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Area forecast discussion
National Weather Service Portland or
232 PM PST Tue Nov 21 2017

Synopsis...wet and unsettled weather will continue this week. A warm
front was lifting north through northwest Oregon and southwest
Washington this morning, ushering in more rain. Expect some windy
conditions near the coast this afternoon. A trailing cold front will
linger over the forecast area tonight and Wednesday for more rain,
especially near the coast and in the north interior areas. Snow
levels in the Cascades will remain relatively high. The next cold
front sweeps through on Thanksgiving with snow levels in the Cascades
lowering close to the passes Thursday night and Friday. Look for some
lingering showers Friday before the next system arrives on the
weekend with rising Cascade snow levels. Look for snow levels
lowering back near the Cascade passes again Sunday night and Monday.

Short term...tonight through Friday...National Weather Service
Doppler radar continued to show precipitation over much of southwest
Washington and northwest Oregon this afternoon associated with a warm
front the was moving north through the forecast area. There was some
drying down in the inland portion of Lane County this afternoon as
the warm front lifts north. The freezing level was 10300 feet at
Salem this morning, so it is pretty much rain everywhere except on
the higher peaks. The warm front is forecast to continue to move
north this afternoon and tonight, but a trailing cold front will then
be draped over the area tonight and Wednesday, with the greatest
likelihood of rain along the coast and in the north interior areas as
we get further into Wednesday.

The models still show a good amount of wind south of the warm front
over the coastal waters as we go through the day today, with the peak
this afternoon. We should see some good winds along the coastal
headlands and beaches, but it is not clear whether we can reach
warning criteria. Will continue to stay with the current forecast of
just under warning criteria for now for the beaches and headlands. We
will also see some east wind through The Gorge due to the easterly
gradient induced by the associated surface low out between 130w and
140w. The east winds will be strongest today, but linger for a couple
of days.

The next cold front approaches the coast Wednesday night and moves
through the forecast area midday on Thanksgiving. Snow levels will
remain high initially with this system. The front will move east of
the Cascades later in the day on Thanksgiving. There will be a fair
amount of showers in onshore flow behind the front Thursday night
with snow levels lowering to near Cascade Pass elevations overnight,
and the greatest coverage and intensity over the Cascades and the
coastal mountains. The models indicate that showers will continue
into Friday, but there could be some drying in the south part of the
area, from about Salem southward, by afternoon.

Rainfall totals through Friday could reach 3-6 inches in the Cascades
and in the coastal mountains (heaviest amounts in the north), with
0.5-1.5 inches in the valleys. Tolleson

Long term...Friday night through Tuesday...the models say the next
system spreads in with more rain Saturday as snow levels rising well
above the Cascade passes. Snow levels drop back near the passes in
showers behind the front on Sunday. A cool system moves through
Sunday night and Monday with more rain and mountain snow, followed by
decreasing precipitation on Tuesday. Basically the unsettled weather
pattern will continue. Tolleson

Aviation...warm front has lifted north of the area, ramping up
southerly winds along the coast. Rain picking up along the north
Oregon coast as well has lowered vis to IFR. Timing of the front has
sped up a bit from previous forecast. Expect deteriorating conditions
down at onp as well over the next couple hours. As the rain pushes
inland this evening, will see cigs and/or vis lower to predominantly
MVFR at inland terminals. This will persist through tonight until the
front crosses the area by Wednesday morning. Behind the front, expect
improving conditions as the more unstable airmass starts to lift the
cloud cigs and improve visibility.

Kpdx and approaches...VFR conditions this afternoon. As front
approaches this evening, expect cigs and vis to lower to MVFR around
01z. Could see occasional drops to IFR. Cigs and vis should start to
improve around 07-10z as the front moves off to the east. May still
see a mix of VFR and MVFR cigs until around 15z Wednesday morning.

Marine...southerly gales are going strong over the waters this
afternoon, with building seas. Winds should back off as late this
evening as this shortwave slides off to the north. Behind this
system, winds remain out of the south, but ease to 25 to 30 kt.
Another shortwave will skirt the waters Wednesday night into
Thursday, which will bring another round of southerly gales. A third
shortwave will turn winds southwesterly and bring another chance for
gale force winds Thursday evening. Shortwave ridging will bring a bit
of a break in the weather on Friday before another, possibly stronger
system, on Saturday.

Seas, already up into the low teens will build up into the
mid-to-upper teens this evening with the strong southerly winds.
Though seas will subside some later tonight, seas will stay in the
low-to-mid teens through Thursday. Seas start to subside on Friday,
possibly dropping below 10 ft by Friday evening. Expect seas to build
back up with the system over the weekend. -McCoy

Pqr watches/warnings/advisories...
Pz...Gale Warning until midnight PST tonight for coastal waters from
Cape Shoalwater Washington to Florence or out 60 nm.

Small Craft Advisory for rough Columbia River bar until 8 PM
PST this evening.

Small Craft Advisory for rough Columbia River bar from 4 am to
10 am PST Wednesday.



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