830
FXUS66 KPQR 112219
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
319 PM PDT THU SEP 11 2025
SYNOPSIS
EXPECT A GRADUAL TRANSITION TO WARMER CONDITIONS AND
SUNNIER SKIES THROUGH THE FIRST HALF OF THE WEEKEND. THEN, OUR
NEXT FRONTAL SYSTEM ARRIVES LATER SATURDAY NIGHT TO SUNDAY
USHERING IN A PERIOD OF WIDESPREAD LIGHT RAIN. CONDITIONS DRY
AND WARM UP AGAIN EARLY NEXT WEEK WITH THE POTENTIAL FOR
OFFSHORE WINDS ON TUESDAY.
SHORT TERM...NOW THROUGH SATURDAY NIGHT
THIS AFTERNOON
SATELLITE IMAGERY SHOWS WIDESPREAD STRATUS JUST BEGINNING
TO BREAK UP ACROSS THE WILLAMETTE VALLEY AS WESTERLY FLOW AND
DEEP MARINE INFLUENCE DOMINATE THE PATTERN NEAR THE SURFACE.
ALOFT, THE UPPER-LEVEL LOW WHICH HAS FACILITATED SEVERAL ROUNDS
OF SHOWERS AND THUNDERSTORMS OVER THE REGION THE THE LAST
SEVERAL DAYS HAS FINALLY PROGRESSED INTO NORTHERN NEVADA KEEPING
THE COVERAGE OF ANY ACTIVITY FAIRLY LIMITED TO THE OREGON
CASACDES INTO THE EVENING HOURS BEFORE DRY WEATHER RETURNS.
WHILE THE STORM MOTION WILL HAVE A SLIGHT EASTERLY COMPONENT
(NNE TO SSW), THE AFOREMENTIONED MARINE LAYER JUST WEST OF THE
CRESTS WILL ENSURE STORMS WEAKEN AND DECAY IF/WHEN THEY SHIFT
OFF THE CRESTS.
STARTING TOMORROW (FRIDAY) A TRANSIENT SHORTWAVE RIDGE WHICH AS
BEEN HOLDING OVER THE EASTERN PACIFIC BEGINS TO SHIFT OVERHEAD
LEADING TO A THINNER DECK OF MORNING LOW CLOUDS INLAND AND
GENERALLY SUNNIER SKIES BY THE AFTERNOON HOURS. DUE TO THE MORE
EXPEDIENT CLEARING, HIGHS LIKELY JUMP INTO THE MID 70S AROUND
THE PORTLAND/VANCOUVER METRO AND MID TO UPPER 70S CENTRAL AND
SOUTH WILLAMETTE VALLEY. THE AXIS OF THE HIGH PRESSURE RIDGE
PASSES OVERHEAD ON SATURDAY WHICH WILL ALMOST CERTAINLY END UP A
THE WARMEST DAY OF THE NEXT ~4-5 DAYS OR SO - TEMPERATURES PEAK
IN THE UPPER 70S TO LOW 80S WILLAMETTE VALLEY AND CASCADE
VALLEYS. HOWEVER, SATURDAY EVENING CLOUDS BEGIN TO INCREASE FROM
THE WEST THANKS TO AN APPROACHING FRONTAL BOUNDARY SLATED TO
BRING AT LEAST LIGHT WIDESPREAD RAINFALL TO THE REGION FOR THE
LATTER HALF OF THE WEEKEND. -SCHULDT
LONG TERM...SUNDAY THROUGH THURSDAY
WIDESPREAD RAIN RETURNS
ACROSS NORTHWEST OREGON AND SOUTHWEST WASHINGTON AS OUR FIRST
FALL-LIKE FRONTAL SYSTEM SWINGS THROUGH THE REGION. ENSEMBLE
GUIDANCE SYSTEMS(ENS/GEFS/GEPS) ARE IN GENERAL AGREEMENT (80%
CHANCE) THAT THE FRONT WILL MOVE THROUGH LATE SATURDAY NIGHT
INTO SUNDAY MORNING, WHICH IS WHEN THE BULK OF THE RAIN IS
EXPECTED. THE LATEST 12 NAM STILL APPEARS TO BE AN OUTLIER
PUSHING THE BULK OF THE ENERGY WITH THIS FRONT FURTHER SOUTH
INTO SOUTHERN OREGON AND NORTHERN CALIFORNIA. IF THIS SCENARIO
WERE TO OCCUR, THEN WE WOULD END UP MUCH DRIER THAN FORECASTED.
WHILE THE ENSEMBLE MODELS ARE IN GENERAL AGREEMENT WITH THE
TIMING OF THE FRONT, THERE IS STILL UNCERTAINTY WITH THE
MAGNITUDE OF THE FRONT, AND THUS TOTAL RAINFALL AMOUNTS. THE NBM
75TH PERCENTILE FOR 24 HOUR RAINFALL ENDING 5 PM SUNDAY IS
AROUND 1.2-1.5" ALONG THE COAST AND 0.50-0.80" ACROSS INTERIOR
VALLEYS, WHILE THE NBM 25TH PERCENTILE IS AROUND 0.30-0.50"
ALONG THE COAST AND 0.05-0.20" ACROSS INTERIOR VALLEYS.
CURRENTLY, THE GEFS ENSEMBLE IS WANTING TO BRING IN THE HIGHER-
END RAINFALL AMOUNTS WHILE THE ENS/GEPS ENSEMBLES ARE SUGGESTING
LOWER AMOUNTS. WILL CONTINUE TO MONITOR HOW THIS EVOLVES IN THE
NEXT DAY OR SO. FOR NOW, WE CAN GENERALLY SAY THAT SUNDAY IS
LOOKING TO BE WETTER AND COOLER. BY LATE SUNDAY AFTERNOON, THE
FRONT WILL WEAKEN AND RAIN WILL GRADUALLY TAPER OFF SUNDAY NIGHT
INTO EARLY MONDAY MORNING.
THE SECOND HALF OF MONDAY LOOKS DRIER AS SHORTWAVE RIDGING
RETURNS IN EARNEST AND THE AFOREMENTIONED SYSTEM PROGRESSES
EASTWARD. BY TUESDAY, THERE IS HIGH AGREEMENT AMONG ENSEMBLE
MEMBERS THAT ABOVE- AVERAGE 500 MB HEIGHTS RETURN, REBOUNDING
TEMPERATURES INTO THE LOW 80S ACROSS INTERIOR VALLEYS WITH SUNNY
SKIES. WEDNESDAY LOOKS SIMILAR TO TUESDAY, HOWEVER, A DECENT
SUBSET OF ENSEMBLE MEMBERS (~40%) DO ALSO SHOW A WEAK FRONT
APPROACHING THE PACIFIC NORTHWEST.
IT'S WORTH HIGHLIGHTING LATE MONDAY NIGHT THROUGH TUESDAY INTO
WEDNESDAY A THERMAL TROUGH DEVELOPS ACROSS WESTERN OREGON WITH
HIGH PRESSURE EAST OF THE CASCADES, LEADING TO AN OFFSHORE FLOW
PATTERN. THERE REMAINS SOME UNCERTAINTY IN THE EXACT PLACEMENT
OF THIS FEATURE WHICH WILL HELP TO MODULATE THE STRENGTH OF
OFFSHORE WINDS BUT FOR NOW THEY DON'T APPEAR PARTICULARLY
STRONG. THIS WILL BE A PERIOD TO MONITOR IN THE COMING DAYS.
-SCHULDT/ALVIZ
AVIATION
PREDOMINATELY MVFR CONDITIONS PERSIST ACROSS THE AREA
WITH MINIMAL DISSIPATION INDICATED ON SATELLITE. EXPECTING MVFR
CIGS TO PERSIST ACROSS MUCH OF THE AREA AS GUIDANCE POORLY
HANDLES THE MARINE LAYER, THOUGH A BRIEF BREAK IN THE CLOUDS IS
POSSIBLE AROUND 23Z THU TO 02Z FRI. MODEL SOUNDINGS ARE
INDICATING THIS CLOUD LAYER PERSISTING THROUGH THE NIGHT OVER THE
METRO AND NORTHERN WILLAMETTE VALLEY. IF STRATUS DOES DISSIPATE
INLAND, EXPECT IT TO REDEVELOP BETWEEN 10-12Z FRI. WINDS REMAIN
LIGHT AND VARIABLE, GENERALLY LESS THAN 10 KTS.
THERE REMAINS A 10-20% CHANCE FOR A STRAY SHOWER OVER THE CASCADES
AND CASCADE FOOTHILLS THROUGH 06Z FRI.
KPDX AND APPROACHES...MVFR CONDITIONS HOLDING STEADY BUT THE CLOUD
DECK SEEMS TO BE RISING SLOWLY. A BRIEF BREAK IN THE CLOUDS
REMAINS POSSIBLE LATE THIS EVENING. IF STRATUS DOES DISSIPATE, IT
IS EXPECTED TO REDEVELOP AROUND 10-12Z FRI. WEST TO NORTHWESTERLY
WINDS LESS THAN 10 KTS. -BATZ
MARINE
HIGH PRESSURE REMAINS IN PLACE OVER THE WATERS THROUGH
FRIDAY MORNING. WINDS OUT OF THE NORTHWEST AT 10 KTS OR LESS AND
WIND GUSTS BELOW 15 KT. WINDS BECOME MORE VARIABLE DURING THE
LATTER HALF OF FRIDAY AS A COLD FRONT BEGINS TO MOVE CLOSER TO THE
REGION. SEAS 5-6 FT AT 12-14 SECONDS THROUGH FRIDAY.
AN APPROACHING LOW PRESSURE SYSTEM WILL BRING THE AFOREMENTIONED
COLD FRONT TOWARD THE PACNW COAST, SHIFTING WINDS FROM
NORTHWESTERLY TO SOUTHERLY ON SATURDAY. PROBABILITIES FOR WIND
GUSTS OF 21 KT OR GREATER (SMALL CRAFT ADVISORY CRITERIA) ARE
50-70% WHEN LOOKING AT 24 HOUR PERIODS FOR SATURDAY AND SUNDAY.
HOWEVER, WHEN LOOKING CLOSER AT THE HOURLY PROBABILITIES, CHANCES
DROP SIGNIFICANTLY TO 10-30% AT THE HIGHEST ON EITHER DAY. THIS
INDICATES THAT SMALL CRAFT GUSTS ARE DEFINITELY POSSIBLE BUT
LIKELY WON'T BE WIDESPREAD OR LONG DURATION. STILL SOMETHING TO
WATCH IN CASE THE TRACK OF THE LOW CHANGES AND CONFIDENCE
INCREASES WHICH WOULD WARRANT A SHORT SMALL CRAFT ADVISORY. SEAS
ARE FORECAST AROUND 6-7 FEET AT 10-12 SEC THROUGH SATURDAY. A
NORTHWEST SWELL IS EXPECTED TO MOVE INTO THE WATERS ON SUNDAY
BRINGING WAVES OF 8-10 FEET AT 10-12 SECONDS WHICH WOULD SUPPORT
STEEP, HAZARDOUS SEAS FOR SOME TIME. -BATZ
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...NONE.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSPORTLAND
X.COM/NWSPORTLAND
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page