National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS66 KPQR 202158
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
258 PM PDT Thu Jul 20 2017

.SYNOPSIS...Clouds will continue to dissipate across the area into
the evening. High pressure will build in behind this system tonight
for less clouds and warmer temps Friday and Saturday. Strengthening
onshore flow is expected to bring a gradual cooling trend back to
near normal temps Monday and Tuesday. Longer range forecast models
hint at the potential for an upper trough with below normal temps
toward the middle of next week.

&&

.SHORT TERM...Today through Saturday...Accumulating rain has been
mostly confined to the coast and higher elevations. The only
exceptions were Kelso, McMinnville, and Vancouver, where one
hundredth fell. The Portland Airport has only received a trace so far
and while an isolated shower cannot be ruled out in the next few
hours, it is unlikely, which means PDX will likely continue the dry
streak. Otherwise, the stratocumulus deck is slowly eroding from SE
to NW across the area and most locations will be mostly sunny by
later this afternoon and into the evening.

High pressure will build in behind this front tonight and Friday,
while the air mass warms aloft. Flow will remain onshore Friday, but
not nearly as strong as today. The marine layer will likely become
shallower as 500 mb heights rise and compress marine inversions. As a
result, expect less in the way of low clouds Fri morning. Much of the
Willamette Valley may start off sunny Friday, aside from a few clouds
spreading up the Columbia to near PDX. 00z 850 mb temps rise from
about +8 deg C at Salem this afternoon, to +13 deg C by late Fri
afternoon, and to +16 deg C Sat afternoon. The combination of warmer
temps aloft, limited morning low clouds, and weaker onshore flow
should result in significantly warmer days Friday and Saturday. Temps
will likely rise back to near normal or slightly above normal Friday,
with the warming trend continuing into Saturday for highs approaching
90 inland. Coastal areas will remain seasonably cool with more
persistent cloudiness as enough onshore gradient will remain for
afternoon and evening seabreezes.  Weagle/Bentley

.LONG TERM...Saturday night through Wednesday...Models are starting
to come into better agreement in how to handle a weak upper low that
is expected to shear off from the tail end of today`s cold front in
the general vicinity of 35N/135W, though there are still small
differences in the details. Both the GFS and ECMWF now show the upper
low cutting off west of the California coast and then lifting NE into
Oregon by Monday night. This will leave a slight chance of afternoon
and evening thunder Sunday and Monday for the Cascades south of
around Santiam Pass. Flow aloft generally remains S-SW ahead of the
weak upper low/trough, which should keep thunder chances limited to
the Cascade crest and points east. Troughing persists through the
second half of the week which will keep temperatures at or below
normal. Weagle/Bentley

&&

.AVIATION...Clouds remained over much of nw OR and sw WA early this
afternoon west of the Cascades, but cigs were improving and were
largely VFR with just a few areas of MVFR remaining. Expect VFR
conditions to prevail over the interior tonight and Fri. Over the
coastal areas VFR conditions will dominate through early tonight,
but expect areas of IFR or low end MVFR conditions to develop after
09z as some stratus and fog develops, and continues until
midday.

KPDX AND APPROACHES...VFR conditions tonight and Fri. The chances
for MVFR cigs to redevelop late tonight or Fri morning between 12z
and 17z are around 10 percent.
&&

.MARINE...A ridge of high pres over the coastal waters will persist
into Sat. As a result, wind and sea conditions will remain benign
through Saturday. Northerly winds will increase with gusts into the
25 to 30 kt range Saturday night, and continue through Monday. Seas
will respond by building to 8 to 10 ft, with relatively short
periods, by late Sunday morning.
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.

&&


$$

Interact with us via social media:
www.facebook.com/NWSPortland
www.twitter.com/NWSPortland

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 forecast area.