Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 220516
AFDPQR

Area Forecast Discussion
National Weather Service Portland Oregon
916 PM PST Sat Jan 21 2017

.SYNOPSIS...One final band of organized showers was moving north
across SW Washington this evening, and is expected to depart our
forecast area by around midnight. Meanwhile, a rapidly strengthening
low is developing just offshore from the OR/CA border. This system is
expected to linger off the Pac NW coast through early Monday before
moving south and weakening off the California coast Tuesday. The low
will spread a band of rain north across the forecast area early
Sunday, with showers, blustery winds, and possibly a couple
thunderstorms lingering through Monday. A high pressure ridge is then
expected to allow drier weather to develop for the rest of next week,
though a couple weak disturbances moving into the ridge may bring
some clouds and a slight chance of showers from time to time.

&&

.SHORT TERM...Tonight through Tuesday...Infrared and water vapor
satellite imagery show an impressive and rapidly developing low
pressure system roughly 200 miles west of Crescent City, CA. This
system is curling northward, which is a good thing, since the central
pressure of the low is near 980 mb and rapidly falling. A strong jet
max is pushing into this system, which is aiding in its development.
However, this same jet max is already shoving a dry slot toward the
southern Oregon coast. As a result, any warm frontal band of
precipitation lifting north through the area Sunday morning will
probably be fairly brief...only lasting 2-3 hours or so. This idea is
supported by the latest runs of the HRRR and UW WRF. The front will
also be in the process of occluding while it moves N-NE through
western Oregon and SW Washington. Behind this occluding front, models
suggest a decent surge of cold air aloft. This will enhance mixing,
which will probably result in some blustery conditions for most areas
Sunday...especially for the coast and higher terrain. Gusts 30-35 mph
will probably be common for most, but coastal and high elevation
spots could gust closer to 50 mph.

Temperatures continue to hover near freezing in the Hood River
Valley. Expect some ramp-up in easterly gradients as the low develops
offshore and the frontal band approaches from the SW, which should
help establish enough cold air for precipitation to be primarily snow
Cascade Locks eastward...but it will be close. This may be one of
those events where accumulating snow generally stays off the Gorge
floor west of Hood River, but only a couple hundred feet of elevation
are needed for more significant accumulations. Thus the Winter
Weather Advisory appears to be in decent shape for Sunday. However,
the bulk of the precipitation appears to be done for this evening, so
will cancel the advisory for the Upper Hood River for much of
tonight...starting it back up at 3 AM along with the rest of our
Gorge zones.  Weagle

Previous discussion from 236 PM Sat Jan 21 below...

A weakening surface low off the Washington coast will continue moving
north this afternoon and evening away from our forecast area. Showers
associated with the last part of this system will finish moving
through southwest Washington and northwest Oregon this afternoon and
evening. With relatively light easterly flow through the Gorge, snow
levels have lifted and have thus ended the snow advisory for the
Gorge for the remainder of today and this evening. We are see some
snow across the Cascade passes, and 2 to 4 inches is likely to fall
before it is is finished. Have left the snow advisory in effect for
the Upper Hood River Valley as snow is still possible in the higher
elevations of that forecast zone.

Precipitation eases for a while during the middle of tonight, then
increases again from the southwest later tonight and Sunday morning
as the next developing low out near 40N/137W this morning deepens to
around 960 mb along 130W near buoy 5 late tonight and Sunday. As this
deep low sets up off the coast late tonight, easterly pressure
gradients increase dramatically later tonight and Sunday morning and
this will likely help drive snow levels in the Gorge and the Upper
Hood River Valley closer to the surface. This low also spreads
another frontal band onshore from the southwest later tonight and
Sunday morning. Precipitation amounts look a little more broken up as
this band moves through compared to today, though we may get low end
advisory type snow in the Gorge and the Upper Hood River Valley again
and will continue the winter weather advisory for late tonight and
Sunday for these areas. The precipitation turns to showers and
decreases Sunday afternoon as the low remains off the coast,
maintaining the easterly offshore flow and suppressing any showery
onshore flow.

The low remains off the coast into Sunday night, then drops south to
off California later Monday and Monday night. This will cause showers
to decrease from the north Monday with some breaks in the clouds
likely to develop during the day.

The northerly flow aloft on the front side of a building eastern
Pacific upper ridge spreads onshore Monday night and Tuesday. The
models show a weak shearing disturbance moving through the forecast
area on Tuesday. The GFS model has been rather persistent in recent
days forecasting some spotty light precipitation over our forecast
area Tuesday. The NAM model now extends that far out and has some but
less precipitation than the GFS. The ECMWF and GEM models are dry.
Will stay dry for now but with a fair amount of clouds for now.
Tolleson

.LONG TERM...Tuesday night through Saturday...Large upper-level ridge
moving into the area will be the major player in bringing us a nice
break in the stormy weather we have been seeing over the past several
weeks. Can`t rule out a few stray showers on Wednesday as a shortwave
drops down along the leading edge of the ridge, but for the most
part, midweek should be dry.  Could see some fog develop Tuesday
night into Wednesday morning if the shortwave doesn`t bring more
clouds than currently forecast. Beyond Wednesday, east winds develop
across the area. Ridging looks to sit over the West Coast into next
weekend, keeping dry conditions, and light east winds could keep us
clear of any fog as well. Looks like next weekend could be a great
time to get outside if the current forecast holds true. -McCoy
&&

.AVIATION...Mainly VFR conditions this evening with the bulk of
the steady rain having passed through and now north of the local
area. The next round of steadier rain arrives starting south
around 09Z and moving north through about 12Z with a chance of
MVFR conditions. Gusty south winds develop along the coast after
09Z and into the valley starting after 12Z.

PDX AND APPROACHES...VFR conditions into the overnight, but next
round of steadier rain may bring MVFR cigs/vsbys again after 12z
along with gusty east wind. Bowen/Cullen

&&

.MARINE...Winds continue to gust out of the south to about 25 kt
this evening but will increase early Sunday as a strong surface
low moves north and eventually stalls off the Oregon coast. Gales
appear likely for most of the day Sunday across much of the
waters, and the Gale Warning remains in effect for Sunday. Given
the southeasterly component of the wind, not sure if the inner
waters will be as consistent with the stronger winds, but gales
likely to occur at least beyond about 5 nm from shore, especially
once winds turn more true southerly Sunday morning. Seas have
gradually subsided to 17 to 19 feet and will continue to drop
tonight before building again a bit on Sunday afternoon in
response to strengthening winds. Seas then ease to 15 feet or so
by early Monday morning. Expect more benign marine conditions
across the waters for most of next week. Bowen/Cullen

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...High Surf Advisory until 10 PM PST this evening for Central
     Oregon Coast-North Oregon Coast.

     Winter Weather Advisory from 3 AM to 6 PM PST Sunday for
     Central Columbia River Gorge-Western Columbia River Gorge-
     Upper Hood River Valley.

WA...High Surf Advisory until 10 PM PST this evening for South
     Washington Coast.

     Winter Weather Advisory from 3 AM to 6 PM PST Sunday for
     Central Columbia River Gorge-Western Columbia River Gorge.

PZ...Small Craft Advisory for Rough Columbia River Bar until 6 AM
     PST Monday.

     Small Craft Advisory for winds until midnight PST tonight for
     Coastal Waters from Cape Shoalwater WA to Florence OR out
     60 nm.

     Gale Warning from midnight tonight to 10 PM PST Sunday for
     Coastal Waters from Cape Shoalwater WA to Florence OR out
     60 nm.

     Small Craft Advisory for hazardous seas until midnight PST
     tonight for Coastal Waters from Cape Shoalwater WA to
     Florence OR out 60 nm.

&&

$$

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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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