074 
FXUS66 KPQR 122222
AFDPQR

Area Forecast Discussion 
National Weather Service Portland OR 
322 PM PDT Wed Apr 12 2017

.SYNOPSIS...A surface low currently located west of the central OR
coast is moving north through the offshore waters today. The low will
bring an occluded front through the region during the late afternoon
and early evening hours. A period of heavy showers and isolated
thunderstorms will accompany the front. Showers will become more
scattered later this evening behind the occluded frontal passage.
Snow levels will lower overnight and remain below the Cascade passes
Thursday and Friday as a cool upper trough moves over the area. Dry
weather is expected Saturday and early Sunday before the next system
arrives later Sun. The active weather pattern likely continues
through at least the first half of next week. 

&&

.SHORT TERM...Tonight through Saturday night...An occluding low pres
system is located about 220 mi west of Newport this afternoon and is
moving north through the offshore waters. The occluded front is very
well defined on satellite and is now within 100 mi of the coast.
Showers have begun to increase over the past couple hours ahead of
the front as surface temps over the interior lowlands have warmed to
around 60 deg F, increasing the low level instability. There have
also been a couple of lightning strikes detected near the Cascade
foothills in Linn and Marion counties. Expect showers will only
increase in coverage and intensity as the occluded front moves
onshore later this afternoon and taps into the low level instability.

The front will move into the Cascades by mid evening, then
east of the Cascades by late evening. Showers will continue but come
more scattered behind the frontal passage, but will continue through
the night. Snow levels have been around 6000 ft or above today, but
they will drop sharply later tonight as a colder air mass moves in
behind the front. Expect some light accumulations down to the passes
overnight, but amounts should remain safely below advisory criteria. 

The offshore surface low will remain west of the WA waters into Fri,
which will bring continued moist onshore flow. There will also be a
broad upper level trough over the NE Pac. These features will combine
to keep plenty of shower activity going over the Pac NW through the
end of the week. The best showers will be on Thu, as the cold pool
aloft will be located just to our north. Decided to add a slight
chance of thunder to the coastal waters and coast through Thu
morning, then extending into the interior during the afternoon. Snow
levels will be in the 3500 to 4000 ft range, so expect several inches
of snow at the Cascade pass levels and above. However, think road
temps will be warm enough to limit impacts to travel. With the low
snow levels, and heavier showers have the potential to bring small
hail down to the lower elevations. Upper level heights will be rising
and the NE Pac surface low will be weakening on Fri. There will still
be showers around, but they will be much weaker than those on Thu.
They will taper off rapidly Fri evening.

Sat looks likely to provide a welcome dry break. A weak upper level
ridge will move over the Pac NW. There will likely be some clouds
around to start the day, but most locations should see some sun in
the afternoon. High temps over the interior lowlands will likely
reach near 60 deg. Pyle

.LONG TERM...(Saturday night through Wednesday)...The shortwave upper
level ridge axis is modeled to move over the Pac NW Sat night. Expect
dry weather to last into Sun morning. Then the next low pres system
is modeled to push into N Calif and S Oregon during the day Sun.
Yesterday the fcst models were keeping the associated precip south of
our CWA, but today they have drifted further north. Have increased
PoPs across the region Sun afternoon and evening, especially over the
southern half of the CWA. However, precip looks to be light, and
temps should be a little warmer, into the low 60s for the lowlands.
The a broad upper level trough sets up over the NE Pac for the first
half of next week. This will continue the trend of mostly cloud, wet,
and cooler than average temps. Pyle


&&

.AVIATION...Mainly VFR conditions this afternoon with some
occasional MVFR still at the coast. Seeing some TS pop up this
afternoon and produce MVFR VIS with moderate to heavy rain. Will
continue to see a chance of TS until after sunset, particularly
inland from the coast. Otherwise VFR conditions with some gusty
winds this afternoon and again Thursday morning.

KPDX AND APPROACHES...VFR with showers. Slight chance of TS
through this evening. If TS does affect the terminal, expect
gusty outflow winds out of the W or SW and heavy rain. Otherwise,
moderate offshore flow with occasional gusts to around 20 kt.
Bowen

&&

.MARINE...Winds continuing to hover around 20 kt with broad low
pressure off the WA/OR/N CA coast. As low pressure moves north, 
remaining well offshore, it will maintain Small Craft Advisory 
winds over the local waters through at least Thursday and 
possibly into Friday. High pres finally builds over the waters 
Fri night and Sat, for decreasing winds. 

Seas running 8 to 9 ft this afternoon based on buoy observations
and expect them to remain in that range through Friday. Could see
a brief 10 ft observation sometime over the next couple of days,
but think seas will generally stay below that threshold. Then 
seas gradually diminish over the weekend, easing to around 5 to 6
ft by Sunday. Bowen

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds until 5 PM PDT Thursday for 
     Coastal Waters from Cape Shoalwater WA to Florence OR out 
     60 nm.

     Small Craft Advisory for hazardous seas until 6 PM PDT 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.