Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 282203
Area Forecast Discussion
National Weather Service Portland Oregon
302 PM PDT Wed Sep 28 2016
.SYNOPSIS... The forecast area will be in between systems tonight and
Thursday for dry weather and not many clouds. A low pressure system
will set up off well the coast later Thursday, approach the coast
Friday, and spread onshore this weekend for an increase in clouds,
cooler temperatures, and increasing showers beginning later Friday,
with even some snow in the higher Cascades this weekend.
.SHORT TERM...(Tonight through Saturday)...We will be in between
systems tonight and Thursday for dry weather and a minimum of clouds.
What few clouds we had this morning have cleared this afternoon, and
temperatures this afternoon will be close to those of Tuesday.
Not much change in the pattern is expected tonight and most of
Thursday. Expect mostly a repeat of the fog and low cloud pattern on
Thursday morning as compared to this morning, with some fog and low
clouds along the coast, possibly some more along the Oregon Cascade
foothills, but only patchy fog or low clouds along the Interstate 5
corridor. We should see plenty of sunshine most areas on Thursday
with temps close to those today, perhaps down a degree or two.
A low pressure system out near 50N/135W this afternoon will be
dropping south off the coast during the day Thursday, but should
remain far enough offshore to not affect our forecast area much yet.
The one exception is a slight chance of a shower or a thunderstorm
near the Cascade crest late Thursday or Thursday night.
This low will be approaching closer to the coast on Friday, but it
looks like the showers probably will not spread onshore along the
coast and into the coastal mountains until Friday afternoon as the
main cooler air aloft and instability remain offshore. We may see a
few showers over the higher Cascades Friday afternoon as well. The
valleys until probably 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 representing 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)...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 will continue through the evening except near some
of the headlands and locally inland along the coast where some
fog and stratus is producing IFR conditions. The marine inversion
will remain very low with tops along the coast only around 1000 to
1500 feet. Thus, expect ifr and lifr cigs and visibility to
increase along the coast aft 07z. Inland will remain mostly vfr
but there could be some patchy fog or low stratus develop around
12z through 17z. The areas mostly likely to see fog and stratus
inland will be the Cascade foothills, much like today.
KPDX AND APPROACHES...vfr conditions through Thursday. 20% chance
of ifr stratus 12-15z. Schneider
.MARINE...High pressure currently over the northeast Pacific will
gradually weaken over the next couple of days, which will
gradually bring a decrease in the gusty northerly winds currently
blowing across the waters. seas running around 7 feet which is
mostly wind wave and short period fresh swell for choppy
conditions. The small craft advisory for wind over the outer
waters will continue but winds will diminish Thursday. As the
wind drops off the short period fresh swell will subside and sea
conditions will improve overnight.
An area of weak surface low pressure will move into the northeast
Pacific beginning late Friday with surface 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 northern models around Monday. Schneider
PZ...Small Craft Advisory for winds until 3 AM PDT Thursday for
Waters from Cape Shoalwater WA to Florence OR from 10 to
Small Craft Advisory for hazardous seas until 9 PM PDT this
evening 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.