293
FXUS66 KPQR 301813 AAB
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1112 AM PDT Wed Jul 30 2025

...Updated aviation discussion and WWA...

.SYNOPSIS...Highs around 90 degrees through the interior valleys
today. Showers and chance of thunderstorms develop across the
Cascades this afternoon, with chances persisting through Thursday
evening. Lower chances of light rain pushing into the Willamette
Valley later tonight through Thursday morning. Increased cloudiness
Thursday with temperatures moderating through the weekend. Slight
chances for light rain return early next week.

&&

.SHORT TERM...Today through Thursday...Another warm day expected
across the interior lowlands with afternoon highs around 90 degrees.
These temperatures will maintain a moderate HeatRisk through the
Willamette Valley, including the Portland/Vancouver Metro. Be sure
to stay hydrated and reduce time in the sun during the warmest part
of the day, if possible.

Also monitoring chances for showers and thunderstorms, mainly over
the Cascades this afternoon and evening. A weak disturbance will
lift northward initiating convection near the Cascade crest later
this afternoon, leading to a 15-30% chance of Thunderstorms, highest
across the Lane and Linn County Cascades. HREF guidance shows the
potential of CAPE values increasing to around 1000-2000 J/kg along
the Cascades. RAP forecast soundings show steep mid-level lapse
rates with DCAPE values exceeding 1000 J/kg, indicating potential
for stronger wind gusts associated with thunderstorms that do
develop. With flow aloft south to southeasterly, there remains low
chances for a stray shower or even a thunderstorm (less than 10%) to
expand over the foothills and drift over the Willamette Valley
overnight through Thursday morning.

A weak upper level low over northern California will continue to
lift north, drawing additional moisture into the region. Expect
increased cloudiness on Thursday, leading to temperatures cooling
somewhat into the upper 70s to lower 80s. Expect another round of
showers and potential thunderstorms over the Cascades Thursday
afternoon/evening, but with reduced surface heating, CAPE values
likely remain below 1000 J/kg, while PWAT values increase to around
1.0-1.2 inch. NBM guidance does show up to a 35% chance of
thunderstorms over the Lane County Cascades Thu afternoon. /DH

.LONG TERM...Friday through Tuesday...Not much change in the long
range forecast as a fairly quiet weather pattern returns through the
weekend. High confidence remains of temperatures warming into the
upper 70s to lower 80s each afternoon. The upper level synoptic
pattern maintains southwesterly flow aloft across the region with
low chances of afternoon showers and thunderstorms (20% or less)
near the central Oregon Cascade crest. By Monday, cluster analysis
of the model ensembles show potential for a deeper upper level
trough pushing across the Pacific NW, increasing onshore flow. Will
maintain the 10-20% chance of light rain early next week. But, there
remains around a 30% chance of upper level ridging returning to the
region by Tuesday. This is noted in the increasing uncertainty in
high temperatures toward the middle of next week, as the 10th-90th
percentile max temp ranges are between 75 to 90 degrees by
Wednesday. /DH

&&

.AVIATION...Satellite imagery and surface observations as of early
Wednesday morning depict MVFR marine stratus along the coast as well
as VFR conditions with high clouds across the Willamette Valley.
Could see some brief improvement to VFR along the coast this
afternoon with daytime heating, however, marine stratus will
continue to linger just offshore. There is more uncertainty with
whether or not KONP improves to VFR for a long period of time, so
opted for a TEMPO group to message intermittent MVFR/VFR
fluctuations. IFR/MVFR stratus likely (60-80%) returns along the
coast by 02-04z Thu. VFR conditions prevail inland. Northwesterly
winds around 5-10 kt across the region with gusts up to 18-20 kt
along the coast and most of the Willamette Valley. An exception
would be the southern Valley where winds shift more southwesterly
overnight.

Will note that there is a 15-30% chance for thunderstorms across the
Lane County Cascades, but only a low (5-10%) chance that any
thunderstorms from the Cascades moves into the Willamette Valley. If
a storm does move into the Valley, it may bring gusty winds and
brief heavy rain which could impact visibility.

PDX AND APPROACHES...VFR with SCT/BKN high clouds. Northwesterly
winds 5-10 kt.      -Alviz

&&

.MARINE...Minimal change in the overall weather pattern through
the remainder of the week as weak high pressure remains over all
waters. Expect benign seas of 2-4 ft with north/northwest winds
with gusts up to 20 kt.

&&

..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 breezy and erratic wind gusts. There is a
20-30% chance of thunderstorms Wednesday in the Willamette National
Forest Cascades. A Red Flag Warning at fire zones ORZ-689 and ORZ-
690 remains in effect between 11am - 11pm Wed. Lower confidence in
the second half of Wednesday night and Thursday, along with a
stronger onshore push with RH values increasing to around 70-80%
overnight, the previous Fire Weather Watch for those same zones
remains 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

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