518
FXUS66 KPQR 311755
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
1055 AM PDT MON AUG 31 2026
UPDATED AVIATION DISCUSSION.
SYNOPSIS
HIGH PRESSURE WILL RESULT IN DRY AND WARM
CONDITIONS ACROSS THE AREA TODAY. A SIGNIFICANT PATTERN CHANGE
BEGINS ON TUESDAY WITH A RETURN OF COOLER TEMPERATURES, RAIN,
AND BREEZY SOUTHERLY WINDS THROUGH THE END OF THE WEEK.
WEDNESDAY AND THURSDAY ARE EXPECTED TO BE THE WETTEST DAYS WITH
ALSO A 10-20% CHANCE FOR THUNDERSTORMS IN THE AFTERNOON.
CONDITIONS TREND SLIGHTLY DRIER OVER THE WEEKEND, BUT THERE
REMAINS CHANCES FOR LINGERING SHOWERS.
SHORT TERM...TODAY THROUGH TUESDAY NIGHT
DRY AND WARM
CONDITIONS CONTINUE TODAY AS SHORTWAVE RIDGING SETS UP OVER THE
PACIFIC NORTHWEST. EXPECT DAYTIME HIGHS IN THE MID TO UPPER 80S
ACROSS INTERIOR VALLEYS, UPPER 60S TO MID 70S ALONG THE COAST
AND MID 70S TO MID 80S FOR THE CASCADES. THIS DRY AND WARM
WEATHER WILL BE SHORT-LIVED AS WE HEAD INTO A SIGNIFICANT
PATTERN CHANGE BEGINNING TUESDAY.
MONDAY NIGHT INTO TUESDAY, THE AFOREMENTIONED RIDGE WILL WEAKEN
AND GET PUSHED EASTWARD AS THE FIRST OF TWO UPPER-LEVEL TROUGHS
DROP DOWN FROM THE GULF OF ALASKA. THE FIRST TROUGH LOOKS TO
TRACK TOWARDS THE OR/CA BORDER, BUT WILL BRING INCREASING CLOUD
COVER ALONG WITH A 25-50% CHANCE FOR LIGHT SHOWERS. THIS WILL
SUPPORT COOLER TEMPERATURES ACROSS INTERIOR VALLEYS, WITH THE
DAYTIME HIGHS ON TUESDAY FALLING INTO THE LOW TO MID 70S FOR
INLAND VALLEYS, INTO THE 60S FOR THE COAST AND MID 50S TO MID
60S FOR THE CASCADES. WINDS WILL ALSO BEGIN TO TURN MORE
SOUTHERLY, GENERALLY REMAINING RELATIVELY LIGHT WITH GUSTS BELOW
20 MPH. AN EXCEPTION WOULD BE THE COLUMBIA RIVER GORGE AND HOOD
RIVER VALLEY, WHERE WESTERLY GAP WINDS TUESDAY AFTERNOON WITH
GUSTS APPROACHING 35 MPH WITH A 30-50% CHANCE FOR MAXIMUM GUSTS
EXCEEDING 40 MPH. -42/10
LONG TERM...WEDNESDAY THROUGH SUNDAY
WEDNESDAY INTO THURSDAY
CONTINUES TO BE FAR MORE IMPACTFUL IN TERMS OF PRECIPITATION AS
THE MAJORITY OF ENSEMBLE MEMBERS CONTINUE TO SHOW A SECOND,
MUCH DEEPER UPPER-LEVEL TROUGH DROPPING DOWN OUT OF THE GULF OF
ALASKA AND INTO THE PACIFIC NORTHWEST. THE ASSOCIATED SURFACE
FRONT WITH THIS MORE ROBUST SYSTEM SWINGS THROUGH ON WEDNESDAY,
BRINGING WIDESPREAD RAIN, COOLER TEMPERATURES, AND BREEZIER
WINDS FROM THE SOUTH. IN ADDITION, THERE WILL BE A 10-20% CHANCE
FOR THUNDERSTORMS. CHANCES FOR EXCEEDING 1 INCH OF RAIN IN 48
HOURS BETWEEN 5 AM WEDNESDAY TO 5 AM FRIDAY ARE HIGH (70-90%)
ACROSS NORTHWEST OREGON AND SOUTHWEST WASHINGTON, WITH THE
HIGHEST CHANCES ALONG THE COAST, COAST RANGE, AND CASCADES.
CHANCES FOR EXCEEDING 2 INCHES DURING THIS SAME TIMEFRAME ARE
AROUND 35-50% FOR THESE HIGHER TERRAIN FEATURES, AND 5-15% ALONG
THE I-5 CORRIDOR. IT SHOULD BE NOTED THAT THE PRIMARY CAUSE FOR
THE UNCERTAINTY IS THE EXACT TRACK OF THIS LOW. WHILE MOST
ENSEMBLES SHOW THE CENTER OF THE LOW COMING ON SHORE SOUTH OF
THE OLYMPIC PENINSULA AND THEN MOVING EASTWARD, SOME SOLUTIONS
DO HAVE THIS LOW SLOWING DOWN AND HUGGING THE OR/WA COAST BEFORE
PUSHING INLAND NEAR THE MOUTH OF THE COLUMBIA RIVER BAR. A MORE
SOUTHERLY TRACK COULD RESULT IN PRECIPITATION TOTALS BEING
SLIGHTLY LESS THAN CURRENTLY FORECASTED.
THURSDAY AFTERNOON TO SATURDAY, THE UPPER-LEVEL TROUGH REMAINS
OVER THE PACIFIC NORTHWEST AND WE TRANSITION INTO A POST-FRONTAL
ENVIRONMENT WITH LINGERING SHOWERS OVER THE CWA. GIVEN THAT
THERE WILL BE COOLER AIR ALOFT, THIS WILL FAVOR INCREASING
ATMOSPHERIC INSTABILITY AND THUS CHANCES FOR THUNDERSTORMS.
THERE WILL BE ANOTHER 10-20% CHANCE FOR THUNDERSTORMS ON
THURSDAY FOLLOWING THE INITIAL FRONTAL PASSAGE. ANY PASSING
THUNDERSTORMS MAY PRODUCE LIGHTNING, HEAVY RAIN, ERRATIC WINDS,
AND SMALL HAIL. OVERALL, WHILE THE UPCOMING RAIN WILL NOT
QUITE YET BE A "FIRE SEASON ENDER," IT WILL DEFINITELY SLOW DOWN
FIRE SEASON AND HELP PUT A DAMPER ON ONGOING WILDFIRES. -42/10
AVIATION...THROUGH 18Z TUESDAY
VFR CONDITIONS EXPECTED TO
REMAIN IN PLACE ACROSS THE AIRSPACE INTO THIS EVENING AT COASTAL
TERMINALS, AND INTO TONIGHT INLAND. LARGELY CLEAR SKIES WILL
PERSIST THROUGH TODAY, WITH WINDS RISING TO 5-10 KT INLAND AND
TO 8-12 KT ALONG THE COAST. WEAKENING OFFSHORE FLOW EARLY WILL
SEE EAST WINDS THROUGH THE COLUMBIA GORGE AND NORTH WINDS ALONG
THE WILLAMETTE VALLEY BEGIN TO SHIFT OUT OF THE WEST TO
SOUTHWEST AS ONSHORE FLOW IS RE-ESTABLISHED BY THIS AFTERNOON.
THIS EVENING AND TONIGHT, AN ONSHORE PUSH WILL SEE 70-80%
CHANCES OF IFR CIGS AT COASTAL TERMINALS AFTER 02-04Z TUE, AND
60-80% CHANCES OF MVFR CIGS AT INLAND TERMINALS AFTER 10-12Z
TUE, INCREASING OVERNIGHT FROM SOUTH TO NORTH. WINDS SHIFT OUT
OF THE SOUTH TO SOUTHWEST THIS EVENING AND OVERNIGHT AHEAD OF AN
APPROACHING FRONTAL SYSTEM OVER THE NORTHEAST PACIFIC.
KPDX AND APPROACHES...VFR CONDITIONS EXPECTED INTO TONIGHT.
NORTHWEST WINDS OF 5-10 KT SHIFT SOUTHERLY THIS EVENING AS A
MARINE PUSH BRINGS 70-80% CHANCE OF MVFR CIGS AFTER 12Z TUE. -36
MARINE
WEAK RIDGING OVER THE REGION WILL MAINTAIN
NORTH/NORTHWEST WINDS THROUGH TONIGHT. THERMAL TROUGHING ALONG
THE COAST WILL RESULT IN STRENGTHENING NEAR-SHORE WINDS THIS
AFTERNOON WITH GUSTS TO 25 KT WITHIN 10-20 NM NORTH OF CAPE
FALCON AND INCLUDING THE COLUMBIA RIVER BAR. WILL MAINTAIN THE
CURRENT SMALL CRAFT ADVISORY FROM 2 PM TO 8 PM PDT THIS
AFTERNOON AND EVENING. LARGELY WIND- DRIVEN SEAS WILL PERSIST AT
4-6 FT DURING THIS PERIOD.
ON TUESDAY, WINDS BECOME SOUTHERLY AS THE START OF A WIDESPREAD
PATTERN CHANGE IS EXPECTED. A SERIES OF ROBUST TROUGHS, DIVING OUT
OF THE GULF OF ALASKA AND SUBSEQUENTLY MOVING EASTWARD OVER THE
PAC NW WILL BRING ABOUT INCREASING WINDS AND BUILDING SEAS ACROSS
ALL WATERS. BY TUESDAY EVENING/WEDNESDAY MORNING, A ROBUST
FRONTAL SYSTEM WILL MOVE ACROSS ALL FORECAST ZONES. THIS FRONTAL
SYSTEM WILL RESULT IN SOUTHERLY WIND GUSTS UP TO 40 KT AS WELL AS
SEAS BUILDING TOWARDS 10-12 FT ACROSS ALL WATERS. THEREFORE, HAVE
ISSUED A GALE WATCH FOR ALL WATERS AS WELL AS THE COLUMBIA RIVER
BAR STARTING TUESDAY EVENING THROUGH AT LEAST WEDNESDAY EVENING.
THERE IS AROUND A 20% CHANCE FOR GUSTS UP TO 50 KT THROUGH THE
GALE WATCH TIME FRAME, WITH HIGHEST PROBABILITY WITHIN THE NEAR-
SHORE WATERS. ALSO, THERE IS A LESS THAN 10% CHANCE AT THIS TIME
FOR SIGNIFICANT WAVE HEIGHTS TO REACH 15 FT. BEHIND THIS SYSTEM,
WINDS AND SEAS ARE EXPECTED TO EASE BELOW 15 KT AND 8 FT FOR THE
REMAINDER OF THE WEEK AND INTO THE WEEKEND. -42/36
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 2 PM THIS AFTERNOON TO 8 PM PDT THIS
EVENING FOR PZZ210-251.
GALE WATCH FROM TUESDAY EVENING THROUGH WEDNESDAY EVENING FOR
PZZ210-251>253-271>273.
WWW.WEATHER.GOV/PORTLAND
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