635
FXUS66 KPQR 102221
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
321 PM PDT WED SEP 10 2025
SYNOPSIS
CONDITIONS TREND DRIER THE NEXT SEVERAL DAYS AS
LINGERING SHOWER AND THUNDERSTORM CHANCES (PRIMARILY OVER THE
OREGON CASCADES) BEGIN TO DWINDLE. EXPECT A BRIEF WARM-UP FOR
THE FIRST HALF OF THE WEEKEND. WHILE THE FORECAST BECOMES MORE
UNCERTAIN SUNDAY ONWARD, ESPECIALLY BY THE MIDDLE OF NEXT WEEK,
COOLER AND WETTER WEATHER SUNDAY INTO MONDAY IS FAVORED WITH A
50-70% CHANCE FOR RAINFALL.
DISCUSSION...NOW THROUGH TUESDAY NIGHT
AN UPPER-LEVEL LOW
CONTINUES TO CHURN OVER NORTHERN CALIFORNIA AND FAR SOUTHERN
OREGON THIS AFTERNOON REMAINING THE PRIMARY DRIVER OF IMPACTS
FOR THE NEXT DAY OR TWO. CURRENT SATELLITE AND RADAR
OBSERVATIONS DEPICT SHOWERS AND THUNDERSTORMS DEVELOPING OVER
THE OREGON AND WASHINGTON CASCADES AS OF 1400-1500 TODAY THANKS
TO SOME DIURNAL HEATING ALONG THE CRESTS AND THE INFLUENCE OF
THAT AFOREMENTIONED UPPER-LEVEL LOW JUST TO OUR SOUTH. MODEL
SOUNDINGS SHOW A FAIRLY DEEP BUT "THIN" CAPE PROFILE
(~500-1000J/KG) IN ADDITION TO ENE STEERING FLOW SO WHILE THE
CHANCE FOR ANY STRONG SEVERE THUNDERSTORMS ARE VERY LOW (<5%),
OCCASIONAL LIGHTNING, SMALL HAIL, GUSTY OUTFLOW WINDS, AND
LOCALLY HEAVY RAIN ARE ALL POSSIBLE IMPACTS FROM THUNDERSTORMS
TODAY. THIS LATTER POINT REGRADING HEAVY RAINFALL SHOULD BE
EMPHASIZED TOO, AS THE THIN VERTICAL CAPE PROFILE MIXED WITH
PWAT VALUES NEAR 1.2-1.3" AND SLOW STORM MOTION WILL LEAD TO
EFFICIENT RAINFALL PRODUCTION - MUCH LIKE THE ACTIVITY
YESTERDAY. WHILE THUNDERSTORMS LIKELY WANDER EAST TO WEST TOWARDS
THE CASCADES FOOTHILL AREAS AS THE AFTERNOON AND EVENING
PROGRESS, IT'S UNLIKELY THEY'LL MAINTAIN ENOUGH STRENGTH TO BE
OF ANY THREAT TO THE I-5 CORRIDOR. THIS IS DUE IN-PART TO THE
MARINE AIRMASS IN PLACE PLACE ACROSS THE LOWER ELEVATIONS WHICH
HAS BEEN SLUGGISH TO CLEAR TODAY.
CHANCES FOR SHOWERS AND THUNDERSTORMS WILL CONTINUE FOR THE
CASCADES WEDNESDAY NIGHT THROUGH THURSDAY AS A SLOW-MOVING UPPER
LEVEL LOW PRESSURE SYSTEM GRADUALLY SHIFTS INTO NORTHERN
NEVADA, EASTERN OREGON AND IDAHO, WHILE CONTINUING TO SWING
WRAP-AROUND MOISTURE TO THE AREA. MEANWHILE, DRY WEATHER AND
MILD TEMPERATURES WILL CONTINUE WEST OF THE CASCADES WITH
CONDITIONS ON THURSDAY VERY SIMILAR TODAY. ALL IN ALL,
THUNDERSTORM CHANCES ON THURSDAY APPEAR MORE CONFINED TO THE
CASCADE CRESTS COMPARED TO PAST DAYS WITH SIMILAR IMPACTS.
BY FRIDAY, MODELS AND THEIR ENSEMBLES REMAIN IN EXCELLENT
AGREEMENT SHOWING A SHORTWAVE RIDGE PUSHING INTO WESTERN WA/OR
FROM THE WEST, ON THE BACKSIDE OF THE PREVIOUSLY MENTIONED LOW
PRESSURE SYSTEM. THIS RIDGE WILL BRING DRY WEATHER ACROSS THE
REGION WITH WARMING TEMPERATURES ON FRIDAY AND SATURDAY. EXPECT
MORNING CLOUD COVER IN THE LOWLANDS AND AFTERNOON SUN BOTH
DAYS, WITH HIGH TEMPERATURES IN THE UPPER 70S TO LOWER 80S FOR
INLAND VALLEYS, AND UPPER 60S AT THE COAST - NEAR NORMAL FOR
THIS TIME OF YEAR. ONE IT REMAINS TO BE SEEN HOW QUICKLY THE
MORNING MARINE LAYER AND ACCOMPANYING LOW CLOUDS WILL MIX OUT AS
MODELS ARE OFTEN TOO ENTHUSIASTIC WITH THEIR BOUNDARY LAYER
MIXING, BUT A WEAK OFFSHORE COMPONENT TO THE LOW-LEVEL FLOW
SHOULD HELP WITH THE PROCESS AT LEAST ON SATURDAY.
FORECAST CONFIDENCE BEGINS TO LOWER ON SUNDAY AS MODELS
STRUGGLE TO RESOLVE THE EVOLUTION OF AN UPPER LEVEL TROUGH THAT
WILL MOVE TOWARDS THE PACIFIC NORTHWEST FROM THE NORTHEAST
PACIFIC. A PORTION (25-30%) OF ENSEMBLE GUIDANCE SUGGESTS THIS
TROUGH WILL SLOW DOWN BEFORE MAKING LANDFALL AND FORM A CLOSED
CUT-OFF LOW THAT DIVES SOUTHEASTWARD INTO NORTHERN CALIFORNIA
AND STALLS. THIS SCENARIO WOULD RESULT IN LITTLE RAIN FOR THE
INLAND VALLEYS, WARMER TEMPERATURES SUNDAY INTO EARLY NEXT
WEEK, AND MORE CASCADE THUNDERSTORM CHANCES. HOWEVER, THIS
SCENARIO IS LOOKING INCREASINGLY UNLIKELY GIVEN THE LATEST 12Z
MODEL GUIDANCE. THE MAJORITY OF ENSEMBLE GUIDANCE (70-75%) ON
THE OTHER HAND DEPICT THE TROUGH MOVING DIRECTLY INTO WESTERN
WA/OR AS EITHER AN OPEN WAVE OR CLOSE LOW. THIS SCENARIO WOULD
BRING WIDESPREAD RAIN TO THE AREA AND SOMEWHAT COOLER
TEMPERATURES SUNDAY INTO EARLY NEXT WEEK. PROBABILITIES ARE
SHIFTING IN FAVOR THE COOLER AND WETTER SCENARIO, AND QPF PLUMES
FROM THE ENS/GEFS/GEPS ENSEMBLES ALL SHOW ENSEMBLE MEMBER
CLUSTERING BETWEEN A 0.1-0.4 INCHES FOR QPF AMOUNTS. THAT SAID,
THERE IS STILL A FAIR AMOUNT OF RUN TO RUN MODEL VARIABILITY.
MODEL UNCERTAINTY STAYS ELEVATED FOR THE THE MIDDLE OF NEXT WEEK
AS DETERMINISTIC AND ENSEMBLE SYSTEMS STRUGGLE TO RESOLVE OF
THE UPPER-LEVEL LOW/TROUGH PROGRESSION TO THE EAST AND THE
POTENTIAL DEVELOPMENT OF ANOTHER TROUGH FEATURE OVER THE EASTERN
PACIFIC.-SCHULDT/TK
AVIATION
MVFR CIGS PERSIST ACROSS PORTIONS OF THE AREA WITH THE
THICKEST CLOUD COVER ALONG THE COAST. CLOUD COVER HAS BROKEN UP A
BIT INLAND LEADING TO SOME VFR CONDITIONS IN THE WILLAMETTE
VALLEY. WINDS OUT OF THE NORTH/NORTHWEST AT 5-10 KT THROUGH THE
DAY. EXPECTING MARINE STRATUS TO PERSIST ALONG THE COAST AGAIN
WITH GUIDANCE SUGGESTING STRATUS PUSHING INLAND BETWEEN 10-12Z
THU, BRINGING MVFR CIGS TO MUCH OF THE WILLAMETTE VALLEY.
LOW PRESSURE IS FAR ENOUGH SOUTH TO KEEP CONDITIONS MAINLY DRY
TODAY, HOWEVER, A 15-30% CHANCE FOR SHOWERS AND THUNDERSTORMS
REMAINS FOR THE CASCADES AND CASCADE FOOTHILLS THROUGH 03Z THU.
THERE IS LESS THAN 10% CHANCE THAT A THUNDERSTORM MOVES WESTWARD
INTO THE WILLAMETTE VALLEY, BUT COULD SEE A STRAY SHOWER OR TWO
OVER KEUG.
KPDX AND APPROACHES...MVFR CIGS CONTINUE TO HOLD BUT SATELLITE
IMAGERY SHOWS CLOUDS DISSIPATING AROUND THE METRO. VFR CONDITIONS
EXPECTED LATE THIS AFTERNOON WITH NORTHERLY WINDS AROUND 5 KT
EXPECTED THROUGH EARLY TONIGHT. ANOTHER MARINE PUSH IS EXPECTED TO
BRING MVFR (POSSIBLY IFR) CIGS BETWEEN 10-12Z THU. -BATZ/ALVIZ
MARINE
HIGH PRESSURE OVER THE WATERS WILL MAINTAIN NORTHERLY
TO NORTHWESTERLY WINDS WITH GUSTS LESS THAN 15 KT THROUGH
THURSDAY. WINDS BECOME MORE VARIABLE ACROSS THE WATERS ON FRIDAY
AHEAD OF THE NEXT SYSTEM, BUT STILL REMAIN LIGHT. EXPECT SEAS
TO BUILD TO 5-6 FT AT 13-14 SEC THURSDAY TO FRIDAY WITH A WEST-
NORTHWESTERLY SWELL.
HEADING INTO THE WEEKEND, ANOTHER LOW PRESSURE SYSTEM IN THE
NORTHEAST PACIFIC WILL APPROACH THE PACIFIC NORTHWEST. A FRONT
ASSOCIATED WITH THIS LOW WILL WEAKEN AS IT MOVES ACROSS THE WATERS
SATURDAY AND SUNDAY. THE WINDS WILL SHIFT SOUTHERLY AHEAD OF THE
FRONT ON SATURDAY, THEN NORTHERLY WITH AND BEHIND THE FRONT BY
SUNDAY AFTERNOON. PROBABILITIES FOR OBSERVING WIND GUSTS OF 21 KT
OR GREATER (SMALL CRAFT CONDITIONS) ACROSS THE WATERS IN A 24 HOUR
PERIOD ON SATURDAY RANGE FROM 30-50%, HIGHEST ACROSS THE OUTER
WATERS. PROBABILITIES INCREASE SUNDAY TO 50-70% FOR ALL MARINE
ZONES. HOWEVER, 1-HOUR PROBABILITIES FOR SMALL CRAFT GUSTS ARE
ONLY 10-15%, SUGGESTING THAT ANY SMALL CRAFT WIND GUSTS MAY BE
BRIEF AND NOT AS FREQUENT/LONG-LASTING. GIVEN THE LEAD TIME AND
SOME UNCERTAINTY WITH THE EXACT LOW TRACK, WILL HOLD OFF ON
ISSUING ANY PRODUCTS FOR NOW. 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 9-12 FEET AT
10-12 SECONDS WHICH WOULD SUPPORT STEEP, HAZARDOUS SEAS FOR SOME
TIME. -BATZ/ALVIZ
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 5 PM THIS AFTERNOON TO 10 PM PDT
THIS EVENING FOR PZZ210.
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