Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 230323 AAA
AFDPQR

Area Forecast Discussion...Updated
National Weather Service Portland OR
823 PM PDT Sat Sep 22 2018

Updated aviation section

.SYNOPSIS...Showers will decrease tonight. Dry but seasonally cool
weather is expected for Sunday. High pressure and offshore winds will
result in warm and dry weather Tuesday through Friday. More seasonal
weather returns  next weekend.

&&

.SHORT TERM...Tonight through Tuesday...A short wave upper trough
will maintain a chance for showers late this afternoon and evening
behind a departing front. The best chance for showers is  to the
north and over the higher terrain. Rainfall totals are not expected
to be high, but an unstable airmass may result in isolated moderate
to heave showers. Expect rainfall totals to generally be light
tonight though (less than 0.10 inch).  The showers will be confined
to the higher terrain tonight, and end near or just after midnight.

Dry N-NW flow will gradually clear skies on Sunday, the first day of
Autumn, and the departing upper trough will keep the afternoon
temperatures below 70 degrees in most locations. High pressure builds
aloft Monday and Tuesday as a surface thermal trough expands up the
coast from California. Offshore winds should develop Monday night and
hold through Tuesday supporting clear skies and warming temperatures.
Interior daytime temperatures will peak in the mid 70s on Monday and
low 80s on Tuesday .Coastal regions likely warm into the 70s Tuesday
afternoon. ~TJ

.LONG TERM...Tuesday night through Saturday...Strong ridge remains
in place through much of next week. Both the GFS and ECMWF start to
break down the ridge late next week, but in two different ways. The
ECMWF brings the low off the coast of California north up into
Oregon, while the GFS brings a strong trough down out of Alaska/B.C.
to break down the ridge.  These two different scenarios bring a lot
of uncertainty to the forecast going into next weekend.

With the ridge in place through much of this week, expect continuing
offshore winds and abnormally warm temperatures through Thursday.
Friday is when both models start to break down the ridge in place
over the area, which should mean cooler temperatures starting Friday
going into next weekend. Both models keep us dry through at least
Saturday, but temperatures should drop down to be closer to normal
Friday and Saturday. -McCoy

&&

.AVIATION...Surface trough continues to move east of the Cascades
this evening, with a few lingering showers over the forecast area.
Expect mostly VFR conditions this evening to give way to a mixture
of IFR and MVFR conditions along the coast after 06Z and MVFR cigs
in the interior after 10Z as the air mass stabilizes due to plenty
of low level moisture. With skies clearing behind the trough cannot
rule out a brief period of patchy fog along the coast and interior
valleys tonight through Sunday morning, but confidence is too low to
include in the upcoming 06Z TAF package. Expect any reduced flight
conditions to improve by late Sunday morning, with VFR conditions
expected Sunday afternoon and evening.

KPDX AND APPROACHES...Mainly VFR the next 24 hours, but a few hours
of MVFR stratus is possible between 12-18Z. There is a chance that
patchy fog may impact the terminal Sunday morning as skies clear
behind the departing trough, but confidence is too low at this time
to include in the upcoming 06Z TAF. /64

&&

.MARINE...Wind speeds slowly decreasing early this afternoon and
will allow the small craft advisory for wind to expire. Wind
speeds continue to diminish this evening through tonight. North
wind develops over the waters Sun and continues through early
next week. A surface thermal trough forms over the South Oregon
waters Sun and then expands a little more north Sun night. Gusts
to 25 kt likely across PZZ275 beginning Sun night and possibly
getting close to 30 kt Mon and Mon night. Small craft advisory
wind conditions likely to spread into PZZ270 by Mon afternoon.
Model solutions show larger variations for the latter half of
next week. Used the GFS in the Thu-Sat time frame, which
maintains NW-N wind 10 to 20 kt over the waters. However,
confidence is low for any single solution.

Seas generally 8 to 10 ft across the north waters early this
afternoon. Expect little change through the evening. Periods 8
to 9 seconds will result in steep, choppy sea conditions and will
maintain the small craft advisory for hazardous seas. Wave
heights start to ease tonight. Increasing north wind Sun night
through early next week will produce choppy wind-driven sea
conditions, mainly south of Newport. Weishaar

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for hazardous seas until 10 PM PDT this
     evening for Coastal Waters from Cape Shoalwater WA to
     Cascade Head OR out 60 NM.

     Small Craft Advisory for Rough Columbia River Bar until 6 PM
     PDT this evening.

&&

$$

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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
commonly referred to as the CWA or forecast area.


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