Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 261713
Area Forecast Discussion
National Weather Service Portland OR
913 AM PST Sun Feb 26 2017
.SYNOPSIS...North flow aloft will steer a couple of shortwaves
from north of the area to the Pacific NW today through Tuesday for
cool and showery weather. Building high pressure midweek will keep
precipitation chances north into Washington, and temperatures will
moderate some. A cold front on Friday will bring another round of
rain and Cascade snow with showers continuing through next weekend.
.SHORT TERM...Today through Tuesday night...Upper low was seen off
the south WA and north OR coast this morning in water vapor imagery
moving south. Surface low lagged a little, still off the north WA
coast at 16z this morning. Main band of stratiform precipitation had
pushed inland over the Coast and into the Willamette Valley as a
cold front was moving onto the coast, with more showery
precipitation behind the front. Have seen some accumulating snow in
ODOT cameras and spotter reports as low as 500 feet with the
heaviest precipitation, but temps down that low have not lingered
long below freezing, so the snowfall is expected to be short-lived.
General snow levels still look like they on the order of 1000 ft,
and the current set of winter weather advisories look on track. It
may be difficult to see the higher Cascades reaching advisory snow
amounts given the higher criteria, but with several inches of snow
likely still today will hang on to a low end advisory. Although
model soundings are not particularly favorable, with the upper low
dropping south off the coast will retain a slight chance for thunder
on the coast and over the coastal waters this afternoon. Inalnd
precipitation will transition to showers today as the cold front
continues to move inland.
Remainder of short term discussion unchanged...Showers will ease
late tonight, but moist onshore flow will maintain at least isolated
showers Monday morning.
Another shortwave trough will enhance showers Monday afternoon and
evening as it drops SSW across Washington and Oregon from the B.C.
coast. Snow levels will remain at or near 1200 feet, and the coast
range and Cascade foothills may see additional 1 to 4 inches of snow
Monday afternoon and night. Moist onshore flow will continue showers
over the area Tuesday, but rising snow levels should limit travel
impacts for the coast range and Cascade foothills.
Another shortwave approaches from the north Tuesday night but a
building upper level ridge over the NE Pacific may limit the southern
progression of this storm. Expect rain and mountain snow for extreme
SW Washington and NW Oregon with less of a chance for precipitation
across Lane County. ~TJ
.LONG TERM...No Changes. Previous discussion follows...Wednesday
through Saturday night...Models develop a rather flat upper level
ridge over the region midweek, tending to push the best chances for
precipitation up into WA. With the surface ridge setting up across
southern OR though, will need to keep some low pops down into NW OR
Wed and Thu due to weak but moist low level onshore flow and
isentropic lifting. Fri GFS GEM and EC all drive a cold front through
with a trough originating in the Gulf of Alaska. With good agreement
in models as well as strong dynamics and good moisture, will go with
likely pops as the front moves through. Post frontal showers continue
Sat as a broad upper trough over the NE Pacific spreads inland.
.AVIATION...Low pres dropping south along the coast is bringing a
front and associated rain shield through the region this morning.
This is resulting in widespread MVFR conditions. The front is
currently east of the Coast Range and will push into the Cascades
by midday. Rain will transition to showers behind the front, with
conditions generally improving to VFR. Occasional MVFR in heavier
showers will be possible through the afternoon.
KPDX AND APPROACHES...A front bringing steady rain and MVFR
conditions this morning. Expect the front to push through the
terminal by around 18Z. Rain transitions to showers behind the
front. Expect mainly VFR conditions this afternoon and tonight,
with occasional MVFR in heavier showers. Pyle
.MARINE...A surface low pressure system currently located along
the central WA coast will continue to move south today. It will
be along the north OR coast by the late afternoon and will
dissipate tonight. A cold front moved through the waters earlier
this morning, bringing SW winds gusting 25 to 30 kt. Winds have
now switched to the NW behind the front and subsided a bit.
Decided to drop the small craft advisory for winds for the
northern waters, but will hold onto the advisory for the central
OR waters where gusts to 25 kt may continue at times through the
Winds will drop below small craft advisory thresholds tonight.
Then expect persistent NW winds through the first half of next
week and weak high pres settles over the NE Pac. Winds may reach
low-end small craft advisory speeds at times. A fairly strong
front is expected late in the week, and will likely bring a
period of southerly gales.
Seas are a little slow coming up this morning, but a longer
period westerly swell is beginning to move into the waters.
Seas should build above 10 ft later this morning, then remain
at or just above 10 ft through much of Mon. Sea will subside
toward the middle of next week. Pyle
OR...Winter Weather Advisory until 7 PM PST this evening for Cascade
Foothills in Lane County-Cascades in Lane County-Central
Coast Range of Western Oregon-Northern Oregon Cascades.
Winter Weather Advisory until 4 PM PST this afternoon for Coast
Range of Northwest Oregon-Northern Oregon Cascade
WA...Winter Weather Advisory until 7 PM PST this evening for South
Winter Weather Advisory until 4 PM PST this afternoon for South
Washington Cascade Foothills-Willapa Hills.
PZ...Small Craft Advisory for hazardous seas until 10 AM PST Monday
for Coastal Waters from Cape Shoalwater WA to Florence 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
Small Craft Advisory for Rough Columbia River Bar from 3 PM
this afternoon to 8 PM PST this evening.
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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.