462
FXUS66 KPQR 192334
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
434 PM PDT Tue Aug 19 2025


.SYNOPSIS...Onshore flow and near average temperatures Wednesday
will give way to building high pressure and produce a multi-
day stretch of hot temperatures and a mix of moderate and major
heatrisk for inland valleys Friday and Saturday. There is a
10-20% chance that the hot temperatures persist through Tuesday.


&&


.DISCUSSION...Tonight through Monday...Water vapor satellite
imagery reveals a shortwave trough over the northeast Pacific
and a shortwave ridge over the southern Rocky Mountains. This
will maintain low level onshore flow into Wednesday and keep
temperatures near to slightly above average.

Global ensembles are in good agreement the aforementioned Four
Corners high pressure will build northwestward into the Pacific
Northwest later this week into this weekend. This will result in
rather dramatic heat-up for inland valleys Thursday into
Friday. Before this happens we will have a period of overlapping
northerly winds and low relative humidity across the southern
half of the Willamette Valley Thursday afternoon and early
evening. A Fire Weather Watch has been issued given the fuels in
this zone primarily consist of grass and shrubs and will
sufficiently dry out by this time.

Flow will turn easterly across the Cascades and Columbia River
Gorge Thursday night and result in the thermally induced surface
trough spreading northward across the region on Friday. NBM and
global ensemble guidance is in good agreement most inland
valleys will be in the upper 90s to around 100F Friday and
Saturday with widespread moderate heatrisk across northwest
Oregon and southwest Washington. Pockets of major heat risk are
now in the forecast for the Portland/Vancouver metro and
Columbia River Gorge where confidence in warmer overnight low
temperatures exist. Either way, extra precautions will need to
be taken for those planning to run or walk in these hot
temperatures. Have a plan to make sure you can stay hydrated and
can easily cool off with cold wet towels or rags. The reason
major heatrisk is not more widespread at this point is that low
temperatures are still forecasted to be in the low to mid 60s at
most locations. However, there is a 30-40% chance that low
temperatures only end up in the mid to upper 60s and major
heatrisk becomes more widespread.

Ensembles are in general agreement temperatures will gradually
lower Sunday through the middle of the next week as high
pressure gradually shifts eastward and onshore flow increases
across the region. It should be noted that approximately 10-20%
of the global ensemble guidance suggests Friday and Saturday`s
hot temperatures will persist through Monday and/or Tuesday.
Again, this is not the most likely scenario, but it`s not
implausible either.


&&


.AVIATION...Current satellite and surface observations show low
stratus and a mix of LIFR to IFR conditions beginning to develop
along the central Oregon coast with degrading flight categories
anticipated along the rest of the coast this evening. This surge
of marine stratus/air will attempt slosh into the
Portland/Vancouver metro between 12-17z Wednesday with the latest
guidance suggesting a 20-40% chance for a MVFR CIGs during this
period. Otherwise, the rest of the inland sites maintain VFR
conditions. Winds remain fairly light, generally less than 10-15
knots at all sites.

PDX AND APPROACHES...Expect VFR conditions to continue through the
evening an most of the overnight period. We`ll still need to watch
for a potential period of MVFR CIGS 12-17z Wednesday morning with
around a 25-30% chance this occurs at PDX - slightly higher
probabilities near KTTD. High confidence in VFR CIGs/VIS 17-18z
onward through the rest of Wednesday. -Schuldt


&&


.MARINE...A fairly typically summertime pattern is expected moving
through the rest of the work week into the weekend as an area of
high pressure sits over the northeastern Pacific. On Wednesday the
pressure gradient across the waters will begin to tighten helping
to facilitate slightly stronger northerly winds as the day goes
on. Given the increasing probabilities for 21 knot or greater
gusts come Wednesday late afternoon evening through Thursday
across the inner and outer waters south of Cape Falcon, a Small
Craft Advisory was issued. It`s possible this advisory will need
to be extended for the outer waters through the end of the week as
northerly winds likely persist. Otherwise, seas generally stay
around 3-6 feet through the rest of the week with a dominate
period of 8-10 seconds. -Schuldt


&&


.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Fire Weather Watch from Thursday afternoon through Thursday
     evening for ORZ685.
WA...None.
PZ...Small Craft Advisory from 5 PM Wednesday to 5 AM PDT Friday
     for PZZ252-253-272-273.


&&


$$

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