140
FXUS66 KPQR 110923
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
223 AM PDT Sun Aug 11 2024

.SYNOPSIS...Westerly onshore flow will continue through this
week, bringing a cooling trend along with increasing morning
clouds and chances for light rain or drizzle at the coast.
Temperatures will fall to near or just below normal by Sunday,
lasting through next week. Onshore flow will also bring
improving air quality for most locations as smoke will be pushed
to the east, aside from areas immediately near and/or downwind
of ongoing wildfires. The return of rain chances is possible
late this week, though amounts look to be limited at this time.

&&

.SHORT TERM...Sunday through Saturday...Observations early
Sunday morning indicate onshore flow continues across NW Oregon
and SW Washington with west to northwesterly winds under fairly
zonal upper level flow. Satellite imagery shows marine stratus
pushing east along the western Coast Range foothills and
filtering inland along the Columbia River valley into the
Portland metro area and through Coast Range gaps. HREF
indicates a 40-60% chance of stratus filling in the Willamette
Valley by daybreak and slowly dissipating late morning through
early afternoon. A weak trough will begin deepening along the
Washington & Oregon coasts today, and this combined with the
cloud cover will allow daytime temperatures to fall back to near
normal today, low 80s in the Willamette Valley.

This upper trough continues deepening along the Western
coastline Monday before moving inland Tuesday. Daytime
temperatures will continue cooling to below normal Monday and
remain fairly steady Tuesday with mid to upper 70s across
inland valleys and low to mid 60s across the coast.
Additionally, some moisture associated with this trough will
allow for chances of drizzle and light rain along the coast late
tonight through early Tuesday. Could also see some drizzle over
the Cascades as the marine layer deepens under continued
onshore flow. NBM notoriously has a difficult time capturing
drizzle chances inland, so NBM PoPs remain less than 10%.
However, if any drizzle does occur over the Cascades,
accumulation would be very light.

Wednesday`s weather will be similar to today with temperatures
bouncing back to near normal under relatively zonal flow and
morning stratus under continued onshore flow. Ensemble guidance
is in good agreement of the general upper level pattern late
this week with all WPC 500mb clusters indicating longwave troughing
developing Thursday and continuing into the weekend with the
potential for multiple waves along the trough. Overall, this
pattern is likely to bring the return of rain chances for much
of the CWA as well as below normal temperatures. However,
uncertainty still remains within the ensembles and deterministic
models in the specific location and timing details of the main
trough and associated shortwaves, which is causing lower NBM
PoPs than expected. Latest guidance is indicating an amplified
wave moving west into Oregon on Thursday with confidence
increasing in showers and an isolated chance of thunderstorms
over the central Oregon Cascades. More widespread rain is
possible Friday and Saturday depending on the timing of the next
waves pushing into the region from the northwest. At this time,
rain amounts look to be pretty limited at less than 0.1-0.25
inch for most areas, but we will have to keep an eye on this
pattern. -HEC

&&

.AVIATION...Weak westerly flow aloft today while onshore flow
persists in the lower levels. Marine stratus again solidly filled
in along the coast with CIGs holding around 400-800 ft. The
profiler at Astoria also shows the marine layer has deepened to
around 3000 ft with some drizzle being reported at KAST. Expect at
least IFR conditions to persist at the coast through 18-20Z
Sunday, while there remains around a 40% chance of CIGs falling to
LIFR early this morning. Northwest winds with gusts up to 20 kt
this afternoon for the central OR coast.

Inland, again predominately VFR expected through the period, but a
stronger marine push up the lower Columbia has caused MVFR
stratus to develop at KPDX and KTTD as of 09Z Sunday. CIGs around
FL015 will likely persist there through 18Z this morning. Stratus
may continue to filter across the Willamette Valley this morning,
with probabilities around 60% for KUAO, and 30-40% for KSLE and
KEUG. NNW winds up to 10 kt inland this afternoon and evening,
except stronger through Coast Range gaps.

Smoke from wildfires burning across the region could result in
some slant range visibility issues.

PDX AND APPROACHES...MVFR stratus with CIGs around FL015 expected
to persist through 18-19Z Sunday. Then, VFR expected with
increasing high level clouds through this evening. Northwest
winds increase up to 8-10 kt this afternoon and evening. /DH

&&

.MARINE...High pressure offshore will maintain north to northwest
winds up to 15 kt across the coastal waters Sunday. Seas remain
choppy and primarily wind driven around 5 to 6 ft today. Then, the
surface high retrogrades west as a weak front drops south of of
the Gulf of Alaska on Monday. A broad area of weak low pressure
near Vancouver Island causes winds across the coastal waters to
shift more westerly on Monday, and veering southerly on Tuesday.
Seas expected to subside to around 2 to 4 ft by Tuesday. Fairly
benign conditions continue into Wednesday. /DH

&&

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

&&

$$

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