521
FXUS66 KPQR 081826
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
1126 AM PDT TUE SEP 8 2026
SYNOPSIS
DRIER AND WARMER CONDITIONS PERSIST THROUGH
THURSDAY WITH TEMPERATURES GRADUALLY WARMING AND PEAKING
TOMORROW WITH THE DEVELOPMENT OF LOW-LEVEL OFFSHORE FLOW. COOLER
TEMPERATURES RETURN ON FRIDAY AND WILL CONTINUE THROUGH THE
WEEKEND, ALONG WITH INCREASING CHANCES FOR RAIN. THE FORECAST
BECOMES MORE UNCERTAIN BY THE START OF NEXT WEEK, WITH THE
POTENTIAL FOR WEATHER CONDITIONS TO RANGE ANYWHERE FROM COOL AND
SHOWERY TO WARM AND DRY DEPENDING ON THE EVOLUTION OF THE LARGE
SCALE WEATHER PATTERN.
DISCUSSION...TUESDAY AFTERNOON THROUGH MONDAY
SATELLITE
IMAGERY EARLY THIS AFTERNOON SHOWS MOSTLY CLEAR SKIES ACROSS NW
OR AND SW WA. ENSEMBLE GUIDANCE REMAINS IN GOOD AGREEMENT THAT
UPPER HEIGHTS OVER THE PACNW WILL RAISE INTO WEDNESDAY AS THE
UPPER LOW FROM PREVIOUS DAYS CONTINUES MOVING EASTWARD INTO THE
NORTHERN PLAINS AND HIGH PRESSURE OVER THE DESERT SW SLOWLY
SPREADS INTO THE WESTERN US. IN ADDITION TO THESE TWO SYNOPTIC
FEATURES OVER CONUS, A TROPICAL/SUB-TROPICAL LOW OFF THE COAST
OF CALIFORNIA ALONG WITH AN UPPER LEVEL HIGH OVER THE NE
PACIFIC WILL CREATE A COL OVER THE PAC NW. THIS COL WILL HELP TO
MAINTAIN RATHER BENIGN CONDITIONS THROUGH THE MIDDLE OF THE
WEEK. AT THE SURFACE, A THERMAL TROUGH WILL PUSH NORTH FROM CA,
BRINGING WEAK OFFSHORE FLOW (EAST WINDS OVER TERRAIN AND THE
COAST AND NORTH WINDS FOR THE INTERIOR LOWLANDS). THIS OVERALL
SETUP WILL BRING CONTINUED DRY WEATHER AS WELL AS A BRIEF
WARMING TREND INTO WEDNESDAY. DAYTIME TEMPERATURES ARE EXPECTED
TO RISE INTO THE UPPER 70S TO AROUND 80 DEGREES FOR THE INTERIOR
LOWLANDS TODAY AND LOW TO MID 80S ON WEDNESDAY. COASTAL
COMMUNITIES WILL ALSO BE WARMER DUE TO THE OFFSHORE FLOW, IN THE
UPPER 60S TO LOW 70S TODAY AND LOW TO MID 70S ON WEDNESDAY.
THERE'S AROUND A 5-10% CHANCE THAT COASTAL CITIES OFF THE
IMMEDIATE COAST COULD REACH 80 DEGREES ON WEDNESDAY IF OFFSHORE
FLOW CONTINUES INTO WEDNESDAY AFTERNOON/EARLY EVENING.
ENSEMBLE MEMBERS REMAIN IN GOOD TO EXCELLENT AGREEMENT ON THE
WEATHER PATTERN FOR THURSDAY INTO SATURDAY. ON THURSDAY, A WEAK
TROUGH BEGINS PUSHING SOUTH INTO THE PACNW, LOWERING HEIGHTS
AND PUSHING THE SURFACE THERMAL TROUGH SOUTH. THIS WILL ALLOW
TEMPERATURES TO LOWER BACK TO NEAR TO SLIGHTLY BELOW NORMAL FOR
EARLY SEPTEMBER (UPPER 70S FOR THE INTERIOR LOWLANDS), THOUGH
DRY CONDITIONS WILL CONTINUE.
ON FRIDAY, ENSEMBLE MEMBERS INDICATE ANOTHER, MORE ROBUST LOW
WILL DEVELOP OVER FAR WESTERN CANADIAN AND DROP SOUTH INTO THE
PACNW FOR THE END OF THE WEEK AND THE START OF THE WEEKEND.
UNCERTAINTY STILL EXISTS ON THE EXACT TRACK, STRENGTH AND
TIMING OF THIS LOW WITH 80% OF MEMBERS SUGGESTING THE TROUGH
WILL DEEPEN ALONG THE COAST WHILE THE OTHER 20% SUGGEST THE
TROUGH WILL DEEPEN A LITTLE MORE INLAND OVER EASTERN WA AND
EASTERN OR. AS SUNDAY APPROACHES, THE MAJORITY OF ENSEMBLE
MODELS, AROUND 60-70%, INDICATE THE TROUGH WILL MOVE EAST OF
THE CASCADES BY SUNDAY MORNING WHERE THE OTHER 30-40% SUGGEST
THE TROUGH WILL LINGER LONGER INTO THE DAY ON SUNDAY WITH AROUND
10-15% KEEPING THE TROUGH OVER THE PACNW INTO MONDAY.
EVEN WITH THE UNCERTAINTY, NEARLY ALL MEMBERS INDICATE RAIN
WILL RETURN TO THE AREA SOMETIME BETWEEN FRIDAY NIGHT AND
SUNDAY, THOUGH THE EXACT TRACK WILL DETERMINE HOW MUCH RAIN AND
WHERE IT WILL FALL. FRIDAY NIGHT INTO SATURDAY HAS THE HIGHEST
CONFIDENCE WITH THE LATEST NBM DETERMINISTIC FORECAST NOW
INDICATING A 40-50% CHANCE OF RAIN LATE FRIDAY INTO SATURDAY
NIGHT ACROSS THE ENTIRE FORECAST AREA. PART OF THE REASON FOR
THE LOWER PROBABILITIES IS LIKELY MORE TO DO WITH THE TIMING OF
WHEN THE TROUGH WILL PUSH THROUGH THE AREA AS OPPOSED TO WHETHER
IT WILL ACTUALLY RAIN OR NOT. THERE'S A 70-80% CHANCE THAT ANY
LOCATION, WITHIN OUR CWA, WILL RECEIVE AT LEAST 0.01 INCH OF
RAIN IN THE 48 HOURS ENDING AT 5 AM MONDAY. WHEN LOOKING AT
PROBABILITIES OF REACHING OR EXCEEDING 0.25 INCH IN THE SAME 48
HOUR PERIOD, THERE'S A 30-50% CHANCE FOR LOCATIONS WEST OF THE
CASCADES WITH A 45-65% CHANCE OVER THE CASCADES, INCLUDING THE
FOOTHILLS. TEMPERATURES WILL ALSO FALL FAIRLY DRAMATICALLY.
DAYTIME TEMPERATURES WILL BE ANYWHERE FROM 6-10 DEGREES COOLER
ON FRIDAY THAN THURSDAY WITH ANOTHER 2-6 DEGREES OF COOLING ON
SATURDAY. HOWEVER, THE FORECAST TEMPERATURE SPREAD INCREASES
SATURDAY INTO SUNDAY AS THE UNCERTAINTY IN THE WEATHER PATTERN
INCREASES. THE 10TH TO 90TH PERCENTILE SPREAD FOR THE INTERIOR
LOWLANDS ON SATURDAY IS FROM THE LOW 60S TO MID 70S INCREASING
TO THE MID 60S TO LOW 80S ON SUNDAY. IF YOU HAVE OUTDOOR PLANS
THIS WEEKEND, KEEP AN EYE ON THE FORECAST AND PLAN ACCORDINGLY
FOR THE RAIN POTENTIAL. EVEN WITH THE 10-15% OF ENSEMBLE
MEMBERS KEEPING THE UPPER TROUGH OVER THE REGION ON MONDAY,
MEMBERS INDICATE IT WOULD WEAKEN AND LIMIT PRECIPITATION
CHANCES. THE REST OF THE MEMBERS INDICATE DRY AND WARMER
CONDITIONS FOR MONDAY, WHICH IS REFLECTED IN THE DETERMINISTIC
NBM WITH PRECIPITATION CHANCES LESS THAN 10% WITH TEMPERATURES
IN THE 70S FOR THE INTERIOR LOWLANDS. /42-03
AVIATION...THROUGH 18Z WEDNESDAY
HIGH PRESSURE WILL GRADUALLY
BUILD OVER THE REGION TODAY THROUGH WEDNESDAY. PREDOMINATELY VFR
CONDITIONS ARE EXPECTED THROUGH THIS EVENING UNDER MOSTLY CLEAR
SKIES. THERE IS AROUND A 20-30% CHANCE FOR LOW STRATUS AND/OR FOG
TO DEVELOP AT COASTAL TERMINALS AFTER 12Z WEDNESDAY. NORTHWEST
WINDS ARE EXPECTED TO INCREASE AT THE COAST THIS AFTERNOON WITH
GUSTS UP TO 20-25 KT. INLAND, NORTHERLY WINDS INCREASE TO AROUND
8-12 KT WITH GUSTS UP TO 20 KT IN THE SOUTHERLY WILLAMETTE VALLEY.
KPDX AND APPROACHES...VFR CONDITIONS EXPECTED THROUGH THE TAF
PERIOD. LIGHT WINDS BECOME NORTHWEST AROUND 7-9 KT AFTER 20Z THIS
AFTERNOON. /DH
MARINE
HIGH PRESSURE OFFSHORE WILL MAINTAIN PREDOMINATELY
NORTHERLY WINDS ACROSS THE COASTAL WATERS THROUGH THE WEEK. A
STRENGTHENING PRESSURE GRADIENT TODAY WILL BRING STRONGER
NORTHERLIES WITH GUSTS UP TO 25 KT AS THERE IS AN 80% CHANCE OF
WIND GUSTS EXCEEDING 21 KT BY THIS EVENING. AS A RESULT, SMALL
CRAFT ADVISORIES REMAIN IN EFFECT FROM 11 AM TUESDAY TO 6 AM
WEDNESDAY FOR THE OUTER COASTAL WATERS SOUTH OF CAPE FALCON, AND
FROM 2 PM TO 12 PM TUESDAY FOR ALL OTHER COASTAL WATERS. BREEZY
NORTH WINDS CONTINUE THROUGH THURSDAY, BUT SHOULD REMAIN 20 KT OR
LESS. SEAS OF AROUND 4 TO 5 FT WITH A DOMINANT NORTHWEST SWELL AT
10-11 SECONDS WILL GRADUALLY BUILD TO AROUND 6 FT BY THIS EVENING
AS WIND CHOP INCREASES WITH THE NORTHERLY WINDS. A WEAK LOW
PRESSURE SYSTEM IS EXPECTED TO APPROACH THE COASTAL WATERS FROM
THE NORTH LATE FRIDAY INTO SATURDAY. /DH
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 2 PM THIS AFTERNOON TO MIDNIGHT PDT
TONIGHT FOR PZZ210-251>253-271.
SMALL CRAFT ADVISORY UNTIL 6 AM PDT WEDNESDAY FOR
PZZ272-273.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSPORTLAND
X.COM/NWSPORTLAND
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