Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 251717
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
918 AM PST Sat Feb 25 2017

.SYNOPSIS...An upper ridge will move from north to south across the
area today for a brief break in rain and some sunshine. A low will
then approach from the north this evening. A cold front will produce
rain and mountain snow late tonight through Sunday. Snow levels will
be around 1500 feet so the coast range and Cascade foothills should
have accumulating snow. A couple of weak lows will continue showers
Sunday night through Wednesday.

&&

.SHORT TERM...Today through Tuesday...An east west oriented ridge of
hgh pres was seen in water vapor pictures shifting south along the
WA coast this morning, between two shortwave troughs in a northerly
flow. A high stratocumulus deck seen over the interior of sw WA
extending south down to around Mt Hood was indicative of some
residual low level moisture that may wind up resulting in some
cumulus today. Otherwise there were also some areas of low clouds
and fog mainly in the interior valleys that was generally pretty
fragmented, and should break up by afternoon.

Remainder of short term discussion unchanged...Another upper level
shortwave and associated surface low will drop down from the B.C.
coast tonight and produce another round of rain and snow for SW
Washington and NW Oregon. Precipitation will spread from north to
south with a cold front late tonight through Sunday afternoon. Snow
levels will be between 1000 and 1500 feet, but would not be
surprised if snow occasionally mixes down to elevations slightly
below 1000 feet. Modeled 850mb temperatures are a couple degrees
warmer than it was for the last few lows, and do not think there
will be snow down to near the valley floors. Expect the coast range,
and the Cascade foothills to get 3 to 5 inches of snow from late
tonight through Sunday afternoon, with 4 to 8 inches for the
Cascades, and have issued winter weather advisories for these
locations. The interior valleys can expect 0.25 to 0.5 inch of rain,
and 0.5 to 0.75 inch of rain is possible for the coast.

Rain and snow showers behind the front will persist Sunday night and
Monday as the low moves inland across NW Oregon, with little change
to the snow levels. A weak upper level trough will slide north to
south Monday night and Tuesday for continued showers and seasonally
cool weather. ~TJ

.LONG TERM...Tuesday night through Friday...Showers will decrease
south of Salem Tuesday night and Wednesday as high pressure begins to
build over the area and moves the storm track further north. Showers
will likely continue across extreme north Oregon and SW Washington.
The upper ridge will intensify Wednesday night as a low over the Gulf
of Alaska digs south into the NE Pacific for a brief break in
precipitation Wednesday night and Thursday. A warm front will bring
rain to extreme NW Oregon and SW Washington Thursday night before a
cold front produces more widespread precipitation  Friday. Snow
levels are expected to rise to around 3500 to 4000 feet by Friday.
~TJ

&&

.AVIATION...With weak high pres and light winds over the region
this morning, IFR fog and low stratus has formed over most of the
lowlands. The exceptions are at KONP at KTTD, where light
offshore flow has kept conditions clear. The low cloud layer is
very thin and should burn off fairly quickly later this morning.
Then expect VFR conditions this afternoon and evening. Another
low pres system approaching from the north with bring increasing
rain and likely MVFR conditions overnight into Sun morning.

KPDX AND APPROACHES...Expect IFR stratus to burn off between
18Z-19Z. Then VFR conditions prevail this afternoon and evening.
Rain and MVFR cigs spread back in overnight into Sun morning.
Pyle

&&

.MARINE...Light offshore flow with seas 5 to 7 ft early this
morning will persist through most of today. Next low pressure
system from the Gulf of Alaska will arrive tonight into Sun as a
surface low tracks south down the Pacific NW shoreline. Will see
winds increase over the waters as the low tracks along the
coastline. Have issued Small Craft Advisories for Winds and Seas
as swell will also increase behind the low.

Beyond Sunday, a lack of organized surface low pressure centers
will limit chances for small craft strength winds until much later
in the week. Seas will follow this same pattern, approaching
near 10 feet on Sunday/Sunday night and again later in the week
ahead of the next front. Pyle/Bowen

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 1 AM to 7 PM PST Sunday for
     Northern Oregon Cascades.

     Winter Weather Advisory from 1 AM to 4 PM PST Sunday for Coast
     Range of Northwest Oregon-Northern Oregon Cascade
     Foothills.

     Winter Weather Advisory from 4 AM to 7 PM PST Sunday for
     Cascade Foothills in Lane County-Cascades in Lane County-
     Central Coast Range of Western Oregon.

WA...Winter Weather Advisory from 1 AM to 7 PM PST Sunday for South
     Washington Cascades.

     Winter Weather Advisory from 1 AM to 4 PM PST Sunday for South
     Washington Cascade Foothills-Willapa Hills.

PZ...Small Craft Advisory for winds from 10 PM this evening to 4 PM
     PST Sunday for Coastal Waters from Cape Shoalwater WA to
     Cascade Head OR out 60 nm.

     Small Craft Advisory for hazardous seas from 4 AM Sunday to 4
     AM PST Monday for Coastal Waters from Cape Shoalwater WA
     to Florence OR out 60 nm.

     Small Craft Advisory for winds from 1 AM to 4 PM PST Sunday 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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