963
FXUS66 KPQR 171050
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
350 AM PDT THU SEP 17 2026
SYNOPSIS
TODAY WILL BE THE WARMEST DAY OF THE WEEK AS WEAK
OFFSHORE FLOW GIVES WAY TO ONSHORE FLOW DURING THE AFTERNOON. A
FEW SHOWERS AND AN ISOLATED THUNDERSTORM ARE POSSIBLE IN THE
LANE AND LINN COUNTY CASCADES, WHILE THE REMAINDER OF THE AREA
STAYS DRY. TEMPERATURES WARM AGAIN OVER THE WEEKEND BEFORE A
COOLER PATTERN BECOMES INCREASINGLY LIKELY EARLY NEXT WEEK.
DISCUSSION..NOW THROUGH WEDNESDAY
THE UPPER-LEVEL LOW OVER
NORTHERN CALIFORNIA WILL BEGIN SHIFTING NORTHEAST TOWARD THE
GREAT BASIN TODAY AS RIDGING BUILDS EASTWARD ACROSS THE PACIFIC
NORTHWEST. THIS WILL ALLOW THE SURFACE THERMAL TROUGH TO WEAKEN
THROUGH THE DAY, BUT NOT BEFORE ANOTHER WARM AFTERNOON ACROSS
THE INTERIOR LOWLANDS. HIGHS ARE EXPECTED TO REACH THE LOW TO
MID 80S, WITH THE WARMEST READINGS FROM THE PORTLAND METRO
TO CORVALLIS. THERE IS A 30-70% PROBABILITY OF TEMPERATURES
REACHING 85 DEGREES OR HIGHER FROM THE PORTLAND METRO TO
CORVALLIS, WITH THE HIGHEST CHANCES IN THE TUALATIN VALLEY. AS
FOR 90 DEGREES OR HIGHER, ONLY A 10-20% CHANCE IN THE TUALATIN
VALLEY AND LESS THAN 5% ELSEWHERE. AREAS SOUTH OF CORVALLIS
SHOULD REMAIN MAINLY IN THE LOW 80S, WHILE COASTAL AND HIGHER
TERRAIN LOCATIONS STAY CONSIDERABLY COOLER WITH HIGHS IN THE
UPPER 60S TO MID 70S.
OFFSHORE FLOW WILL LINGER THROUGH THE MORNING, PARTICULARLY
ACROSS THE CASCADES, FOOTHILLS AND WESTERN COLUMBIA RIVER GORGE,
BEFORE THE THERMAL TROUGH BREAKS DOWN AND ONSHORE FLOW RETURNS
THIS AFTERNOON. NORTHERLY WINDS WILL CONTINUE ELSEWHERE, WITH
BREEZY CONDITIONS POSSIBLE THROUGH THE MORNING BEFORE THE WIND
PATTERN GRADUALLY BECOMES MORE WESTERLY. THE RETURN OF ONSHORE
FLOW SHOULD ALSO HELP MODERATE TEMPERATURES LATER IN THE DAY,
PARTICULARLY CLOSER TO THE COAST.
THE UPPER LOW'S NORTHEASTWARD MOVEMENT WILL BRING A MODEST
INCREASE IN MOISTURE INTO THE SOUTHERN CASCADES TODAY. AS A
RESULT, SHOWER CHANCES INCREASE ACROSS THE LANE AND LINN COUNTY
CASCADES, WITH PROBABILITIES REACHING 20-60%. A STRAY
THUNDERSTORM CANNOT BE RULED OUT, WITH AROUND A 10% CHANCE ALONG
THE HIGHER TERRAIN. THE REMAINDER OF THE FORECAST AREA IS
EXPECTED TO REMAIN DRY, WITH LITTLE SUPPORT FOR CONVECTION
ELSEWHERE.
FRIDAY MARKS A RETURN TO A MORE TYPICAL ONSHORE-FLOW PATTERN,
WITH MARINE STRATUS LIKELY DEVELOPING ALONG THE COAST AND
SPREADING INTO PORTIONS OF THE INTERIOR LOWLANDS DURING THE
MORNING, SUCH AS THROUGH THE COASTAL GAPS AND UP THE COLUMBIA
RIVER. TEMPERATURES WILL DEPEND IN PART ON HOW QUICKLY THE LOW
CLOUDS ERODE, AS WELL AS THE EVOLVING UPPER-LEVEL PATTERN.
ENSEMBLE GUIDANCE STILL SHOWS SOME SPREAD, WITH A COOLER OUTCOME
FAVORING INTERIOR HIGHS IN THE LOWER 70S AND WARMER SOLUTIONS
SUPPORTING UPPER 70S TO POSSIBLY 80. REGARDLESS, PRECIPITATION
CHANCES REMAIN LOW AND CONDITIONS SHOULD STAY DRY ACROSS THE
AREA.
FORECAST CONFIDENCE IMPROVES SLIGHTLY HEADING INTO THE WEEKEND,
WITH TEMPERATURES EXPECTED TO CLIMB INTO THE MID 70S TO LOW 80S
SATURDAY AND MID 70S TO UPPER 80S SUNDAY UNDER GENERALLY DRY
CONDITIONS. ATTENTION THEN TURNS TOWARD A DEVELOPING TROUGH
DROPPING SOUTH FROM THE GULF OF ALASKA EARLY NEXT WEEK. THERE
REMAINS CONSIDERABLE UNCERTAINTY IN THE EVENTUAL STRENGTH,
POSITION AND TIMING OF THIS FEATURE, BUT THE OVERALL PATTERN
INCREASINGLY FAVORS COOLER TEMPERATURES AND STRONGER ONSHORE
FLOW. AT THIS TIME, THERE IS AROUND A 20% CHANCE FOR MEASURABLE
RAINFALL TUESDAY THROUGH WEDNESDAY ACROSS SOUTHWEST WASHINGTON
AND NORTHWEST OREGON, BUT AGAIN, MUCH OF THE FORECAST BEYOND THE
WEEKEND REMAINS UNCERTAIN. ~12
AVIATION...THROUGH 12Z FRIDAY
EAST TO NORTHEAST FLOW ALOFT
CONTINUES THROUGH MOST OF THE TAF PERIOD AS AN UPPER LEVEL LOW
OVER NORTHERN CALIFORNIA BEGINS TO HEAD NORTHEAST. EXPECT VFR
CONDITIONS AT INLAND TERMINALS THROUGH MOST OF THE PERIOD, WITH
A 10-30% CHANCE OF MVFR CIGS FROM 06-12Z FRI. THESE CHANCES WILL
CONTINUE TO INCREASE AS MARINE STRATUS IS INCREASINGLY LIKELY TO
PUSH INLAND THURSDAY NIGHT. AT THE COAST, THERE IS A 30-40%
CHANCE OF IFR AND 20-30% CHANCE OF LIFR CONDITIONS UNTIL 17-18Z
THU. COASTAL CONDITIONS THEN IMPROVE BACK TO VFR BY 19Z THU
(80-90% CHANCE OF VFR). BETWEEN 00-12Z FRI, THE RETURN OF
ONSHORE WINDS WILL BRING CHANCES FOR DETERIORATED CONDITIONS AT
THE COASTAL, AROUND 70-90% FOR MVFR, 30-40% FOR IFR, AND 10-20%
FOR LIFR (HIGHEST CHANCES BETWEEN 6-12Z FRI AT KAST AND 00-06Z
FRI AT KONP). OTHERWISE, LIGHT WINDS THIS MORNING WILL INCREASE
TO 5-10 KT DURING THE AFTERNOON, WITH RATHER LOW CONFIDENCE IN
WIND DIRECTION. MOST TERMINALS LOOK TO SHIFT FROM NORTHWESTERLY
TO SOUTHERLY THROUGH THE PERIOD.
KPDX AND APPROACHES...VFR CONDITIONS EXPECTED THROUGH MOST OF THE
TAF PERIOD WITH MOSTLY CLEAR SKIES, THEN A 10-30% OF MVFR CIGS
AFTER 06Z FRI AS MARINE STRATUS ATTEMPTS TO PUSH INLAND.
NORTHWEST TO WESTERLY WINDS AROUND 4-6 KT THROUGH MOST OF THE
PERIOD, THEN SHIFTING SOUTHERLY BY 07-09Z FRI. ~12
MARINE
NORTH WINDS EASE TODAY AND SHIFT MORE WEST TO
SOUTHWEST OVER THE WATERS ABOUT 40-50 NM FROM THE COAST TONIGHT
INTO FRIDAY. A PERSISTENT NORTHWEST SWELL AROUND 4 TO 6 FT AT 7
TO 8 SECONDS IS EXPECTED TO CONTINUE THROUGH AT LEAST SUNDAY.
NORTHERLIES STRENGTHEN AGAIN OVER THE WEEKEND. THE WATERS SOUTH
OF CAPE FALCON HAVE AROUND A 50-80% CHANCE OF AT LEAST
OCCASIONAL WIND GUSTS EXCEEDING 21 KT. THE WATERS NORTH OF CAPE
FALCON HAVE A 15-30% CHANCE OF WIND GUSTS EXCEEDING 21 KT ON
SATURDAY, INCREASING TO 50-70% BY SUNDAY. THERE IS THEN A 50/50
CHANCE OF CONTINUED SMALL CRAFT WINDS INTO EARLY NEXT WEEK. A
NORTH TO NORTHWEST SWELL OF 5 TO 7 FT AT 8 TO 10 SECONDS ARRIVES
EARLY NEXT WEEK. ~12/03
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