Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 231105
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
305 AM PST Thu Feb 23 2017

.SYNOPSIS...A series of cool storm systems will bring cooler than
average temperatures, off and on showers and occasional snow to the
Coast Range and Cascade foothills through Friday night. The best
chance for snow to dip to sea level and the valley floors will be
Friday morning, but any low-elevation accumulations should be brief
and localized. A brief ridge will result in drier weather Friday
night and Saturday, but offshore winds will maintain cool
temperatures. A couple of cool storm system will return showers with
low snow levels Saturday night through Tuesday.

&&

.SHORT TERM...Today through Sunday...Temperatures this morning are in
the low to mid 30s early this morning. Fog is beginning to form in
the interior valleys and the visibility may be quite poor (~1/2 mi or
less) for many commuters this morning.

A shortwave trough will move over SW Washington and NW Oregon today
for continued showers. The showers are mostly offshore and along the
coast early this morning, but will increase inland this afternoon as
surface heating increases lift.  Snow levels will remain low, around
1000 to 1500 feet, but heavier showers could result in snow below
1000 feet at times. Like yesterday, snow, graupel, and small hail
will likely accompany the stronger showers and be possible at any
location regardless of elevation. Any lower elevation snow
accumulations will be brief, light, and localized, and generally less
than an inch.

Showers will wane this evening inland again due to the loss of
surface heating, but likely continue along the coast through the
night. This will once again prime the interior valleys for fog to
form late tonight or early Friday morning.

Another upper shortwave dropping south from near the Gulf of Alaska
will approach the Pacific NW tonight and bring another round of
showers for Friday. Models continue to show that the low will remain
100 to 150 miles offshore as it moves by the Oregon coast. This
should keep most of the moisture offshore and along the coast, but
added lift due to diffluence aloft will result in slightly more
showers Friday morning into the early afternoon. Therefore expect
another cool and showery day with the threat for low snow levels. The
coast range and Cascades could get 1 to 2 inches of snow on Friday
near and above 500 feet. Heavier showers will likely result in snow
below 500 feet, with possibly localized snow accumulations up to an
inch.

The upper shortwave will move south of Oregon Friday night and an
upper level ridge begins to slide over the area for offshore winds
and drier conditions Friday night and Saturday.

Another upper shortwave, similar to the others will then slide south
from the B.C. Coast and bring a return of cool and showery weather
Saturday night and Sunday. Snow levels will again be low between 1000
and 1500 feet with brief snow possible down to the valley floor.
Models hint that there could be more moisture with this system, and
the coast range and Cascades may see 2 to 4 inches of snow with
locally higher amounts. ~TJ

.LONG TERM...Sunday night through Thursday...The Pacific NW will be
between a broad upper level trough over most of the U.S. and an
Upper ridge over the NE Pacific. The trough will be more influential
to the local weather Sunday night through Tuesday with embedded
shortwaves bringing periods of rain and snow showers. The snow levels
will remain low through Monday, then begin to rise Tuesday. The upper
level ridge then moves over the area Tuesday night and Wednesday
holding through late in the week for drier and warmer weather. ~TJ

&&

.AVIATION...Fog is taking a bit longer to form this morning as
the upper clouds have been slower to clear. In areas where skies
have scattered out (KHIO & KSPB) fog has started to form and
became quite thick quickly. Confidence is still high that most
TAF sites will see dense fog this morning, but due to later
onset, timing has been pushed back a bit. Fog began in Eugene but
has recently lifted to a broken stratus deck. Current thinking is
that low stratus will be preferred at KEUG over dense fog.

KPDX AND APPROACHES...Skies have been slow to clear, but once the
3-4 kft deck scatters out, expect fog to develop and spread
quickly. /Bentley

&&

.MARINE...Benign marine weather for for the next week with seas 5
to 8 feet and winds remaining below small craft advisory
criteria. There is a chance winds could briefly gust to small
craft strength Friday afternoon/overnight, but expect winds to
remain below small craft strength. There will be other similar
instances Sunday through Tuesday, but in each of these cases it
appears borderline and brief windows of stronger winds. While it
is possible we may need to issue a small craft advisory at some
point during this period, at this time do not anticipate one
being issued. /Bentley

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.
&&
$$

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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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