Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 272244

Area Forecast Discussion
National Weather Service Portland OR
244 PM PST Mon Feb 27 2017

.SYNOPSIS...A trough of low pres will swing across WA tonight
continuing cool showery weather. Flow will gradually change from
northerly to westerly Tue and Wed, keeping a chance for showers
going, but allowing temps to moderate a little. Late in the week a
couple of fronts will move through for more widespread precipitation

.SHORT TERM...Tonight through Thursday...Vort max seen in water
vapor pictures was moving down Vancouver Island, and expected to
swing across WA tonight. Radar showed fairly widespread showers
across the forecast area this afternoon in a westerly onshore flow,
with heaviest showers generally over the upslope terrain and some
evidence of rainshadowing in the Willamette Valley. Expect showers
to continue widespread through the evening as the shortwave moves
across. Although showers should decrease some behind the shortwave
later tonight, a nw onshore flow is expected to allow showers to
persist, but with more reliance on orographic lift. Snow level early
Mon afternoon had generally lifted into the Foothills and higher
Coast Range. Will continue with the winter weather advisory for the
Foorhills and higher Cascades through the evening.

Models continue to show the upper flow transitioning from northerly
to westerly Tue and Wed, as upstream shortwaves begin to dig out a
trough over the eastern Gulf of Alaska. This will bring allow air
mass to modify some, with snow levels creeping up over the next
couple of days. Main focus of moist onshore flow and precipitation
will tend to shift slowly north with the rising upper heights, but
qpf fields still suggest that pops are likely persist for much of
the area through Wed. Wed night and Thu morning looks like the best
chance for a dry period, particularly for the southern half of the
forecast area, as a very flat ridge reaches its peak. Models remain
in good agreement in showing a shortwave ejecting out of the ne
Pacific Thu afternoon, increasing the onshore flow and brushing at
least the northern part of the forecast area with a weak warm front.
This will bring better chances for rain to the region by Thu

.LONG TERM...Thursday night through Monday...Strong westerly
flow aloft gives way persists for much of the second half of the
week, until a broad upper trough pushes deeper into the Pacific
Northwest during the by the weekend, providing for continued
precipitation. Snow levels will fall down to around 2,000 feet on
Saturday behind the front, which supports snow showers down into the
higher Cascade foothill elevations. Models remain in fair agreement
that deeper moisture will enhance rainfall again early Sunday as
another shortwave embedded in the flow rotates around the upper
trough and pushes through the region. Model solutions diverge a bit
more significantly by early next week, but there remains at least
some agreement that another round of steady moisture may again
approach.   Cullen

.AVIATION...Continue to expect a mix of MVFR and VFR conditions
as showers move through the area due to a disturbance moving
through this afternoon and this evening, with much of the MVFR
conditions this afternoon in the northern valley areas such as
around KPDX. Conditions will probably not change much or settle
into MVFR tonight as the showers and onshore flow continue
tonight into Tuesday. May see conditions lift into VFR Tuesday
afternoon but there should still be some showers around as
onshore flow continues.

KPDX AND APPROACHES...Expect a mix of MVFR and VFR conditions
that will turn mostly to MVFR tonight into Tuesday morning,
possibly lifting to VFR cigs Tuesday afternoon. Showers will be
most numerous into this evening. Some showers will likely
continue through Tuesday. pt

.MARINE...Another disturbance was moving through the Pacific NW
this afternoon, and will sweep inland and east of the waters
tonight. This will continue the NW winds over the waters with
occasional gusts near 25 kt that will ease up late tonight and
Tuesday. The next disturbance moving through largely to our
north brings some more SW winds into the waters late Tuesday and
Tuesday night that will probably exceed Small Craft Advisory
thresholds in the northern waters. Those winds ease up on
Wednesday. The next batch of winds increase from the south on
Thursday and should be high end Small Craft Advisory winds or
possibly borderline gale force winds. Those winds turn westerly
and decrease Friday.

Seas remain 10-11 ft this afternoon, a bit above wave model
guidance. Seas are forecast to drop below 10 ft tonight, but
based on current trends, held onto the Small Craft Advisory for
seas into this evening. Seas rise up to just above 10 ft
Wednesday into early Thursday before subsiding again. The next
batch of seas above 10 ft is expected arrive Thursday night. pt

OR...Winter Weather Advisory until 10 PM PST this evening for
     Cascade Foothills in Lane County-Northern Oregon Cascade
     Foothills-Northern Oregon Cascades.

WA...Winter Weather Advisory until 10 PM PST this evening for South
     Washington Cascade Foothills-South Washington Cascades.

PZ...Small Craft Advisory for hazardous seas until 7 PM PST this
     evening for Coastal Waters from Cape Shoalwater WA to
     Florence OR out 60 nm.

     Small Craft Advisory for winds until 10 PM PST this evening for
     Waters from Cape Shoalwater WA to Florence OR from 10 to
     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 3 AM to
     8 AM PST Tuesday.

     Small Craft Advisory for Rough Columbia River Bar from 4 PM to
     9 PM PST Tuesday.


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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. is the U.S. government's official web portal to all federal, state and local government web resources and services.