596
FXUS66 KPQR 201102 AAA
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
359 AM PDT MON OCT 20 2025
SYNOPSIS
HIGH PRESSURE WILL BRING DRY AND CALM WEATHER WITH MILD
AFTERNOON TEMPERATURES MONDAY AND TUESDAY. THEN, A SERIES OF WEATHER
SYSTEMS FROM LATE WEDNESDAY ONWARD WILL BRING SEVERAL ROUNDS OF
WIDESPREAD RAIN TO THE AREA THROUGH THE WEEKEND, LIKELY HEAVIEST ON
FRIDAY AS A MODERATE ATMOSPHERIC RIVER PUSHES INLAND. BREEZY SOUTH
WINDS APPEAR LIKELY LATE THURSDAY INTO FRIDAY AND AGAIN FRIDAY NIGHT
INTO SATURDAY, STRONGEST ALONG THE COAST.
SHORT TERM...NOW THROUGH TUESDAY NIGHT
THE SHORT TERM FORECAST IS
HIGHLIGHTED BY MAINLY DRY AND CALM CONDITIONS WITH MILD AFTERNOON
TEMPERATURES. WHILE RADAR AND SURFACE WEATHER OBSERVATIONS FROM 2-4
AM PDT MONDAY SHOWED ISOLATED LIGHT RAIN SHOWERS LINGERING OVER
SOUTHWEST WA AND THE NORTH OR COAST RANGE, THESE SHOWERS SHOULD
DIMINISH BY LATE MORNING AS SURFACE HIGH PRESSURE CONTINUES TO
STRENGTHEN OVER THE AREA. OTHERWISE EXPECT DRY CONDITIONS TODAY WITH
A MIX OF SUN AND CLOUDS THIS MORNING, ALONG WITH PATCHY MORNING FOG
IN THE SOUTHERN WILLAMETTE VALLEY AND LANE/LINN COUNTY CASCADE
FOOTHILLS. SKIES SHOULD BECOME MOSTLY SUNNY THIS AFTERNOON FOR ALL OF
NORTHWEST OR AND SOUTHWEST WA, ALLOWING TEMPERATURES TO WARM INTO THE
LOW TO MID 60S.
CLEAR SKIES AND CALM WINDS MONDAY EVENING WILL SET THE STAGE FOR
RAPIDLY COOLING TEMPERATURES OVERNIGHT FOR INLAND VALLEYS. IT APPEARS
SOME LOW CLOUDS AND PATCHY FOG WILL ATTEMPT TO DEVELOP OVER PORTIONS
OF THE WILLAMETTE VALLEY LATE MONDAY NIGHT, HELPING TO LIMIT THE
POTENTIAL FOR FROST DEVELOPMENT. NEVERTHELESS, ANY CLOUD DEVELOPMENT
SHOULD HOLD OFF LONG ENOUGH TO ALLOW TEMPERATURES TO DIP INTO THE
UPPER 30S FOR OUTLYING RURAL AREAS, AND TO AROUND 40 DEGREES IN URBAN
AREAS. THE UPPER HOOD RIVER VALLEY WILL LIKELY DIP INTO THE MID 30S
WITH FROST POSSIBLE, HOWEVER THIS ZONE HAS ALREADY OBSERVED
SUB-FREEZING TEMPERATURES MULTIPLE TIMES THIS MONTH AND IS NO LONGER
ELIGIBLE FOR FROST/FREEZE HEADLINES THIS GROWING SEASON.
EXPECT MOSTLY SUNNY SKIES ON TUESDAY ASIDE FROM SOME LOW CLOUDS OVER
PORTIONS OF THE WILLAMETTE VALLEY IN THE MORNING. LIGHT OFFSHORE FLOW
ALSO DEVELOPS TUESDAY, HELPING BOOST TEMPERATURES A BIT MORE. THE NBM
CONTINUES TO SUGGEST HIGH TEMPERATURES IN THE MID TO UPPER 60S
TUESDAY AFTERNOON, EXCEPT LOWER 70S IN THE CASCADE VALLEYS OF LANE
AND LINN COUNTIES. OVERALL, EXPECT IDEAL FALL WEATHER FOR OUTDOOR
ACTIVITIES. -23
LONG TERM...WEDNESDAY THROUGH SUNDAY NIGHT
IN THE LONG TERM
FORECAST, THE WEATHER PATTERN STILL LOOKS VERY ACTIVE AS A
SERIES OF WEATHER SYSTEMS ASSOCIATED WITH A PARENT LOW PRESSURE
SYSTEM CENTERED NEAR THE GULF OF ALASKA BRING MULTIPLE ROUNDS OF
WIDESPREAD RAIN AND BREEZY SOUTH WINDS TO THE AREA. MODELS ARE IN
FAIRLY GOOD AGREEMENT ON WEDNESDAY, SUGGESTING A WEAKER FRONTAL
SYSTEM WILL PUSH INLAND LATE IN THE DAY AND BRING LIGHT RAIN INTO THE
AREA. THEN, A POTENTIALLY STRONGER SYSTEM ARRIVES THURSDAY NIGHT INTO
FRIDAY AS AN ATMOSPHERIC RIVER WITH FORECASTED IVT VALUES PEAKING
AROUND 600-800 KG/M/S PUSHES INLAND. THIS SYSTEM WILL BRING HEAVIER
STRATIFORM RAIN FROM THE COAST TO THE CASCADES, QUICKLY FOLLOWED BY
ANOTHER SYSTEM BRINGING CONTINUED RAIN AND BREEZY SOUTH WINDS
SATURDAY INTO SUNDAY.
WITH RELATIVELY LOW RIVER LEVELS LEADING INTO THIS EVENT, RIVER
FLOODING IS NOT EXPECTED. THAT SAID, CANNOT COMPLETELY RULE OUT MINOR
URBAN FLOODING AND SMALL STREAM FLOODING DEPENDING ON FRONTAL FORCING
AND HOURLY RAIN RATES. DETAILS ON THESE FACTORS ARE CURRENTLY UNCLEAR
GIVEN THE LEAD TIME INVOLVED. NEVERTHELESS, WPC'S TOTAL QPF AMOUNTS
FROM 5 PM THURSDAY THROUGH 5 AM SUNDAY SUGGEST 1.5-2.5 INCHES OF RAIN
OVER INLAND VALLEYS, AND 3-5 INCHES OF RAIN FOR THE COAST, COASTAL
MOUNTAINS AND CASCADES. THIS IS IN LINE WITH THE LATEST MODEL
ENSEMBLE GUIDANCE AND NBM PROBABILISTIC GUIDANCE. NOTE THE DIFFERENCE
BETWEEN THE NBM 75TH AND 25TH PERCENTILES FOR QPF AMOUNTS IS ONLY
AROUND 1 INCH, SUGGESTING CONFIDENCE IS MODERATE FOR FORECAST RAIN
AMOUNTS. CANNOT SAY CONFIDENCE IS HIGH JUST YET, AS THERE ARE STILL
SOME MODEL ENSEMBLE MEMBERS SHOWING HIGHER RAIN AMOUNTS. THIS IS
REFLECTED WELL BY THE NBM 90TH PERCENTILE FOR 72-HR RAIN AMOUNTS,
WHICH SHOWS 3-3.5 INCHES OVER INLAND VALLEYS AND 4-6.5 INCHES OVER
THE MOUNTAINS. WHILE THE PROBABILITY FOR RAIN AMOUNTS THIS HIGH IS
ONLY AT 10%, IT IS WORTH MENTIONING AS THIS WOULD BE ENOUGH TO
INCREASE HYDRO CONCERNS.
CONFIDENCE IS INCREASING THAT BREEZY SOUTH WINDS WILL ACCOMPANY
THESE SYSTEMS, THOUGH THE PROBABILITY FOR IMPACTFUL WIND GUSTS OF
45-55 MPH OR STRONGER REMAINS FAIRLY LOW FOR INLAND AREAS.
PROBABILITIES ARE RELATIVELY HIGHER AT THE COAST. WINDS ALONG THE
COAST NOW LOOK TO BE STRONGEST LATE THURSDAY INTO FRIDAY WITH THE
FIRST SYSTEM. BETWEEN 11 PM THURSDAY AND 11 PM FRIDAY, THE NBM
CONTINUES TO INDICATE A 45-65% CHANCE OF WIND GUSTS OVER 45 MPH, A
20-35% CHANCE OF WIND GUSTS OVER 50 MPH, AND 5-20% CHANCE OF WIND
GUSTS OVER 55 MPH. INLAND, PROBABILITIES FOR WIND GUSTS OVER 45 MPH
REMAIN UNDER 10% WITH THIS FIRST SYSTEM. HOWEVER, INLAND WIND GUSTS
NOW LOOK TO PEAK ON SATURDAY WITH THE SECOND SYSTEM, THOUGH BREEZY
WINDS ARE STILL LIKELY ALONG THE COAST, AS WELL. BETWEEN 11 PM
FRIDAY AND 11 PM SATURDAY, THE NBM INDICATES A 20-40% CHANCE OF WIND
GUSTS OVER 40 MPH AND A 15-25% CHANCE OF WIND GUSTS OVER 45 MPH FOR
INLAND AREAS, A SLIGHT UPTICK FROM LAST NIGHT'S NBM GUIDANCE. ALONG
THE COAST, THE NBM INDICATES A 30-50% CHANCE OF WIND GUSTS OVER 45
MPH, A 20-30% CHANCE OF WIND GUSTS OVER 50 MPH, AND A 15-25%
CHANCE OF WIND GUSTS OVER 55 MPH. WHILE WIND GUSTS OF THESE STRONGER
MAGNITUDES ARE UNLIKELY TO OCCUR, THE POTENTIAL IS WORTH MENTIONING
AS THESE WINDS WOULD BE STRONG ENOUGH TO RESULT IN WIDESPREAD DOWNED
TREES AND POWER OUTAGES. THIS WOULD BE ESPECIALLY TRUE AS FOLIAGE IS
STILL ON MANY TREES AND SOIL CONDITIONS WILL BE WET.
ALSO WORTH MENTIONING IS LOWERING SNOW LEVELS SATURDAY INTO
SATURDAY NIGHT AND SUNDAY AS COLDER AIR ALOFT SETTLES OVER THE AREA.
THE DETERMINISTIC NBM SUGGESTS SNOW LEVELS WILL FALL TO 3500-4500
FEET BY SATURDAY NIGHT, WHILE THE 10TH PERCENTILE SUGGESTS SNOW
LEVELS DOWN TO 3000-3500 FEET (10% CHANCE OF OCCURRING). IN BOTH
CASES, ACCUMULATING SNOW WOULD OCCUR AT PASS LEVEL, RESULTING IN
TRAVEL IMPACTS. -23/03
AVIATION
SHOWERS HAVE GENERALLY DISSIPATED OVER THE AREA EARLY
MONDAY MORNING AS HIGH PRESSURE STRENGTHENS. THE MAIN EXCEPTION IF
NEAR KAST AND IN THE SOUTH WA/NORTH OR CASCADES, WHERE ISOLATED
LIGHT SHOWERS WILL REMAIN IN PLACE THROUGH APPROXIMATELY 18Z
MONDAY. EXPECT MAINLY VFR FLIGHT CONDITIONS TODAY AND TONIGHT,
ASIDE FROM 09-17Z MONDAY WHEN PATCHY FOG IS POSSIBLE. KEUG AND
KHIO HAVE THE BEST CHANCE TO SEE VISIBILITY REDUCTIONS DUE TO FOG,
AS LOW AS 1/2 SM TO 1 SM AT TIMES. FOG HAS ALREADY DEVELOPED AT
KEUG AS OF 09Z.
KPDX AND APPROACHES...PREDOMINATELY VFR EXPECTED THROUGH THE
PERIOD. A FEW LIGHT RAIN SHOWERS IN THE VICINITY OF THE AIRPORT
SHOULD DIMINISH BY 12-14Z MONDAY. -23
MARINE
BUOY OBSERVATIONS FROM EARLY MONDAY MORNING SHOW SEAS
HAVE FALLEN TO 15 TO 17 FT WITH A DOMINANT WAVE PERIOD BETWEEN 11
AND 14 SECONDS. WINDS WERE OUT OF THE WEST TO NORTHWEST AROUND 5
TO 15 KT. SEAS ARE EXPECTED TO CONTINUE GRADUALLY SUBSIDING TO
AROUND 10 TO 12 FT AT 13 SECONDS BY MID MONDAY AFTERNOON. THE
HAZARDOUS SEAS WARNING REMAINS IN EFFECT UNTIL 8 AM MONDAY, WITH
SMALL CRAFT ADVISORIES IN EFFECT AFTERWARDS THROUGH MONDAY
AFTERNOON. LIGHT WINDS AND LOWER SEAS HOLD THROUGH MONDAY NIGHT.
ANOTHER POTENT NORTHWESTERLY SWELL THEN ARRIVES TUESDAY AFTERNOON,
PUSHING SEAS UP TO THE 15 TO 18 FT RANGE. AFTER A BRIEF BREAK
WEDNESDAY, AN ACTIVE WEATHER PATTERN IS THEN EXPECTED TO CONTINUE
THURSDAY THROUGH SATURDAY NIGHT WITH A PERIOD OF STORM FORCE
SOUTHERLY WIND GUSTS OF 48 KT OR STRONGER POSSIBLE THURSDAY NIGHT
INTO FRIDAY MORNING (20-30% CHANCE OVER THE OUTER WATERS AND A
30-50% CHANCE OVER THE INNER WATERS). NOTE THAT PROBABILITIES ARE
HIGHEST OVER THE INNER WATERS DUE TO THE POTENTIAL DEVELOPMENT OF
A COASTAL JET DURING THAT TIME. THIS SYSTEM WILL LIKELY PUSH SEAS
UP TO AROUND 20 FT AGAIN, WITH A 10% CHANCE FOR SEAS OVER 20 FT. -23
BEACH HAZARDS
RAZOR CLAM DIGGERS AT THE COAST WILL NEED TO
EXERCISE CAUTION FOR SNEAKER WAVES THIS WEEK, ESPECIALLY ON
TUESDAY AND WEDNESDAY WHEN A LONG PERIOD WESTERLY SWELL WILL BRING
A HIGH THREAT FOR SNEAKER WAVES. SNEAKER WAVES CAN RUN UP
SIGNIFICANTLY FARTHER ON A BEACH THAN NORMAL, INCLUDING OVER
ROCKS, LOGS, AND JETTIES. SNEAKER WAVES CAN SUDDENLY KNOCK PEOPLE
OFF OF THEIR FEET AND QUICKLY PULL THEM INTO THE OCEAN WHICH MAY
LEAD TO SERIOUS INJURY OR DROWNING. CAUTION SHOULD BE USED WHEN IN
OR NEAR THE WATER. ALWAYS KEEP AN EYE ON THE WAVES, AND BE
ESPECIALLY WATCHFUL OF CHILDREN AND PETS. REMEMBER, NEVER TURN
YOUR BACK ON THE OCEAN. A BEACH HAZARDS STATEMENT IS IN EFFECT
ACROSS THE CENTRAL AND NORTHERN OREGON COAST AND THE SOUTH
WASHINGTON COAST TUESDAY MORNING THROUGH WEDNESDAY AFTERNOON TO
HELP MESSAGE THIS THREAT. -23
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...HAZARDOUS SEAS WARNING UNTIL 8 AM PDT THIS MORNING FOR PZZ210-
251>253-271>273.
SMALL CRAFT ADVISORY FROM 8 AM THIS MORNING TO 8 PM PDT THIS
EVENING FOR PZZ210-251>253-271>273.
WWW.WEATHER.GOV/PORTLAND
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