Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 210331
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
830 PM PDT Sat Oct 20 2018

.SYNOPSIS...High pressure over the region will continue to produce
mild days, cool nights and mostly clear skies, with the exception of
some patchy morning fog and low clouds, through Monday. A more active
storm track brings cooler and wetter weather starting on Tuesday and
continuing through most of next week.

&&

.SHORT TERM...Tonight through Tuesday...No changes. Previous
discussion follows. It`s another beautiful fall day across SW
Washington and NW Oregon. Strong upper level high pressure remains
entrenched over the Pac NW. This resulted in a strong low level
inversion today, along with more morning fog and low stratus across
much of the lowlands. The clouds have broken up for pretty much
everyone at this point and skies are mostly sunny across the region.
Expect highs again to top out in the upper 60s to low 70s for the
interior, with low 60s at the coast. Above the inversion, many
stations in the higher terrain of the Cascades and Coast Range are
already well up in the 70s and a few spots may make a run at 80.

There is some easterly flow developing above the inversion through
the gorge today, which can be seen in a wind profiling radar in
Troutdale at about 1500 to 2000 ft above the surface. It`s beginning
to look likely that the inversion today will be too strong to allow
any of these offshore winds to surface at the lowest elevations.
Despite the modest offshore gradient showing up in the models
tonight, we are inclined to think that winds will again be fairly
light at the surface again tonight. Will keep a generally persistence
forecast for fog and low clouds for late tonight into Sun morning.
Then expect Sunday to be a near repeat of today. The only exception
will be that stratus clouds should be increasing along the coast. In
fact, some of our high resolution models are suggesting a weak
southerly wind surge will work up the coast late tonight and Sun
morning.

By Monday the upper level ridge axis will be pushing east into the
Intermountain West. If the southerly wind surge does not occur along
the coast tomorrow, it definitely will on Mon. This will result in
low clouds along the coastal areas that should persist through most
of the day. However, the interior looks to be in for one more sunny
and dry day Mon, with highs again into the low 70s. The coast will
likely be limited to highs in the 50s.

By Tue, the first frontal system in quite some time will be moving
onshore. The system will be weakening as it makes landfall.
Confidence remains fairly high that the coast and coastal mountains
will see measurable precipitation, although amounts should not be
overly impressive. The models have been trending weaker and weaker
with the front east of the Coast Range. At this point, it appears
that most of the interior lowlands can expect to see a few hundredths
out of this system at most. Pyle

.LONG TERM...Tuesday night through Saturday...No changes. Previous
discussion follows. The Tue front will usher in a period of more
active and typical cooler and cloudy late October weather that will
likely last through the rest of the week. A few showers will likely
linger Tue night behind the frontal passage. Another weak upper
level impulse is shown moving through the CWA on some of the models
Wed. This feature could generate another round of shower activity
during the day Wed, but confidence in this occurring is not high and
PoPs were limited to chance or lower at this time.
Then confidence is much higher that a more organized frontal system
will arrive late Wed into Thu. Model agreement is good that we will
see widespread measurable rain during this period. A strong surface
low is modeled to develop off the B.C. coast with this system, which
could result in some rather breezy winds along our coastal zones Thu
as well. Some lingering showers are possible Thu night into Fri. But
it then appears that a period of shortwave ridging will develop later
Fri into the weekend. If the models hold, this would provide us with
another brief period of warmer and drier weather for at least Sat.
Pyle

&&


.AVIATION...Generally VFR conditions across nw OR and sw WA late Sat
evening. similar to the past coule of days, expect IFR conditions
with areas of fog and low stratus to develop late tonight and early
Sun between 07Z and 13Z. Best bets for the fog and stratus will be
along the coast, the lower Columbia, and the north end of the
Willamette Valley. Fog and stratus expected to lift, with conditions
improving back to VFR generally between 17Z and 20Z.

KPDX AND APPROACHES...VFR conditions expected to give way to LIFR
conditions as fog and low stratus form between 09Z to 12Z. After
several hours of IFR conditions, VFR conditions return, most likely
between 17Z and 20Z.

&&

.MARINE...No changes. Previous discussion follows. High pressure
remains over the waters this afternoon. The surface thermal trough
has been very slow to build north, which has kept winds just below
20 kt. Still think it will build north this afternoon, so am leaving
the Small Craft Advisory out for a few more hours. If it never
materializes, we may cancel it early. If winds develop, gusts to 20
to 25 kt should stay south of Garibaldi. Winds diminish later
tonight into Sunday morning, remaining 15 kt or less through Monday
night.

We will see a major pattern change to a more active pattern
starting early next week with a cold front which moves across the
waters on Tuesday. Expect winds to turn southerly ahead of this
system Monday evening, with winds gradually increasing going into
Tuesday. Southerly winds gusting to 25 to 30 kt appear likely as
the front moves across the waters midday Tuesday. We will have
another front move through on Thursday, which looks slightly
stronger. Models suggest a ridge may try to build back up going
into next weekend, but doesn`t look as strong or as persistent
as the ridge we`ve been dealing with for the past week.

Seas, which right now are running around 5 to 6 feet will
increase to 9 to 10 feet on Tuesday as the front moves through.
Behind the front, a westerly swell keeps seas up around 8 to 9
feet until the next front moves through on Thursday, when seas
may build into the lower teens. -McCoy


&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds until midnight PDT 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. This area is



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