576
FXUS66 KPQR 171807 AAA
AFDPQR
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PORTLAND OR
1106 AM PDT THU SEP 17 2026
..UPDATED AVIATION DISCUSSION
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 18Z FRIDAY
SATELLITE IMAGERY AND TERMINAL
OBSERVATIONS AS OF LATE THURSDAY MORNING DEPICTS PREDOMINATELY VFR
CONDITIONS WITH MOSTLY SUNNY SKIES ACROSS THE NORTHERN OREGON COAST
AND WILLAMETTE VALLEY. AN EXCEPTION IS THE CENTRAL OREGON COAST
INCLUDING KONP, WHERE MARINE STRATUS HAS MOVED IN AND IS BRINGING
MVFR VIS AND IFR CIGS. HIGH CONFIDENCE (>80% CHANCE) THAT MARINE
STRATUS WILL GRADUALLY MAKE ITS WAY NORTHWARD AND REACH KAST BY 03-
06Z FRI. SOME THUNDERSTORM ACTIVITY OVER CENTRAL OREGON TODAY MAY
BRING SOME HIGH LEVEL CLOUDS OVER THE VALLEY, BUT THUNDERSTORMS ARE
NOT EXPECTED WEST OF THE CASCADE CREST (5% CHANCE OR LESS).
BY EARLY FRIDAY MORNING AROUND 10-12Z FRI, MARINE STRATUS WILL MOVE
UP THE LOWER COLUMBIA RIVER VALLEY AND GAPS THROUGH THE COAST RANGE
AND ENTER THE WILLAMETTE VALLEY. THERE IS A 40-60% CHANCE AT ANY
GIVEN HOUR BETWEEN 12-18Z FRI FOR MVFR CIGS (2-3 KFT) ACROSS VALLEY
TERMINALS, WITH THE HIGHEST CHANCES AT KEUG. WEST/SOUTHWEST WINDS
GENERALLY UNDER 10 KT FOR MOST LOCATIONS EXCEPT 9-12 KT AT KEUG
BETWEEN 21Z THU-06Z FRI.
KPDX AND APPROACHES...VFR CONDITIONS WITH MOSTLY CLEAR SKIES THROUGH
LATE THIS EVENING. 40-60% CHANCE FOR MVFR CIGS AT ANY GIVEN HOUR
BETWEEN 12-18Z FRI. NORTHWEST WINDS 4-5 KT TODAY TURNING SOUTHEAST
UNDER 5 KT OVERNIGHT. -10
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
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