642
FXUS66 KPQR 040945
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
245 AM PDT THU SEP 4 2025
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 DEAMPLIFIES 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
GOING THROUGH THE TAF PERIOD EXPECT THE CONTINUATION
OF VFR CONDITIONS AT INLAND SITES. 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. LIKE YESTERDAY
(WEDNESDAY) THERE'LL BE A WINDOW FOR CIGS TO POSSIBLY LIFT TO
MVFR/VFR FOR A BRIEF PERIOD SOMETIME BETWEEN 20Z THU THROUGH 00Z
FRI WITH KAST THE BEST CANDIDATE TO SEE IMPROVEMENT DURING THIS
WINDOW. WINDS GENERALLY VARIABLE AND LESS THAN 10 KTS, BECOMING
NORTH TO NORTHWEST AFTER 18Z THU. CASCADE THUNDERSTORMS ARE
POSSIBLE AGAIN AFTER 20Z THU AS WELL.
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 - CIGS AOA 10-15KFT. WINDS GENERALLY REMAIN
BELOW 10 KNOTS. -SCHULDT
MARINE
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 11 AM PDT THIS MORNING FOR PZZ210-
251>253.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSPORTLAND
X.COM/NWSPORTLAND
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