Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 202348
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
348 PM PST Mon Feb 20 2017

.SYNOPSIS... Another moderately strong low is forecast to
move onshore and across west central Oregon Tuesday. Gusty winds
should be confined closer to the central Cascades. Also expect
another decent dose of mountain snow. Colder air associated with
the parent upper trough will sag into the forecast area starting
tomorrow night and gradually lower snow levels through the weekend.
Precipitation amounts will remain relatively light but could mix in
snowflakes to sea level under the showers.
&&

.SHORT TERM...Tonight through Wednesday Night...PLenty of mountain
showers have trailed in the wake of this morining`s low. Pretty
optimal SW flow will continue for a few more hours across the South
Washington Cascades and have extended the advisory up there through
7 pm. Otherwise, most of the area will stay in a relative lull ahead
of the next low with it`s primary precipitation arriving over Lane
county around mid-evening. This low will likely have weaker winds
overall, but should at least focus any gusty winds to the higher
terrain south of Mt. Jefferson tomorrow mid-morning. Snow levels
will be a little lower but precipitation amounts are looking
slightly more spread out in time than today. As such, the Cascades
will be on the cusp of needing another Snow Advisory and this time
to include the Central Cascades as well. Today`s moderate rains may
push select river points back to flood stage. The Tualatin at
Farmington is garnering the most interest with potential to rise
above flood stage tomorrow mid-morning. Upstream reservoir activity
may diminish the threat, however. This interest is followed by the
Pudding currently forecasted to flood Wednesday and the Marys
rivers not forecasted to flood but rise well into action stage.

The snow levels will lower as the colder air moves overhead as the
larger parent upper trough then shifts southeast Tuesday Night. By
then, showers will begin to dominate and the air mass becomes a
little drier. There will be plenty of showers to bring continued
light accumulations to the Cascades/Cascade Foothills above 1500
feet plus the higher Coast Range highway passes through Wednesday
night. THe atmosphere will also be modestly unstable and there could
be the occasional thunderstorm. Don`t have a lot of confidence just
yet to include them, but did have enough to expect the occasional
heavier shower which could be the first day to mix in some non-
accumulating snowflakes down closer to sea level. /JBonk


.LONG TERM...Wednesday Night through Monday...The cold upper low
will continue funneling colder modified arctic air from the Pacific
and then over the Pacific Northwest. Most days will see some threat
of shower activity with perhaps Saturday Afternoon and Night as the
most likely to stay dry. Outside of that period, there will be
plenty of shower activity and low snow levels through the extended.
Fortunately, moisture will remain rather limited for each day and
that should limit any threat of major storms. However, elevations
above 1,500 feet and the Gorge/Hood River Valley could pick up an
inch or two each day. Elsewhere, fully expect there will be times
where snow may fall down to sea level, but do not expect
accumulations to persist below 1,000 feet for more than a couple
hours at a stretch. Even then, it will take a rather robust shower
to bring any accumulating snow down to sea level. /JBonk

&&

.AVIATION...Showers mostly relegated to the terrain this
afternoon and will taper off through the evening. Even without
showers, CIGS across the valley and coast remain MVFR. Still
expect improvement to VFR conditions this evening and into the
overnight hours, but then MVFR CIGS are likely to return with
incoming steady rain spreading from south to north starting
around 08Z. Tuesday is looking like a near repeat of today with
breezy conditions (less than today) developing south during the
late morning and afternoon hours and steady rain turning to
showers by afternoon.

KPDX AND APPROACHES...Likely to see continued VFR conditions
through much of the overnight but return to MVFR with CIGS around
2000 ft as steady rain returns after about 10Z. Bowen

&&

.MARINE...After today`s low, another low will take much the same
trajectory tonight and into Tuesday, coming onshore near the
central OR coast. Strongest winds will remain south of the local
waters, but will still likely see gusts to about 25 kt locally.
Seas are running 10 to 12 ft this afternoon but will drop this
evening to 7 to 9 ft and then further to 6 to 8 ft by Tuesday
morning. Could see a small increase with winds during the day
Tuesday, but expect seas to remain below 10 ft once they drop
this evening.

After Tuesday, the pattern calms down for a few days as a trough
settles over the WA/OR coastal waters with more benign winds and
seas through the remainder of the workweek. Bowen

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 4 PM PST this afternoon for
     Northern Oregon Cascades.

WA...Winter Weather Advisory until 4 PM PST this afternoon for South
     Washington Cascades.

PZ...Small Craft Advisory for winds from 7 AM to 4 PM PST Tuesday
     for Coastal Waters from Cape Shoalwater WA to Florence OR
     out 60 nm.

     Small Craft Advisory for hazardous seas until 4 PM PST this
     afternoon for Coastal Waters from Cape Shoalwater WA to
     Cascade Head OR out 60 nm.

     Small Craft Advisory for winds until 4 PM PST this afternoon
     for Coastal Waters from Cascade Head OR to Florence OR out
     60 nm.

     Small Craft Advisory for hazardous seas until 7 PM PST this
     evening for Coastal Waters from Cascade Head OR 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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