Area Forecast Discussion
Issued by NWS Portland, OR

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000
FXUS66 KPQR 252310
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
310 PM PST Sun Feb 26 2017

.SYNOPSIS...A northerly flow aloft into the Pacific NW through the
early part of the coming week will bring a couple of shortwaves
through for a continuation of cool weather with low snow levels and
chances for showers. By midweek weak high pres ridging will push
most precipitation chances north into WA, with temperatures
moderating some. A cold front late in the week is expected to bring
another round of rain and mountain snow back to the region.
&&

.SHORT TERM...Tonight through Tuesday...A northerly flow aloft over
the Pacific NW is expected to continue into Tue, with a couple more
shortwaves moving down the coast. This will keep the region in a
cooler than normal pattern, with snow levels generally down into the
Coast Range and lower Foothills. The first of the shortwaves coming
down late tonight and Sunday moves through by Sunday evening. Good
dynamic lift expected with this system, and is accompanied by fairly
deep moisture, so pops will be categorical. With dynamics, moisture
and favorable wind direction for orographic lift, expect the Coast
Range, Cascades and Foothills to see solid snow advisory amounts
despite the quick moving nature of the shortwave. At lower
elevations, models suggesting the snow level sets up somewhere
around 1000 feet, lowest in the north. Given the mild temperatures
today and appearance that clouds may flatten out and spread this
evening, there is some question as to whether snow levels will get
quite as low as promised, although dynamics may tend to help lower
snow levels. For now, will put a mention for some light
accumulations in the lower northern zones above 1000 feet late
tonight and Sunday, but hold off on any headlines due to the small
areal coverage of terrain above 1000 feet.

The showers will drop off with the passage of the shortwave in the
latter half of Sunday, but as the low level flow settles in out of
the nw Sun night and low levels remain moist, it will be difficult
to shut off showers completely, especially for the orographically
favored OR Cascades and Coast Range. The second shortwave come
through late Mon. This system will be similarly cold, but likely not
as strong and not with the same deep moisture, so pops will not be
quite as high. This could also result in some snow flakes being seen
at lower elevations, but snow accumulations will again be limited
more to the mountains, and should be lighter than the Sunday system.

A weak onshore flow conitnues behind the second trough Mon night
into Tue, but with air mass likely beginning to modify slightly as
upper heights begin to come up. Will show a diminishing trend in
pops in this time period, but still keep chance pops going into Tue.
Snow levels likely to rise slowly, more into the range of 1500 feet.

.LONG TERM...Tuesday night through Saturday...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...Widespread VFR conditions continue through this
evening with weak high pres over the region. A surface low
dropping south out of British Columbia will move along the coast
Sunday. Expect the associated rain shield to move in from the NW
after midnight, then slowly spread through the fcst area during
the morning hrs. Think MVFR conditions will develop from north to
south starting around KAST between 06Z-09Z, reaching KONP and
KEUG between 15Z-18Z. Cannot rule out some snowflakes mixing in
with the rain to start the day, but think that surface temps will
be a bit too warm. Rain tapers to showers from north to south
during the late morning and early afternoon hrs, with conditions
generally improving to VFR. Occasional MVFR still possible
through the afternoon in heavier showers.


KPDX AND APPROACHES...VFR conditions continue through most of
tonight. Rain will increase after 12Z, with MVFR cigs likely
developing by around 15Z. Rain tapers to showers by early
afternoon, with conditions returning to mainly VFR with
occasional MVFR in heavier showers. Pyle

&&

.MARINE...Weak high pressure is over the waters today, resulting
in a period of rather benign conditions. However, a surface low
pres system will dive south from British Columbia tonight and
move along the Washington and north Oregon coast Sunday and
Sunday night. Southwesterly winds will pick later this evening
and overnight, becoming 15 to 20 kt with gusts 25 to 30 kt. Winds
will turn to the northwest Sunday morning, and will continue to
gust to 25 kt at times through Sunday afternoon. Northwest winds
will continue Mon and may remain near low-end small craft
advisory thresholds through much of the day. Weak high pres will
build over the NE Pac for a good portion of next week, keeping
conditions rather quiet from Tue through Thu. The next front is
currently modeled to arrive late Thu or Fri. It looks fairly
strong at this point, bringing a good chance for gales.

Seas are running in the 5 to 7 ft range this afternoon. They will
be increasing overnight as a long period westerly swell arrives.
There will also be some wind waves and fresh swell generated by
the incoming low pressure system. Expect combined seas to build
into the low teens late tonight and remain at or above 10 ft
through at least Sunday night. Seas will gradually subside early
next week, then remain 10 ft through most of the week. Pyle

&&

.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.

     Small Craft Advisory for Rough Columbia River Bar from 2 AM to
     7 AM PST Sunday.
&&
$$

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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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