537
FXUS66 KPQR 202214
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
314 PM PDT MON OCT 20 2025
SYNOPSIS
HIGH PRESSURE WILL BRING DRY AND CALM WEATHER WITH
MILD AFTERNOON TEMPERATURES THROUGH TUESDAY. STARTING ON
WEDNESDAY, A SERIES OF FRONTAL SYSTEMS STEMMING FROM A BROAD LOW
IN THE GULF OF ALASKA WILL MOVE OVER THE REGION. WE ARE LOOKING
AT A PROLONGED PERIOD OF RAIN, WIND AND CASCADE SNOW. A TREND
TOWARDS A MODERATE ATMOSPHERIC RIVER (AR) ON FRIDAY WILL BE
ACCOMPANIED BY GUSTY SOUTH TO SOUTHWESTERLY WINDS. SNOW LEVELS
WILL BEGIN TO DROP OVER THE WEEKEND WITH SNOW POSSIBLE ALONG THE
PASSES.
SHORT TERM...NOW THROUGH TUESDAY NIGHT
A WEAKENING AREA OF
HIGH PRESSURE PERSISTS OVER THE REGION THROUGH TUESDAY AND
BEGINS TO ERODE ON WEDNESDAY. THIS HIGH WILL MAINTAIN PARTIALLY
CLOUDY SKIES, DRIER CONDITIONS ASIDE FROM A FEW SHOWERS ALONG
THE NORTH OREGON AND SOUTH WASHINGTON COASTS. TEMPERATURES WILL
REMAIN SEASONABLE WITH HIGHS IN THE 60S AND LOWS IN THE 40S.
IN THE SHORT-TERM, FOG IS GOING TO BE A WEATHER FEATURE TO WATCH
OUT FOR. AS IS TYPICAL FOR THIS TIME OF YEAR, CLEARING SKIES
WITH LINGERING MOISTURE WILL AID IN DECREASING THE DEWPOINT
DEPRESSION AND THUS INCREASE CHANCES FOR FOG. WHILE MODELS DO
NOT NECESSARILY DEPICT THE PRESENCE WELL, THE LIGHT NORTHERLY
WINDS COMBINED WITH THESE TWO OTHER COMPONENTS WILL SET UP THE
ATMOSPHERE FOR FOG DEVELOPMENT. THIS WILL MAINLY BE THE CASE IN
OUR MORE "FOG PRONE" AREAS LIKE EUGENE, ALONG THE I-5 CORRIDOR
AND HILLSBORO.
SIMILAR CONDITIONS EXPECTED THROUGH TUESDAY AND THEN BEGIN TO
DETERIORATE ON WEDNESDAY AFTERNOON AS THE FIRST FRONTAL SYSTEM
APPROACHES. -27
LONG TERM...WEDNESDAY THROUGH SUNDAY NIGHT
FALL IS IN FULL
SWING AS THE FIRST OF MULTIPLE FRONTAL SYSTEMS APPROACH THE
REGION. THESE SYSTEMS ARE STEMMING FROM A LARGE "PARENT" LOW IN
THE GULF OF ALASKA. THIS LOW IS COLD WRAPPED AND PRODUCING
SEVERAL SHORT AND LONG WAVE TROUGHS. THE FIRST TROUGH IS FAIRLY
ORGANIZED AS OBSERVED IN THE ENSEMBLE LOW CENTERS. THIS SYSTEM
WILL MOVE OVER NORTHWEST OREGON AND SOUTHWEST WASHINGTON EARLY
WEDNESDAY MORNING BUT WILL BE SHOWERY AS WE SIT ON THE SOUTHERN
EDGE OF THE RAIN BAND. AT THIS POINT, THE ATMOSPHERE IS STILL
FAIRLY WARM SO THERE IS A LOW PROBABILITY OF THUNDERSTORMS, BUT
ACCUMULATING PRECIPITATION CHANCES ARE INCREASING. ANY RAIN
THAT DOES ACCUMULATE WILL BE MINIMAL WITH A 35% CHANCE OF 0.1
INCH OF RAIN IN THE NORTHERN WILLAMETTE VALLEY, AROUND 65% ALONG
THE COAST NEAR ASTORIA AND LOWERING PROBABILITIES AS YOU MOVE
SOUTHWARD. AS THIS SYSTEM QUICKLY EXITS, ZONAL FLOW WITH
ADVANCING COOLER AIR DEVELOPS. THURSDAY WILL SEE MINIMAL IF ANY
RAIN AND MOSTLY CLOUDY SKIES.
FRIDAY IS WHEN THINGS REALLY BEGIN TO GET SPICY IN THE WEATHER
WORLD. AN MODERATE ATMOSPHERIC RIVER (AR) WILL BEGIN TO PUSH
INLAND FROM THE SOUTHWEST. THIS AR WILL BRING AMPLE
PRECIPITATION, STRONG SOUTH TO SOUTHWESTERLY WINDS, AND A BURST
OF WARMER AIR BEFORE TRAILING COOLER AIR MOVES IN. AS OF RIGHT
NOW THERE IS STILL A WIDE RANGE OF PROBABILITIES FOR BOTH WIND
AND RAIN. IMPACT WISE, RAIN HAS A LOWER PROBABILITY OF ISSUES AS
ACCUMULATION RATES ARE NOT HIGH ENOUGH TO PRODUCE SIGNIFICANT
URBAN FLOODING AT THIS TIME. GLOBAL ENSEMBLES ARE SHOWING AROUND
1 INCH IN 3 HOURS WHICH IS A LITTLE MORE THAN A QUARTER INCH PER
HOUR. WITH THESE RAIN RATES, CLEARED DRAINS SHOULDN'T HAVE ANY
ISSUES RIDDING WATER. HOWEVER, GIVEN THE TIME OF YEAR AND FALLEN
LEAVES, THOSE CLOGGED DRAINS COULD PRODUCE A PROBLEM CAUSING
LOCALIZED PONDING THAT COULD CAUSE IMPACTS TO TRAFFIC.
WIND WILL BE ANOTHER CONCERN BUT ONE THAT HAS SIGNIFICANTLY MORE
VARIABILITY. THE COAST WILL SEE THE HIGHEST WIND SPEEDS,
ESPECIALLY ALONG THE BEACHES AND HEADLANDS. ALONG COASTAL
CITIES, WINDS COULD BE AS LOW AS 30 MPH, OR AS HIGH AS 60 MPH
(THE 10TH TO 90TH PERCENTILE). INLAND, GUSTS COULD RANGE, BASED
ON THE 10TH TO 90TH, BETWEEN 20 MPH TO NEARLY 50 MPH ON FRIDAY
AFTERNOON INTO SATURDAY MORNING. THIS SPREAD MAKES NARROWING
DOWN ON AN EXACT FORECAST DIFFICULT. FOR RAINFALL TOTALS TOO
WILL BE HIGHER AS THE STRONGER BAND OF PRECIPITATION RUNS OVER
ON FRIDAY. ULTIMATELY THE RAIN COMBINED WITH WIND AND FULL
LEAFED TREES COULD LEAD TO DOWNED BRANCHES AND SOME HEAVIER
TREES.
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.
RAIN WILL CONTINUE INTO EARLY NEXT WEEK. -27
AVIATION
PATCHES OF FOG AND LOW CLOUDS REMAIN IN PLACE ACROSS
PORTIONS OF THE WILLAMETTE VALLEY. EXPECT THE FOG AND LOW CLOUDS
TO GRADUALLY LIFT AND SCATTER OUT OVER THE NEXT 1-3 HOURS.
THIS WILL RESULT IN VFR CONDITIONS AWAY FROM THE TERRAIN FOR THE
REMAINDER OF THIS AFTERNOON AND EVENING. LIGHT WINDS AND CLEAR
SKIES OVERNIGHT WILL LEAD TO AREAS OF FOG AND LOW CLOUDS
REDEVELOPING. OUR LATEST STATISTICAL GUIDANCE SUGGESTS A 25-40%
CHANCE OF MVFR OR LOWER CONDITIONS DEVELOPING AT ANY GIVEN HOUR
BETWEEN 09-18Z TUESDAY WITH THE HIGHEST PROBABILITIES AT KHIO
AND KEUG AND LOWER PROBABILITIES AT SITES LIKE KPDX AND KSLE.
KPDX AND APPROACHES...BUILDING HIGH PRESSURE WILL LEAD TO
PREDOMINANTLY VFR CONDITIONS THROUGH 18Z TUESDAY. THE MAIN
EXCEPTION TO THIS WILL BE LATE TONIGHT AND TUESDAY MORNING WHEN
LIGHT WINDS AND CLEAR SKIES WILL LEAD TO AREAS OF FOG AND LOW
CLOUDS DEVELOPING. OUR LATEST STATISTICAL GUIDANCE SUGGESTS
JUST A 25% CHANCE OF MVFR OR LOWER CONDITIONS DEVELOPING AT ANY
GIVEN HOUR BETWEEN 12-18Z TUESDAY AT KPDX, BUT SUSPECT THE
PROBABILITY OF SUCH FLIGHT DETERIORATIONS IS HIGHER THAN THIS SO
HAVE PUT MIST AND FOG INTO THE TAF FOR TUESDAY MORNING.
MARINE
SEAS ARE EXPECTED TO CONTINUE GRADUALLY SUBSIDING TO
AROUND 10 TO 12 FT AT 13 SECONDS BY MID 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...SMALL CRAFT ADVISORY UNTIL 8 PM PDT THIS EVENING FOR PZZ210-
251>253-271>273.
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