Wildfire in Oregon, August 5 to 31, 2023

Area Forecast Discussion
National Weather Service Portland OR
230 PM PDT Sat Aug 5 2023

.SYNOPSIS...Cool and mostly cloudy along the coast, but still warm
inland again for Sunday. Scattered showers inland, along with a few
thunderstorms over the Cascades into tonight, perhaps again Sunday.
Then, back to dry weather for Monday, but front will bring cooler
onshore flow with spotty rain for Tue and Wed. Afterwards, high
pressure builds, bringing rather toasty temperatures to the region
next weekend.
&&

.SHORT TERM...(Tonight through Monday)...Broad area of low pressure
remains nearly stationary over north-central Oregon, with
counter-clockwise motion around it. As such, continue to see thicker
clouds along with embedded showers along and north of the Columbia
River, thanks to easterly flow. Afternoon instability still present,
enough such that will support a few isolated thunderstorms over the
Washington Cascades, Hood River Valley, and over Cascades crest as
far south as Santiam Pass. Farther to the south (such as Lane
County), flow is more westerly, and drier, giving partly to mostly
sunny skies. Though will see some building cumulus over the Cascades
of Linn and Lane County, think that will stay as such. Could see a
few showers or thunderstorms go up on the crest, but if does, would
drift eastward into the Deschutes basin fairly quickly. Not much
change in the overall pattern tonight, though showers will gradually
decrease overnight.

Upper low will continue to drift slowly eastward towards Idaho on
Sunday, with shower potential decreasing as the day progresses. Even
so, any shower potential likely to be only over the south Washington
Cascades and Oregon Cascades. Rest of the region will gradually
becoming partly to mostly sunny under dry but mild westerly flow
aloft. Not much change into Monday. Though there a weak system
pushing inland. Not much in way of moisture, though will keep small
chance PoPs (probability of 0.01 inch of precipitation), mainly for
the coast and into the Washington Cascades. But, this system will
maintain onshore flow, enough to maintain low clouds on the coast at
night into the mornings, and areas of low clouds well inland in the
mornings. Temperatures remain seasonal for early August, with 65 to
75 along the coast, and 80s inland.			 /Rockey

.LONG TERM...Tuesday through Friday night...Deterministic guidance
and their ensembles are in generally agreement of a frontal system
moving into the Pacific Northwest Tuesday to Wednesday. This would
lead to temperatures cooling down to the upper 70s/low 80s for inland
valleys. Precipitation chances also begin to increase, with PoPs of
20-40% inland and 40-60% along the coast and Coast Range. The highest
chances are found across southwest Washington and gradually lower to
the southeast towards eastern Lane County. There still remains
uncertainty with how far inland the front will push and the amount of
rain associated with it. The current NBM 4.1 run shows a 40-50%
chance of a quarter of an inch or greater of rain in the Astoria to
Pacific County area, a 15-20% chance from Salem to Portland, and a
5-10% chance near Eugene.

As we head further into next week, and particularly the following
weekend, the majority of global ensembles are suggesting the hottest
temperatures of the year so far will occur. NBM 4.1 is indicating a
30-50% chance of exceeding 100 degrees in the Willamette Valley on
Sunday, August 13 and a 50-60% chance of that same threshold on
Monday, August 14. CPC also suggests a 80-90% chance that
temperatures will be above normal between August 12 to August 18.
Normal temperatures are currently in the low to mid 80s for inland
valleys. The main uncertainty in the temperature forecast centers
around to what degree we will end up above normal...upper 80s, 90s,
or 100s.	-Alviz

&&

.AVIATION...00z TAFs: Broad and disorganized low pressure aloft
will persist over WA/OR through roughly 18z before pushing east of
the Cascades. The threat of a few isolated thunderstorms along the
Cascades will remain into this evening as sunbreaks destabilize
the air mass. Inland sites will remain VFR with slight chances of
a few isolated showers or virga possible into tonight. N-NW winds
along the coast will bring marine stratus onshore during the
overnight hours with a greater than 80% of LIFR ceilings pushing
into the coastal valleys. Conditions will improve along the coast
after 18z Sun.

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

KPDX AND APPROACHES...VFR with cigs likely remaining 5000 ft through
the TAF period. A few light showers or virga are possible at any
time. Isolated thunderstorms will be possible over the Cascades
this afternoon, but there is less than a 10% chance of
thunderstorms directly impacting the terminal.

&&

.MARINE...A decaying front will cross the waters disrupting the
tight gradient that brought breezy northerly winds over the waters
this evening. Expect winds in the 5 to 10 kt range Sunday into
Monday morning. High pressure will attempt to reestablish Monday
for a brief period before another weak front approaches the waters
Tuesday. Winds will become southerly Wednesday but no impacts are
expected.

Swell remains minuscule over the coastal waters over the next few
days, with seas likely 5 ft or less and primarily wind- driven
until modest W-NW swell associated with Gulf of Alaska low
pressure moves into the Pac NW waters midweek.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...None.

&&

www.weather.gov/portland

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