Cape Shoalwater Washington to
Florence or from 10 to 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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