948
FXUS66 KPQR 241133
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
400 AM PDT THU SEP 24 2026
SYNOPSIS
AFTER PLEASANT WEATHER TO START THE DAY THURSDAY, AN
INCOMING LOW PRESSURE SYSTEM WILL BRING AN ABRUPT TRANSITION TO COOL,
RAINY, AND WINDY CONDITIONS BEGINNING LATE THURSDAY AFTERNOON AT THE
COAST AND LATE THURSDAY EVENING INLAND. REMAINING COOL AND WINDY ON
FRIDAY WITH PERIODS OF RAIN. AFTER WIDESPREAD SOAKING RAIN COMES TO
AN END LATE FRIDAY, HIGH PRESSURE WILL BRING A QUICK RETURN TO DRY
AND QUIET FALL-LIKE WEATHER FRIDAY NIGHT THROUGH THE WEEKEND. CHANCES
FOR RAIN INCREASE SLIGHTLY EARLY NEXT WEEK, MAINLY OVER SOUTHWEST
WASHINGTON AND ON THE COAST.
SHORT TERM...NOW THROUGH FRIDAY NIGHT
CONDITIONS WILL START OFF
DRY AND CALM THURSDAY MORNING WITH GRADUALLY INCREASING HIGH CLOUDS.
HIGH CLOUDS WILL BE INCREASING AHEAD OF AN INCOMING LOW PRESSURE
SYSTEM THAT IS SET TO BRING AN ABRUPT TRANSITION TO COOL, WET, AND
WINDY CONDITIONS BEGINNING LATE THURSDAY AFTERNOON AT THE COAST AND
LATE THURSDAY EVENING FOR INLAND AREAS. THE SURFACE LOW ASSOCIATED
WITH THIS SYSTEM IS ALREADY EVIDENT ON SATELLITE IMAGERY WITH AN AREA
OF CIRCULATION BEGINNING TO TAKE SHAPE AROUND 400-500 MILES OFFSHORE
FROM THE CENTRAL OREGON COAST. SURFACE ANALYSIS SUGGESTS THE CENTRAL
PRESSURE OF THIS DEVELOPING LOW IS CURRENTLY AROUND 1008 MB. MODEL
ENSEMBLE GUIDANCE IS NOW IN BETTER AGREEMENT IN HOW THIS LOW WILL
EVOLVE OVER THE NEXT 24-36 HOURS, SUGGESTING THE LOW WILL DEEPEN AS
LOW AS ~995-1000 MB AS IT PROGRESSES EAST-NORTHEASTWARD TOWARDS THE
CENTRAL/NORTHERN OREGON COAST LATE THURSDAY INTO EARLY FRIDAY
MORNING. THE EURO AND GFS ENSEMBLES DEPICT NOTABLE ENSEMBLE MEMBER
CLUSTERING FOR LOW CENTER LOCATIONS, WITH THE LOW MAKING LANDFALL AT
THE COAST SOMEWHERE BETWEEN NETARTS, OREGON AND PACIFIC BEACH,
WASHINGTON, WITH THE MOST LIKELY LOCATION BEING NEAR ASTORIA. AS THIS
LOW APPROACHES THE COAST, AN EASTWARD-MOVING OCCLUDED FRONT AHEAD OF
THE LOW CENTER WILL BRING THE FIRST ROUND OF MODERATE STRATIFORM RAIN
TO THE AREA. RAIN WITH THIS FRONTAL PASSAGE WILL MOST LIKELY BEGIN
SOMETIME BETWEEN 3-7 PM PDT THURSDAY AT THE COAST AND BETWEEN 6-11 PM
PDT THURSDAY FOR THE COASTAL MOUNTAINS, WILLAMETTE VALLEY,
PORTLAND/VANCOUVER METRO, AND COWLITZ VALLEY. NOTE RAIN SHOULD BEGIN
CLOSER TO 6 PM PDT OVER THE COASTAL MOUNTAINS AND CLOSER TO 11 PM PDT
OVER THE VALLEY. AFTER 11 PM THURSDAY, RAIN WILL SPREAD OVER THE
COLUMBIA RIVER GORGE, UPPER HOOD RIVER VALLEY, AND
CASCADES/FOOTHILLS. HI-RES MODEL GUIDANCE SUGGESTS STEADY MODERATE
RAIN WILL THEN TRANSITION TO OFF-AND-ON LIGHT RAIN SHOWERS BEHIND THE
OCCLUDED FRONT THURSDAY NIGHT BEFORE SHOWERS BECOME HEAVIER AND MORE
FREQUENT FRIDAY MORNING AND AFTERNOON AS A COLD FRONT EXTENDING
NORTH-SOUTH ALONG THE SOUTH SIDE OF THE LOW CENTER MOVES INLAND ALONG
WITH THE CENTER OF THE LOW ITSELF. NOTE THERE IS ALSO A 10-20% CHANCE
OF ISOLATED THUNDERSTORMS FRIDAY AFTERNOON AS SURFACE-BASED
INSTABILITY INCREASES SLIGHTLY WITH COOLER AIR ALOFT MOVING IN. GIVEN
THE FAVORABLE LOW-LEVEL SHEAR ENVIRONMENT IN PLACE, AN ISOLATED COLD
CORE FUNNEL CLOUD CANNOT BE RULED OUT WITH ANY STRONGER SHOWERS OR
THUNDERSTORMS THAT DEVELOP ON FRIDAY, EVEN IN THE ABSENCE OF
LIGHTNING. GUSTY AND ERRATIC OUTFLOW WIND GUSTS OVER 40 MPH ARE
POSSIBLE AS WELL WITH SHOWERS AND STORMS, WITH DETAILS ON THIS
DISCUSSED BELOW.
IN REGARDS TO POTENTIAL IMPACTS WITH THIS STORM SYSTEM, WIND WILL BE
THE MAIN CONCERN AS THE SURFACE LOW MOVES INLAND AND BRINGS
INCREASING SOUTH TO SOUTHWEST WINDS. THE WINDIEST CONDITIONS ARE
EXPECTED TO OCCUR BETWEEN 3 AM AND NOON PDT FRIDAY MORNING.
CONFIDENCE IS HIGH (70-90% CHANCE) MAXIMUM WIND GUSTS UP TO AT LEAST
30-40 MPH WILL OCCUR DURING THAT TIME, STRONGEST AT THE COAST, OVER
HIGHER TERRAIN, AND IN THE CENTRAL/NORTHERN WILLAMETTE VALLEY.
CONFIDENCE IS RELATIVELY LOWER FOR MORE IMPACTFUL MAX WIND GUSTS OVER
40 MPH, AS WIND GUSTS OF THIS MAGNITUDE WOULD MOST LIKELY BE
ASSOCIATED WITH OUTFLOW WINDS FROM STRONGER CONVECTION (ESPECIALLY
FOR INLAND AREAS AWAY FROM THE COAST). PROBABILITIES FOR MAX WIND
GUSTS OVER 40 MPH RANGE BETWEEN 25-50% FOR MOST INLAND VALLEY
LOCATIONS, EXCEPT 50-65% OVER THE CENTRAL WILLAMETTE VALLEY AND SALEM
AREA. CHANCES RANGE BETWEEN 55-75% AT THE COAST, WITH THE HIGHEST
CHANCES NORTH OF YACHATS. EXPOSED HIGHER TERRAIN IN THE COAST RANGE
AND CASCADES IS MUCH MORE LIKELY TO SEE WIND GUSTS OVER 40-45 MPH
EVEN AWAY FROM CONVECTION (60-80% CHANCE, MAINLY TO THE NORTH OF LANE
COUNTY). REGARDLESS OF THE EXACT OUTCOME, AT LEAST SOME ISOLATED
REPORTS OF TREE DAMAGE AND POWER OUTAGES ARE LIKELY TO OCCUR WITH
THIS LOW PRESSURE SYSTEM, ESPECIALLY GIVEN THE FACT THAT LEAVES ARE
STILL ON TREES. HIGH-IMPACT WIND GUSTS OVER 55 MPH ARE UNLIKELY
(1-10% INLAND, 15-30% CHANCE AT THE COAST). HOWEVER, IT IS CLEAR WIND
GUSTS OF THAT MAGNITUDE ARE WITHIN THE REALM OF POSSIBILITIES, MAINLY
AT THE COAST ON THE SOUTH SIDE OF THE LOW CENTER AS IT MOVES INLAND
IF A STING JET DEVELOPS. MORE WIDESPREAD DOWNED TREES AND POWER
OUTAGES WOULD ENSUE IF THIS WERE TO OCCUR, SO COASTAL AREAS WILL BEAR
CLOSE MONITORING AS THE LOW APPROACHES LATE THURSDAY TO SEE IF
POTENTIAL WIND HEADLINES NEED TO BE ISSUED LATER TODAY.
FORECAST RAINFALL AMOUNTS OVER 36 HOURS FROM MIDDAY THURSDAY
THROUGH FRIDAY EVENING HAVE DECREASED SLIGHTLY TO 0.35-0.55 INCHES
WITHIN THE WILLAMETTE VALLEY AND PORTLAND METRO, WITH THE LOWEST
AMOUNTS IN THE SOUTHERN WILLAMETTE VALLEY. RAINFALL AMOUNTS ARE
LIKELY TO BE HIGHER ALONG THE COAST, IN THE COWLITZ VALLEY, IN THE
COAST RANGE AND WILLAPA HILLS, AND IN THE CASCADES, WHERE 0.6-1.2
INCHES ARE EXPECTED. WHILE THESE ARE "MOST-LIKELY" RAINFALL TOTALS,
THE DISTRIBUTION OF RAIN SHOWERS ON FRIDAY WILL RESULT IN SOME AREAS
SEEING HIGHER TOTALS THAN THAT WHILE OTHERS SEE LESS. AREAS THAT
OBSERVED FREQUENT HEAVIER SHOWERS AND/OR A THUNDERSTORM OR TWO MAY
SEE OVER 1.25-1.5 INCHES OF RAIN, WHILE THOSE THAT MISS OUT MAY
INSTEAD ACCUMULATE ONLY 0.25-0.5 INCHES. REGARDLESS OF THE OUTCOME,
IMPACTFUL FLOODING IS NOT EXPECTED. ANY LINGERING SHOWERS AND
THUNDERSTORMS WILL QUICKLY DISSIPATE FRIDAY EVENING/NIGHT AS HIGH
PRESSURE BUILDS IN BEHIND THE DEPARTING LOW PRESSURE SYSTEM. THIS
WILL SET THE STAGE FOR POTENTIAL AREAS OF FROST OVER THE UPPER HOOD
RIVER VALLEY FRIDAY NIGHT AS OVERNIGHT LOWS DIP INTO THE MID 30S NEAR
PARKDALE AND DEE (60-75% CHANCE FOR LOWS BELOW 37 DEGREES). -23
LONG TERM...SATURDAY THROUGH WEDNESDAY NIGHT
THE LONG TERM
FORECAST IS HIGHLIGHTED BY QUIETER FALL-LIKE WEATHER WITH SLIGHTLY
COOLER THAN NORMAL TEMPERATURES AND MAINLY DRY CONDITIONS. ON SUNDAY,
WPC'S CLUSTER ANALYSIS FOR 500 MB HEIGHTS AND ANOMALIES SHOWS
EXCELLENT AGREEMENT BETWEEN THE CANADIAN, GFS, AND EURO ENSEMBLES
WITH A WEAK TROUGH MOVING OVER THE PACIFIC NORTHWEST LATE SATURDAY
INTO SUNDAY. DESPITE THE INCOMING TROUGH, MOISTURE WILL BE LACKING,
AND GUIDANCE REMAINS IN GOOD AGREEMENT FOR DRY WEATHER SATURDAY
THROUGH SUNDAY. THE NBM BACKS THIS UP, AS PROBABILITIES FOR
PRECIPITATION ARE NEAR 0%. HOWEVER, THIS TROUGH WILL BRING SLIGHTLY
COOLER THAN AVERAGE TEMPERATURES FOR LATE SEPTEMBER WITH HIGHS IN THE
60S ACROSS THE LOWLANDS.
AS THE TROUGH MOVES EASTWARD EARLY NEXT WEEK, IT APPEARS WEAK
SHORTWAVE RIDGING WILL ATTEMPT TO DEVELOP ON THE BACKSIDE OF THE
TROUGH, BRINGING NEAR NORMAL UPPER LEVEL HEIGHTS TO NORTHWEST OREGON
AND SOUTHWEST WASHINGTON. IN RESPONSE, FORECAST TEMPERATURE INCREASE
A FEW DEGREES. A GLANCING SHORTWAVE TROUGH BEHIND THE SHORTWAVE RIDGE
WILL BRING LOW CHANCES FOR LIGHT RAIN FOR SOME AREAS ON TUESDAY,
MAINLY OVER SOUTHWEST WA AND ALONG THE COAST (15-35% CHANCE).
IT IS ALSO WORTH NOTING THAT CHANCES FOR FROST REMAIN IN THE FORECAST
OVER THE UPPER HOOD RIVER VALLEY SATURDAY MORNING THROUGH MONDAY
MORNING AS TEMPERATURES LIKELY DIP INTO THE 30S, ESPECIALLY NEAR
PARKDALE AND DEE. -23
AVIATION...THROUGH 12Z FRIDAY
WEST TO SOUTHWEST FLOW ALOFT
WILL TURN MORE SOUTHERLY THURSDAY AFTERNOON AS A LOW PRESSURE
SYSTEM APPROACHES THE REGION. HIGH CLOUDS CONTINUE TO INCREASE OVER
THE AREA THIS MORNING WITH PREDOMINATELY VFR CONDITIONS EXPECTED
THROUGH THURSDAY AFTERNOON. HOWEVER, THERE IS A LOW (15-25%) CHANCE
FOR MVFR CONDITIONS OR LOWER IN THE SOUTHERN WILLAMETTE VALLEY
BETWEEN 12-17Z THURSDAY WITH POTENTIAL PATCHY FOG/LOW STRATUS
DEVELOPMENT.
CONDITIONS WILL BECOME RAINY AND WINDY AS A FRONTAL BOUNDARY AHEAD OF
THE INCOMING LOW MOVES INLAND LATE TODAY, WITH RAIN LIKELY ARRIVING
AT THE COAST BY APPROXIMATELY 00Z FRIDAY AND AT INLAND TERMINALS BY
06-07Z FRIDAY. SOUTH WINDS WILL INCREASE SUBSTANTIALLY, LIKELY
REACHING 30-35 KT AT KAST OR STRONGER BY 10Z FRIDAY AND UPWARDS OF 40
KT AT KONP. GUSTS UP TO 25-30 KT ARE LIKELY OVER INLAND TERMINALS BY
THE END OF THE 12Z TAF CYCLE. WINDS INCREASE A BIT MORE AFTER 12Z
FRIDAY WITH SCATTERED SHOWERS EXPECTED THROUGH THE DAY FRIDAY. THERE
IS ALSO A 15-20% CHANCE OF ISOLATED THUNDERSTORMS FRIDAY AFTERNOON AT
ALL TERMINALS. STRONGER SHOWERS OR STORMS WILL HAVE THE POTENTIAL TO
PRODUCE GUSTY AND ERRATIC OUTFLOW WINDS UPWARDS OF 35-40 KT. LOW
LEVEL WIND SHEAR WILL ALSO BE ON THE INCREASED AFTER 12Z FRIDAY. -23
KPDX AND APPROACHES...VFR CONDITIONS WITH HIGH CLOUDS WILL CONTINUE
THROUGH THIS AFTERNOON. AN INCOMING FRONT WILL BRING RAIN AND
INCREASING SOUTH WINDS BY 06-07Z FRIDAY, WITH RAIN THEN CONTINUING
THROUGH FRIDAY MORNING AS WIND GUSTS INCREASE TO 25-30 KT. HEAVIER
SHOWERS AND POTENTIAL THUNDERSTORMS FRIDAY AFTERNOON COULD PRODUCE
OUTFLOW WIND GUSTS AS HIGH AS 35-40 KT. LOW LEVEL WIND SHEAR WILL
ALSO BE ON THE INCREASED AFTER 12Z FRIDAY. -23
MARINE
A STRONG LOW PRESSURE SYSTEM WILL MOVE OVER THE COASTAL
WATERS LATE THURSDAY INTO FRIDAY, BRINGING RAPIDLY INCREASING
WINDS AND SEAS ALONG WITH WIDESPREAD RAIN. GUIDANCE HAS COME INTO
BETTER AGREEMENT REGARDING THE STRENGTH AND TRACK OF THE LOW,
SUGGESTING THE LOW WILL COME IN STRONGER THAN WHAT WAS FAVORED
12-24+ HOURS AGO. CONFIDENCE IS NOW HIGH FOR WIDESPREAD GALE FORCE
WIND GUSTS OVER 34 KT ACROSS ALL OF THE COASTAL WATERS, INCLUDING THE
COLUMBIA RIVER BAR, AS PROBABILITIES FOR GALE FORCE WIND GUSTS
HAVE INCREASED TO 80-95%. IN FACT, WIND GUSTS WILL LIKELY PEAK AS
HIGH AS 40-45 KT ALONG THE SOUTH SIDE OF THE LOW (60-80% CHANCE).
BRIEF AND ISOLATED STORM FORCE WIND GUSTS UPWARDS OF 50 KT CANNOT
BE COMPLETELY RULED OUT NEAR THE LOW CENTER ON THE SOUTH SIDE (30-50%
CHANCE). THE HIGHEST PROBABILITIES FOR ISOLATED STORM FORCE WIND
GUSTS ARE OVER THE CENTRAL WATERS BETWEEN CAPE FALCON AND CAPE
FOULWEATHER.
GIVEN THE UPTICK IN FORECAST WIND SPEEDS, THE GALE WATCH HAS BEEN
UPGRADED TO A HIGH-END GALE WARNING FOR WIDESPREAD WIND GUSTS UP
TO 40-45 KT AND ISOLATED GUSTS AS HIGH AS 50 KT. WINDS WILL
INITIALLY START OUT SOUTHERLY THURSDAY NIGHT, THEN BECOME
SOUTHWESTERLY EARLY FRIDAY MORNING, THEN WESTERLY BY MID TO LATE
FRIDAY MORNING.
WITH THE RAPIDLY INCREASING WINDS THURSDAY EVENING/NIGHT, WAVE
HEIGHTS WILL INCREASE QUICKLY WITH SEAS BECOMING STEEP AND HAZARDOUS.
SEAS WILL MOST LIKELY PEAK SOMEWHERE BETWEEN 14 AND 17 FT FRIDAY
MORNING, BEGINNING AROUND SUNRISE. THERE IS A 10% CHANCE SEAS
COULD PEAK AS HIGH AS 20 FT WHERE THE BELT OF STRONGEST WINDS
OCCUR. SEAS OVER THE MAIN CHANNEL OF THE COLUMBIA RIVER BAR ARE
EXPECTED TO PEAK CLOSE TO 15 FT. GIVEN SEAS WILL BE MAINLY WIND
DRIVEN, WAVE HEIGHTS WILL FALL RAPIDLY FRIDAY EVENING/NIGHT AS
WINDS DECREASE. BY SUNRISE ON SATURDAY, SEAS SHOULD BE CLOSER TO 6
TO 7 FT. NORTHERLY WINDS INCREASE OVER THE WEEKEND, STRONGEST
SATURDAY AFTERNOON AND EVENING WHEN WIND GUSTS SHOULD INCREASE TO
20-25 KT. -23
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...GALE WARNING FROM 11 PM THIS EVENING TO 2 PM PDT FRIDAY FOR
PZZ210-251-252-271-272.
GALE WARNING FROM 8 PM THIS EVENING TO 11 AM PDT FRIDAY FOR
PZZ253-273.
WWW.WEATHER.GOV/PORTLAND
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