Wildfire in Oregon, September 1 to 30, 2022

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
845 PM PDT Wed Aug 31 2022

Updated Aviation discussion

.SYNOPSIS...High pressure over the western US will continue to bring
above average temperatures into next week. A couple weak upper level
storm systems brushing the region could squeeze out some drizzle
along the coast and possibly a thunderstorm over the Cascades,
particularly Friday night into Saturday morning.

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.SHORT TERM...Tonight through Friday...Water vapor satellite imagery
this afternoon reveals a shortwave trough sliding northeastward
across western Washington. Marine stratus remains across the coastal
waters this afternoon per visible satellite imagery. Expect this
marine stratus to congeal and spread into the Coast Range gaps
overnight, but likely fail to reach the Willamette Valley. With
500mb heights climbing back towards 590dm, we should see hot
temperatures continue into Thursday and Friday across the Willamette
Valley and Columbia River Gorge. With that said, between the upper
level flow turning more southerly Thursday night into Friday, 500mb
heights beginning to lower and surface pressure gradient forces
becoming more oriented from southwest to northeast across the CWA,
marine air should be able to infiltrate into the lower Columbia and
Willamette Valleys a bit more so Thursday night into Friday. As a
result, NBM guidance suggesting high temperatures only topping out
in the upper 80s on Friday looks on track. /Neuman

.LONG TERM...Friday night through Tuesday...There is increasing
ensemble support for a shortwave trough to eject northeastward across
the Pacific Northwest Friday night into Saturday. Given the pattern,
have opted to include a slight chance mention of thunderstorms from
the Mt Hood/Columbia River Gorge area and points northward during
that timeframe. Otherwise, this upper level system passing by the
area should allow marine clouds to spread inland and may also allow
for at least some patchy drizzle to form along the coast.

While all the members of the GEFS, EPS and CMCE are in good
agreement upper level ridging will remain in place across the
western US through the long term, there remain some subtle variation
in 500mb height fields over the Pacific Northwest between ensemble
members that bring uncertainty into temperatures and light
precipitation chances late in the weekend into early next week.
The good news is that there are relatively few ensemble members that
would suggest ridging will rebound back into the Pacific Northwest
that inland locations will warm into the 90s again. For example, NBM
probabilities of KPDX reaching 90F Sunday through Tuesday remains
below 20%. For those wanting rain, measurable rain chances generally
appear less than 10% in any given 12 hour period Sunday
through Tuesday at this point. /Neuman

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.AVIATION...06z TAFs: West to southwest flow aloft as upper ridge
of high pressure persists. At 03Z, marine stratus has solidified
along the coast and is quickly pushing through the Coast Range
gaps and up the lower Columbia River valley. IFR cigs at the coast
are expected to lower to LIFR by 06Z with deteriorating vsbys.
Chances that IFR stratus reaches inland terminals has increased to
around 30-40% between 13-17Z Thursday morning per 00Z HREF
guidance. Otherwise, VFR is expected to prevail inland under
mostly clear skies. Conditions at coastal terminals are likely to
see improvement around 18-20Z Thursday, with most locations
improving to VFR by 21Z.

For detailed Pac NW aviation weather information, go online to:
https://weather.gov/zse

KPDX AND APPROACHES...VFR conditions are likely to be predominant
throughout the forecast period, though there will be a 30-40%
chance for a period of IFR ceilings during the 13-17z timeframe
Thursday morning. Light northwest winds expected. /DH

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.MARINE...At 2 PM, visibilities had in general improved across
the waters, and if model guidance is correct in recognizing trends
through the evening these better visibilities will continue for
the next several hours. However, guidance is also suggesting
deterioration in visibilities will occur later this evening and
continue through at least mid morning Thursday, so the Dense Fog
Advisory will be allowed to continue through 10 AM Thursday.
Otherwise, marine conditions will remain fairly relaxed through
the foreseeable future, with significant wave heights staying
around 4 to 5 ft and winds less than 20 kt. -Bumgardner

For information about upcoming marine zone changes, go online to:
https://www.weather.gov/pqr/marinezone

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Dense Fog Advisory until 10 AM PDT Thursday for coastal waters
     from Cape Shoalwater WA to Florence OR out 10 nm.Columbia
     River Bar.

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