465
FXUS66 KPQR 300528 AAA
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1028 PM PDT Tue Jul 29 2025

.SYNOPSIS...Temperatures in the interior valleys warm into the upper
80s to lower 90s today and Wednesday. Thunderstorm chances will
persist along the Casacdes each afternoon, with highest chance
Wednesday and Thursday. Temperatures moderate through the weekend
and into early next week.

&&

.SHORT TERM...Today through Thursday...A low south of the Gulf of
Alaska combined with weakening high pressure east of the Cascades is
producing southerly flow over the region, bringing in warm moist air
aloft. This will produce warm temperatures both today and Wednesday,
with recurring thunderstorms primarily in the southern Oregon
Cascades through the rest of the workweek.

Daytime high temps both today and Wednesday will be elevated, with
850 mb temps around 20 degrees C. Surface temps in the afternoon both
today and Wednesday will reach the lower 90s in the Willamette
Valley. The coast is much cooler, with highs around the mid to upper
60s. Widespread minor to moderate Heat Risk is expected both days; be
sure to stay hydrated and reduce time in the sun during the warmest
part of the day, if possible.

Recurring thunderstorms are expected during this period each
afternoon and evening. Tuesday`s thunderstorms look limited to the
Lane County Cascades, with a 15-25% chance right at the Cascades
crest. On Wednesday, a small low system developing in northern
California pushes northward into our region, eventually exiting by
Thursday afternoon. This will spur more likely and more widespread
thunderstorms from midday Wednesday until Thursday evening. Wednesday
afternoon and evening see a 20-35% chance of thunderstorms at the
Lane and Linn County Cascades. Fairly robust CAPE values around
1000-1500 J/kg in the Cascades can be expected, though CIN values
look to remain too high (-200-400 J/kg) west of the Cascades for any
significant concerns outside of the Cascades Wednesday.

Wednesday night sees somewhat more uncertainty, with many global
ensemble models showing a decrease in thunderstorms in the latter
half of Wednesday night. NBM shows thunder probs dropping below 10%
for all areas between 11pm Wed and 11am Thu. However, some
high-resolution guidance (UWWRF, HREF) indicates nocturnal
thunderstorms may continue, pushing further northward up into the
south Washington Cascades. Thursday afternoon and evening see an
increase in thunderstorms regardless, but with lower certainty as to
exact location. 12 hr NBM thunder probs from 11am-11pm Thu show
around a 30% chance of thunderstorms in the Lane and Linn County
Cascades, with a 10-20% chance of thunderstorms further north from
Marion County, OR to Skamania County, WA. With a more moist surface
profile Thursday compared to Wednesday, slightly better chance of
rain showers associated with thunderstorms at that time. /JLiu

.LONG TERM...Friday through Monday...A fairly quiet weather pattern
returns through the weekend, with high confidence of temperatures
warming into the upper 70s to lower 80s each afternoon. Model
ensembles and 500 mb cluster analysis indicate a weak troughy
pattern persists, with southwest to westerly flow aloft. There is
around a 10-20% chance of light rain early next week as models and
their ensembles show potential for weak frontal activity moving
across the Pacific Northwest. /DH

&&

.AVIATION...High pressure and low level northwesterly flow will
maintain VFR conditions for inland terminals through 06z Thursday.
Upwelling along the coast will allow fog and low clouds to develop
along the coast overnight. High resolution model guidance does
suggest a 70-80% chance that IFR to LIFR conditions will develop
along the coast over the next few hours. Any breaks in low clouds
along the coast should be relatively short lived between 18z
Wednesday and 03z Thursday. There is a 30-40% chance of a
thunderstorm developing at any given point near the crest of the
Cascades south of Mt Jefferson between 21z Wednesday and 03z
Thursday. A low probability thunderstorm threat of 10-20% chance will
expand northwestward across the lowlands of northwest Oregon and
southwest Washington after 06z Thursday.

PDX AND APPROACHES...High pressure and low level northwesterly flow
will maintain VFR conditions through 06z Thursday.

&&

.MARINE...High resolution weather models suggest a 60-70% chance
for fog and low clouds to develop along the inner waters overnight,
which would necessitate a dense fog advisory. Given that reality has
been slow to catch up to the weather models, will hold off an
advisory until (if) it begins developing more widely.

Relatively benign seas of 2-4 ft look to persist for much of the
next week. Wind gusts generally look to remain 20 kt or less during
this time.

&&

..FIRE WEATHER...Increased instability combined with monsoonal
moisture will promote heightened thunderstorm potential. With
somewhat drier surface conditions, thunderstorms have the potential
to be on the dry side. With high confidence (30-35%) regarding
thunderstorms Wednesday in the Willamette National Forest Cascades,
the previous Fire Weather Watch has been upgraded to a Red Flag
Warning at fire zones ORZ-689 and ORZ-690 between 11am - 11pm Wed.
Lower confidence in the second half of Wednesday night and Thursday,
with the previous Fire Weather Watch for those same zones remaining
in place from 11pm Wed to 11am Thu. Thunderstorms continue through
Thursday evening, but with lower confidence regarding exact
locations; the Willamette National Forest still sees a 20-30% chance
of thunderstorms, but areas as far north as Skamania County, WA
could see a 10-20% chance of thunderstorms as well. However, with
increased low level moisture, the likelihood of wet thunderstorms
will be higher on Thursday compared to Wednesday.



&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 11 AM to 11 PM PDT Wednesday for ORZ689-
     690.
     Fire Weather Watch from Wednesday evening through Thursday
     morning for ORZ689-690.
WA...None.
PZ...None.


&&


$$

www.weather.gov/portland

Interact with us via social media:
www.facebook.com/NWSPortland
x.com/NWSPortland