986
FXUS66 KPQR 041721 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1021 AM PDT Thu Sep 4 2025

Updated Aviation and Marine Discussions

.SYNOPSIS...High pressure inland will continue to drive hot
weather across much of the region through Friday, with
widespread Moderate HeatRisk inland. Low chances of afternoon
and evening Cascade thunderstorms continue today, becoming more
widespread Friday and possibly Saturday. A shift in the pattern
will then bring cooler and wetter weather by early next week.

&&

.SHORT TERM...Now through Friday Night...A compact and
weakening upper low located just offshore of northwestern Oregon
early this morning per latest water vapor satellite imagery
will continue to track northward through today while upper
ridging over the Interior Northwest begins to break down.
Despite the departing low, heights aloft will fall through the
period and ample elevated instability will remain across the
region. Surface heating in the Cascades may provide enough lift
to break the low-level cap, however only isolated thunderstorms
are expected through this afternoon and evening. Mid-level winds
remain out of the southeast, so storms developing over the
higher terrain could track toward the foothills or Willamette
Valley locales. Minimum surface humidity looks to remain above
critical values, generally 30-45% across inland areas, so fire
weather concerns do not rise to the level of Red Flag Warnings,
however isolated dry thunderstorms, particularly among receptive
fuels in the Cascades, do pose some risk for new fire starts.

Otherwise, modest high cloud cover will again limit insolation
and prevent extreme heat across the region, resulting in
afternoon highs most likely in the mid to upper 80s across most
inland low elevations, with the southern Willamette Valley,
Columbia Gorge, and Hood River Valley the most likely to reach
into the low 90s. Overnight cooling to lows in the mid 50s to
mid 60s tonight will see adequate relief from the heat and only
Minor to Moderate HeatRisk for most. The Heat Advisory for the
Columbia Gorge Hood River Valley therefore remains in effect
only through 8 PM this evening.

On Friday, temperatures continue to trend slightly cooler as the
ridge de-amplifies while a negatively-tilted upper trough digs
off the coast of northern California and southwestern Oregon.
This feature could provide more robust forcing for convection,
with CAMs suggesting higher coverage of potential thunderstorms
over the Oregon Cascades while areas to the west are more
likely to remain capped. Available moisture will vary greatly
across the region, with precipitable water values of 0.6-0.8" in
the Cascades, 0.75-1" over Cascade foothills, and 1-1.25" from
the Willamette Valley west to the coast. This setup again raises
the risk of storms developing in the Cascades or foothills in
the afternoon which may initially produce dry lightning. -Picard


.LONG TERM...Saturday through Wednesday...A closed upper low
will develop just offshore over the northeastern Pacific this
weekend before moving inland early next week, producing a rapid
shift to cooler and wetter conditions. High temperatures around
80 degrees in inland valleys on Saturday are very likely
(75-95% chances) to remain in the 70s Monday through midweek. As
the upper low moves overhead Monday into Tuesday, nearly all
long-range ensemble members now depict accumulating rainfall
across northwestern Oregon and southwestern Washington, with a
50-75% chance of precipitation totaling 0.1" or more. -Picard

&&

.AVIATION... VFR conditions will persist for inland locations
through the TAF period. However, smoke and haze from wildfires in
the region may drop visibility between 6-10 miles at times.
Current observations show a mix of LIFR to IFR across the coast
due to persistent marine low stratus and those lowered flight
conditions are expected to persist through the majority of the TAF
period. However, there will be a window for flight conditions
along the coast, to improve towards MVFR/VFR for a brief period
between 20Z Thu through 00Z Fri with KAST the best candidate to
see improvement. Winds generally variable and less than 10 kts,
becoming north to northwest around 18Z-20Z Thu. Cascade
thunderstorms (15-20% probability) after 20Z Thu through 06Z Fri.

If traveling over the Cascades, be aware of smoke/haze from
wildfires over the region.

PDX AND APPROACHES...VFR conditions persist with high cloud cover
streaming overhead. Winds generally remain below 10 knots.
/42-Schuldt

&&

.MARINE...UPDATE: Extended the current Dense Fog Advisory for the
Inner Waters and Columbia River Bar through 0300 Friday.

Expect a ridge of surface high pressure residing over the far
eastern pacific to drive conditions today, mainly leading to
increasing northerly winds during the afternoon and evening hours
- gusts up to ~15-20 knots. It`s also worth highlighting the
surface high pressure will increase the probability of dense fog
across the inner waters this morning as well, although so far it
has largely remained just a low stratus deck. Then, beginning
later Friday into the weekend the surface ridge feature slowly
decays ahead of abroad area of low pressure from the Gulf of
Alaska progressing southward towards the area. Thus, winds
decrease as a result Friday onward in addition to a switch to
southerly winds on Saturday into Sunday. With all this in mind,
seas likely hold around 4-6 ft through Friday before subsiding to
2-4 ft over the weekend and into early next week. However, we may
see the return of 5ft+ seas around Wednesday of next week
associated with the arrival of the fresh northwesterly swell.
-Schuldt

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Heat Advisory until 8 PM PDT this evening for ORZ120>122.

WA...Heat Advisory until 8 PM PDT this evening for WAZ209-210.

PZ...Dense Fog Advisory until 3 AM PDT Friday for PZZ210-251>253.

&&

$$

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