646
FXUS66 KPQR 110405 AAA
AFDPQR
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PORTLAND OR
905 PM PDT WED SEP 10 2025
UPDATED AVIATION DISCUSSION
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
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/IFR CONDITIONS EXPECTED ALONG THE COAST THROUGH
THE TAF PERIOD. PREDOMINATELY MVFR CONDITIONS EXPECTED ALONG THE
COAST FROM 16Z THURSDAY THROUGH 03Z FRIDAY. FOR INLAND LOCATIONS
THE CURRENT VFR CONDITIONS ARE EXPECTED TO DETERIORATE TOWARDS
PREDOMINATELY MVFR, WHICH IS EXPECTED TO START AROUND 10Z-12Z
THURSDAY. THERE IS ALSO A 10-20% PROBABILITY OF POCKETS OF IFR
CONDITIONS WITHIN THE WILLAMETTE VALLEY, WITH HIGHER PROBABILITIES
OF THESE LOWERED FLIGHT CONDITIONS SOUTH OF KSLE. LOWERED FLIGHT
CONDITIONS INLAND ARE EXPECTED TO IMPROVE TOWARDS PREDOMINATELY
VFR AROUND 20Z-22Z THURSDAY.
THERE REMAINS A 15-30% PROBABILITY FOR SHOWERS AND A 10-20%
PROBABILITY FOR THUNDERSTORMS REMAINS FOR THE CASCADES AND CASCADE
FOOTHILLS THROUGH 06Z FRIDAY. THERE IS LESS THAN 10% PROBABILITY
THAT A THUNDERSTORM MOVES WESTWARD INTO THE WILLAMETTE VALLEY.
KPDX AND APPROACHES...CURRENT VFR CONDITIONS ARE EXPECTED TO LOWER
TOWARDS MVFR, WITH PREDOMINATELY MVFR CONDITIONS EXPECTED AROUND
10Z-12Z THURSDAY. ANY LOWERED FLIGHT CONDITIONS ARE EXPECTED TO
IMPROVE TOWARDS VFR STARTING AROUND 20Z THURSDAY. /42
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...NONE.
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