Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 251127
Area Forecast Discussion
National Weather Service Portland OR
327 AM PST Sat Feb 25 2017
.SYNOPSIS...An upper ridge will move 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...The low that brought rain and
snow showers to the area on Friday has moved south, well offshore of
the Oregon/California border, and showers have dramatically decreased
over NW Oregon and SW Washington early this morning. Water vapor
imagery shows an upper ridge over Washington state moving south, and
beginning to move over extreme north Oregon. As a result, light east
winds and clearing skies are being observed along the north Oregon
coast. This clearing will spread south across the region this
morning. Lingering moisture combined with the clearing will result in
radiation cooling and possibly valley fog near sunrise this morning.
Any fog should be shallow and quickly clear later this morning for a
mostly sunny, but chilly afternoon.
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.
.AVIATION...Will see gradual clearing overnight, but have not
seen as much so far as expected. However, there is plenty of
moisture, so any break in clouds will likely allow IFR vis and/or
cig to form. With little to no wind and poor mixing, any fog
will persist well into Sat am, possibly as long as 20z. The
exceptions will likely be the coast and in the immediate vicinity
of the western mouth of the Columbia River Gorge, where light
offshore flow should keep VFR conditions in place.
KPDX AND APPROACHES...Expect IFR conditions to reform and last
through much of the morning hours. Then improvement to VFR by
Saturday afternoon. Bowen
.MARINE...Light offshore flow with seas 5 to 7 ft early this
morning will persist through most of Saturday. Next low pressure
system from the Gulf of Alaska will arrive Sat night 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. Bowen
OR...Winter Weather Advisory from 1 AM to 4 PM PST Sunday for Coast
Range of Northwest Oregon-Northern Oregon Cascade
Foothills-Northern Oregon Cascades.
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 4 PM PST Sunday for South
Washington Cascade Foothills-South Washington Cascades-
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
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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.