Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 231715

Area Forecast Discussion
National Service Portland OR
1014 AM PDT Tue Jul 23 2019

.SYNOPSIS...Clouds are increasing this morning as an upper level
trough approaches. The cloud cover and stronger onshore flow will
result in cooler afternoon temperatures today. Spotty light
precipitation is not out of the question along the coast and in the
higher terrain, and there is a slight chance of thunderstorms late
this afternoon and evening along the Cascade crest. High pressure
builds back into the region for the latter half of the week, leading
to drier and seasonably warm temperatures.


.SHORT TERM...Today through Thursday...Coastal low clouds made a last
minute surge inland just after sunrise this morning, likely the
result of a rapidly deepening marine layer ahead of an approaching
upper trough and strengthening onshore flow. With the marine layer
deepening, suspect at least some cloud cover will be maintained for
the inland valleys through this afternoon. This will result in cooler
temperatures today, with highs generally topping out in the mid to
upper 70s despite a mild start to the day. There have also been a
couple reports of showers from the deepening marine layer, with
measurable rain already reported in Astoria and at Tidewater RAWS.
Therefore we added isolated showers to the forecast today for our
northern coastal areas and higher terrain. Thunderstorms are looking
less likely due to the stabilizing influence of the marine layer, but
still cannot rule out a stray thunderstorm right along the Cascade
crest. However the better chance of thunder looks to be confined east
of the crest, where deeper moisture and instability exist. With
steering flow from the S-SW, it is likely that any deeper convection
that develops later this afternoon would be pushed quickly N-NE of
our forecast area.

Remainder of short term discussion follows and is unchanged.  Weagle

Weak upper level ridging and surface high pressure looks to start
building into the Pacific NW late tonight and stick around for the
next couple of days. This will result in drier and warmer conditions
for Wednesday and Thursday. Light offshore winds look to also develop
along the central coast Wednesday which should help to mitigate
marine stratus. Unfortunately, light northwesterly winds will
continue across the north Oregon and south Washington coast so we
should continue to see marine stratus along the north coast and
locally inland across the northern half of the area Wednesday
morning. The thermal trough moves inland in the afternoon remaining
south of Lane County tightening the north-south surface pressure
gradient across the central and south Willamette Valley. This will
result in north winds gusting to 20-25 mph Wednesday afternoon in the
central and south Willamette Valley.

There will be much less (if any) marine clouds along the coast or
inland Wednesday night, and a sunnier start to the day on Thursday
will result in warmer afternoon temperatures (upper 80s inland,
lower-mid 70s coast). /64/TJ

.LONG TERM...Thursday Night through Monday...Guidance continues to
keep the bulk of the energy to our north through the weekend for
mostly dry weather and seasonal temperatures. The best chance for a
strong marine push along with some light rain or drizzle is across SW
Washington late Friday into early Saturday as a weak front brushes
by. Will also see periods of late night/morning stratus along the
coast and portions of the interior, generally along the lower
Columbia River. Otherwise, expect plenty of sun across the region
through the weekend, with inland temperatures peaking in the 80s.


.AVIATION...MVFR cigs expected to remain through at least 18Z
Tuesday and slowly lift to VFR. Isolated showers through the day
along coast primarily north of KONP. These showers have the
potential to bring periods of MVFR cigs and vis to the coast, but
should be brief in nature. Along the Cascades look for some
isolated showers with a slight chance of thunderstorms developing
after 18Z Tuesday as daytime heating starts. Inland locations
should return to predominantly VFR conditions. The marine layer
could redevelop overnight but that will be contingent on the
strength of the upper level trough passing over today. Current
models are in disagreement on if the marine layer will mix out or
not. Expect a better idea of what will happen by the afternoon
forecast package.

KPDX AND APPROACHES...Expect MVFR cigs to remain through 18Z.
Then VFR conditions are expected this afternoon and tonight.
Breezy NW surface winds will develop this afternoon and evening.


.MARINE...Typical summer-time northwesterly winds will continue
through most of the week. Winds will generally remain 15 kt or
less through Wed morning. A thermal trough over northern
California and southern Oregon will build on Wed and Thu, while
the NE Pac high also increases in strength. This will result in
some gustier northerly winds during the afternoon and evening
hours. The strongest winds will generally remain over
PZZ255/PZZ275, where small craft advisories may be needed on Wed
and Thu. Winds weaken a little Fri going into the weekend.

Seas will remain around 3 to 4 ft today. They will likely
increase a foot or two starting Wed afternoon in response to the
increasing winds. They will then remain around 5 to 6 ft through
the rest of the week. Pyle





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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 forecast area. is the U.S. government's official web portal to all federal, state and local government web resources and services.