Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 242217

Area Forecast Discussion
National Weather Service Portland OR
317 PM PDT Sat Oct 24 2020

.SYNOPSIS...A few remaining showers but skies are beginning to clear.
High pressure over the Pacific expected through mid next week. Gusty
winds expected today through early Sunday morning bringing in ample
cool air from the Columbia Basin. Likely temperatures will be cooler
Sunday night before slowly warming on Monday through mid week.
Settled weather through Wednesday.


.SHORT TERM...Tonight through Tuesday...Satellite still shows the
remnants of the low that was moving southeast along the Oregon coast
this morning, although it is quickly moving out of the area. The
westerly flow associated with this passing system is beginning to
shift northeasterly along the north coast while the central coast
remains westerly. Some lingering showers are present this afternoon
especially around where the Willamette and the Columbia River
intersect. This likely is due to some meso-scale convergence of two
different air masses: easterly flow through the Gorge and more of a
northerly wind coming down from Washington. The jet stream aloft is
generally meridional with the area sitting in the right exit region
of the 130 mph jet streak. This jet will enhance the high pressure
that is building over the Pacific, and encourage a trough of cooler
air to push down from Canada along the northern Rockies.

This pattern of high pressure over the Pacific and a cool air digging
trough is commonly associated with strong easterly winds; while in
essence similar to the wind event that occurred in early Sept, it is
not going to be nearly as strong. Winds will likely be the most
intense this evening into tomorrow as the cool air reaches it`s
"peak" low temps. The easterly winds combined with the cool air
pooling in the Columbia Basin sets the area up for a few cold nights
tonight and Sunday. Sunday is expected to be the chilliest night due
to the stronger winds today which will help inhibit as much
radiational cooling. Still can expect surface temps just above
freezing tonight.

By Sunday, the winds will ease and conditions will be clear and dry.
Easterly winds will prevail through the northern portions of the
forecast area while through the southern Willamette Valley will
likely be more northerly. With clear skies and lighter winds, Sunday
night will be the coolest night of the weekend. Many areas below
2000 ft will see temperatures around 25-30F inland and 30-35F along
the coast. Being at the tail end of the growing season, decided to
issue a freeze watch for many interior locations. Clear skies and
quiet weather will persist through Tuesday.    -Muessle

.LONG TERM...Tuesday night through Friday...Towards the middle of the
week is when the forecast becomes a bit more fuzzy. Tuesday night
into Wednesday conditions will continue to be dry and generally
clear. By late Wednesday, some models are beginning to show the signs
of the ridge weakening and flatting out with a long-wave trough
advancing towards the area from the Gulf of Alaska. However, there is
quite a bit of model uncertainty at this time. Recent runs have shown
this system slowing and not really reaching the area until Thursday
night. With that said, there are discrepancies regarding both the
timing and the track of this trough. Decided to stay conservative
both with the onset and track of this system.    -Muessle


.AVIATION...Weak low pressure along the Oregon coast will push
further southward tonight, with building high pressure over
eastern Washington. Plenty of VFR clouds from the coast mtns
eastward across the Cascades and east slopes. As the offshore
flow increases, expect continued gradual decrease in these clouds
this afternoon through this evening.

With building high east of the Cascades, will have increasing
north to northeasterly winds across the area into tonight, and
continuing through Sunday. The strongest winds will be later
tonight into Sunday am, with east to northeast gusts 25 to 35 kt
over the higher terrain and coastal areas, but gusts 35 to 45 kt
likely in the western Columbia River Gorge, as well as near
passes of the Cascades. Inland areas to south and north of
Portland likely to have breezy winds, but think 10 to 20 kt at
most. No concerns for LLWS, as winds aloft stay east to
northeast. Just bumpy at times.

For detailed regional Pac NW weather information, go online to:

KPDX AND APPROACHES...Clouds over area will gradually break up
this afternoon into early evening, with scattered clouds by 01Z,
and clearing after 06Z. Offshore flow with east winds through
Sunday, though strongest winds expected from late this evening
through mid-morning Sunday, with gusts 30 kt at times. No LLWS
expected as winds aloft remain east to northeast. Just bumpy at
times.   -Rockey


.MARINE...Low pressure near Florence will continue drifting south
this evening. Building high pressure over the inland Pac NW will
bring increasing east to northeast winds to the coastal waters
this afternoon through Sunday. Should see gusts 25 to 30 kt at
times this afternoon through Sunday, with strongest winds likely
in areas downwind of the gaps in the coastal terrain. Will
maintain current Small Craft Advisory. Winds will ease later
Sunday as offshore pressure gradients start relaxing. By Monday,
northerly flow develops as high pressure over the NE Pacific
nudges closer and the inland Pac NW high shifts farther away.
From mid week onward the high pressure weakens as low pressure
systems move into B.C.

Seas of 8 to 10 ft this afternoon will continue to subside, with
6 to 7 ft this evening, and down to 4 to 6 ft for Sun. The
increased east to northeast winds later today into Sunday will
create locally choppy seas at times.

High pressure over the offshore waters will dominate weather to
start next week, with lighter northerly winds and seas running 3
to 5 ft. Changes arrive later next week, as series of fronts
approach the region. Too early for much in details, but suffice
to say will see return of southerly winds by Thu and Fri.  -Rockey


PZ...Small Craft Advisory until 11 PM PDT Sunday for all
 coastal waters from Cape Shoalwater to Florence.



PZ...Small Craft Advisory until 11 PM PDT Sunday for coastal waters
     from Cape Shoalwater WA to Florence OR out 60 NM.

     Small Craft Advisory until 2 PM PDT this afternoon for Columbia
     River Bar.



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