Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 290332
Area Forecast Discussion
National Weather Service Portland Oregon
830 PM PDT Wed Sep 28 2016
.SYNOPSIS...The region remains between weather systems with another
dry and mostly sunny day expected on Thursday. A low pressure system
will set up off well the coast late Thursday, approach the coast
Friday, and spread onshore this weekend. This system will bring an
increase in clouds, cooler temperatures, and increasing showers
beginning late Friday and last into the weekend. There will also be
some light snow in the higher Cascades this weekend.
.SHORT TERM...(Tonight through Saturday)...It was a very pleasant day
across the region today with sunny and dry conditions. Not much
change in the weather pattern through Thursday. In fact, a
persistent forecast for Thursday looks reasonable.Expect a repeat
of fog and low clouds along the coast later tonight into Thursday
morning. Will likely see some clouds along the Cascade foothills
Thursday morning as well. The moisture is very shallow, so clouds
that do form will be quick to burn off, leading to plenty of
sunshine on Thursday.
A low pressure system out near 50N/135W will drop southward on
Thursday, but remain well off the OR/WA coast and not effect the
weather in our area until Fri afternoon. The one exception is a
slight chance of a shower or a thunderstorm near the Cascade crest
late Thursday or Thursday night.
The low pressure system will move closer to the coast on Friday and
spread showers into the coastal region Friday afternoon/evening.
There may be a few showers over the higher Cascades Friday afternoon
as well. The valleys will likely stay dry through most of Friday,
with only some patchy morning fog or low clouds.
The low slowly spreads onshore Friday night and Saturday with a
decent short wave associated with the main low center rotating
onshore through the base of the low late Friday night and Saturday.
This should increase the showers by Saturday. Snow levels drop
dramatically in the Cascades Friday night and Saturday, possibly as
low as about 5000 feet.
A second drops south in the wake of the first low and moves into
southern Oregon and northern California Sunday. While this main
energy goes south of our area, we should still see a fair number of
showers in our forecast area Sunday, with greater coverage south than
.LONG TERM...(Saturday night through Wednesday)...No changes. Model
guidance continues to struggle a bit through the extended period
with the precise evolution of the upper trough that is moving across
the region. Latest trends suggest the trough may end up tracking a
bit more south and west, though the ECMWF continues to depict more
moisture than the latest, drier GFS solution. As a result, decreased
PoPs a bit on Sunday for many portions - particularly across the
northern and western portions of the forecast area - but still
maintained widespread chance PoPs across the area. Models diverge in
the timing of a pair of disturbances that may bring a couple of
rounds of lighter precipitation early next week, so have maintained
a generalized chance of showers for the end of the period. Snow
levels look to remain below 6000 feet for the start of next week,
but gradually rising to near 7000 feet by midweek. Meanwhile,
temperatures will gradually warm a few degrees early next week, but
still remain below normals. Cullen &&
.AVIATION...VFR continues this evening across most of the region,
with the primary exception being local IFR conditions along the
central Oregon coast in fog/low stratus. With shallow marine
inversion, expect a return to more widespread IFR conditions along
the immediate coastal areas to increase after 06z in the south,
but closer to 12z for the north coast. Expect VFR overnight for
much of interior, though local fog or low stratus may develop
after 13z. Confidence is highest towards the Cascade foothills,
and there remains around a 20 percent chance or less for
restrictions to develop at any of the interior TAF sites.
KPDX AND APPROACHES...VFR conditions through at least 13z. Expect
some patchy stratus to develop around the area, but only about 15
percent chance of impacting terminal between 13z-17z. After 17z,
VFR conditions under clear skies with light northwest surface
.MARINE...Seas have continued to gradually subside this evening.
While conditions remain rather steep with short wave periods,
heights have dropped enough to bring conditions below criteria, so
the advisory for hazardous seas will expire at 9 PM as planned.
Meanwhile, low-end advisory strength winds do persist over the
outer waters, and the advisory for winds will continue through 6
AM. May see a few localized advisory strength gusts a bit closer
to shore between Newport and Florence through around midnight, but
these will not be sufficiently widespread or frequent to warrant
an advisory for the inner waters.
An area of weak surface low pressure will move into the northeast
Pacific beginning late Friday with winds shifting to the south. and
coastal clouds increasing. Models are in better agreement that a
weak to moderate low pressure system will move into the coastal
waters around Monday. Cullen
PZ...Small Craft Advisory for winds until 6 AM PDT Thursday for
Waters from Cape Shoalwater WA to Florence OR from 10 to
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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.