509
FXUS66 KSEW 210313
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
813 PM PDT MON OCT 20 2025
SYNOPSIS
A WEAK UPPER RIDGE WILL PRODUCE DRIER CONDITIONS FOR
MUCH OF WESTERN WASHINGTON INTO TUESDAY. A FRONTAL SYSTEM WILL
REACH THE AREA ON WEDNESDAY WITH LIGHT PRECIPITATION ACROSS THE
AREA. A DEEP UPPER TROUGH OVER THE GULF OF ALASKA WILL BRING A
A STRONGER FRONTAL SYSTEM INTO THE REGION AT THE END OF THE
WEEK WITH THE POTENTIAL FOR SOME HEAVY RAINFALL. A TROUGH WILL
SETTLE OVER THE AREA BY THE WEEKEND FOR COOLER TEMPERATURES
ALONG WITH PERIODS OF RAIN SHOWERS AND MOUNTAIN SNOW.
SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/
THE LATEST FORECAST REMAINS ON TRACK THIS EVENING WITH NO
FORECAST UPDATES. MID TO HIGH LEVEL CLOUDS WILL CONTINUE TO
SPREAD ACROSS THE AREA AS A WEAK FRONT BRUSHES THE AREA TONIGHT
AND INTO TUESDAY. MOSTLY DRY CONDITIONS WILL CONTINUE THROUGH
TUESDAY, WITH PERIODS OF SUN LIKELY AFTER MORNING FOG AND
STRATUS DISSIPATES. HIGH TEMPERATURES ON TUESDAY WILL BE A TOUCH
WARMER, WITH MOST LOCATIONS IN THE LOWER 60S. AN ADDITIONAL
WEAK FRONT WILL REACH THE AREA ON WEDNESDAY AND WILL BRING SOME
LIGHT RAIN SHOWERS ACROSS THE AREA. THE ATTENTION TURNS INTO A
STRONGER, MORE WETTER FRONTAL SYSTEM APPROACHING THE AREA ON
THURSDAY.
LONG TERM /THURSDAY THROUGH MONDAY/
MOST OF THE CLUSTERS AND ENSEMBLE GUIDANCE ARE IN AGREEMENT
WITH A DEEP UPPER LEVEL TROUGH DIGGING SOUTH OVER THE GULF OF
ALASKA STARTING ON THURSDAY. THIS WOULD ALLOW A FRONTAL SYSTEM
THAT HAS TAPPED INTO SOME SUBTROPICAL MOISTURE TO MOVE OVER
WESTERN WASHINGTON. MODELS HAVE BEEN STILL INCONSISTENT ON HOW
FAST THIS FEATURE IS MOVING, WITH THE LATEST COUPLE OF RUNS
SHIFTING THE MOISTURE MORE SOUTHWARD - WHICH COULD SUGGEST THAT
THIS WOULD BE A MORE SHORT DURATION EVENT OVER OUR AREA.
NONETHELESS, IT DEFINITELY LOOKS LIKE WIDESPREAD MODERATE TO
HEAVY RAIN CAN BE POSSIBLE AT TIMES ALONG WITH BREEZY WINDS
WHICH COULD GENERATE SOME HIGH SURF ALONG THE COASTLINE. ALONG
WITH WIND AND RAIN, IT LOOKS LIKE THE CASCADES COULD PICK UP
SOME DECENT EARLY SEASON SNOWFALL. DETAILS WILL BECOME MORE
REFINED AS WE GET CLOSER TO THE EVENT. TROUGHING LOOKS TO
DOMINATE THE PATTERN INTO THE WEEKEND, FOR PERIODS OF RAIN ALONG
WITH MOUNTAIN SNOW.
MAZURKIEWICZ
AVIATION
ZONAL FLOW ALOFT WILL WEAKEN AS A WEAK RIDGE AMPLIFIES
TONIGHT INTO TUESDAY OVER THE PACIFIC COAST. WINDS WILL DECREASE
THIS EVENING FROM SOUTHWEST 4-8 KT, DOWN TO LIGHT SOUTH WINDS UNDER
5 KT (SOME AREAS MAY SEE LIGHT-VARIABLE WINDS). THERE REMAINS HIGH
CONFIDENCE THAT A MARINE PUSH TONIGHT WILL BRING WIDESPREAD STRATUS
AND/OR FOG TO SEVERAL OF THE SOUTHERN TERMINALS TUESDAY MORNING
(BEGINNING ROUGHLY 10-13Z AND LASTING THROUGH 17-20Z). THE
PROBABILITY FOR FOG REMAINS HIGHEST IN THE SOUTH INTERIOR TUESDAY
MORNING (~30-40% CHANCE), WITH SOME UNCERTAINTY IN HOW FAR NORTHWARD
IT WILL REACH INTO PUGET SOUND (WHERE PROBABILITY IS HIGHER IN LOWER
STRATUS COMPARED TO THE FOG). ONCE FOG/STRATUS CLEARS, VFR
CONDITIONS WITH MOSTLY CLEAR SKIES ARE EXPECTED REST OF THE DAY.
WINDS WILL TURN NORTHERLY ACROSS MOST TERMINALS AROUND 17-19Z
TUESDAY 4-6 KT.
KSEA...VFR THROUGH TONIGHT (WITH CEILINGS CONTINUING TO LIFT THROUGH
THE EVENING AND PARTIALLY SCATTERING OUT). PROBABILITIES FOR LOW
STRATUS DOWN AT LIFR/IFR REMAIN HIGHER COMPARED TO THE CHANCE OF FOG
(25% COMPARED TO 15%) - WITH AGAIN SOME UNCERTAINTY AS TO HOW FAR
THE FOG WILL MAKE IT INLAND IN THE MORNING FROM THE SOUTHWEST.
EXPECTED TIMEFRAME FOR THE LOW CONDITIONS IS FROM 12-15Z TO 17-19Z.
CLEAR SKIES WILL FOLLOW IN THE AFTERNOON. WINDS THIS AFTERNOON
REMAIN OUT OF THE SOUTHWEST 4-8 KT - WILL DIMINISH TONIGHT BELOW 5
KT AND SWITCH TO NORTH 4-6 KT BY 17Z TUESDAY.
HPR/21
MARINE
A FEW BREEZY WIND GUSTS UP TO 20 KT REMAIN POSSIBLE
IN THE WEST STRAIT OF JUAN DE FUCA AREAS THROUGH TONIGHT, BUT
REMAINING AREAS WILL SEE LIGHT SOUTH WINDS SWITCH TO NORTH GOING
INTO TUESDAY AS HIGH PRESSURE BUILDS INLAND. SEAS WILL REMAIN
ELEVATED THROUGH LATE TUESDAY NIGHT - BUOYS IN THE COASTAL WATERS
CONTINUE TO SHOW SEAS AROUND 9 FT. A BRIEF DROP DOWN TO 7-9 FT IS
POSSIBLE THIS EVENING, BUT SEAS WILL BUILD AGAIN TOMORROW UP TO 10
TO 16 FT (WITH HIGHEST SEAS IN THE OUTER COASTAL WATERS). THE SMALL
CRAFT ADVISORY WAS EXTENDED TO 12Z WEDNESDAY TO REFLECT THE ELEVATED
SEAS. ADDITIONALLY, COULD SEE A FEW SPOTS IN THE SOUTH PUGET SOUND
WATERS WITH FOG EARLY TUESDAY MORNING.
A WEAK FRONT WILL PASS THROUGH ON WEDNESDAY, WITH MEDIUM CONFIDENCE
THAT PORTIONS OF THE INNER COASTAL WATERS AND STRAIT OF JUAN DE FUCA
AREAS SEEING A FEW GUSTS UP TO 25 KT. A STRONGER SYSTEM THURSDAY
INTO FRIDAY IS EXPECTED TO PRODUCE SIGNIFICANTLY STRONGER WINDS. AT
THIS TIME, THE PROBABILITY OF WATERS RECEIVING GALE WINDS IS VERY
HIGH (CLOSE TO 100% CHANCE OF SEEING GALE GUSTS ACROSS THE COASTAL
WATERS, STRAIT OF JUAN DE FUCA, NORTHERN INLAND WATERS AND ADMIRALTY
INLET AREAS). THERE IS ROUGHLY A 50-75% CHANCE THAT A FEW OF THE
GUSTS COULD REACH STORM FORCE (50 KT OR GREATER). SEAS ARE ALSO
EXPECTED TO BUILD BACK UP TO 15 TO 20 FT WITH THIS SYSTEM THROUGH
FRIDAY. ANY MARINERS TRAVELING ARE ENCOURAGED TO STAY TUNED FOR
POTENTIAL WATCHES AND WARNINGS WITH THIS SYSTEM.
THIS WEEKEND INTO NEXT WEEK ALSO WILL LIKELY REMAIN ACTIVE, WITH
WEST WINDS LIKELY REMAINING IN THE 25 TO 35 KT RANGE IN THE COASTAL
WATERS THROUGH THE WEEKEND. THE STRAIT MAY SEE ANOTHER ROUND OF
STRONGER GALES SATURDAY INTO MONDAY WITH LOWER CONFIDENCE IF GUSTS
WILL REACH GALES. COASTAL SEAS WILL REMAIN ABOVE 10 FT (UP TO 15 FT)
THROUGH THE WEEKEND INTO NEXT WEEK.
HPR/21
HYDROLOGY
A FRONTAL SYSTEM THAT WILL TAP INTO SOME SUBTROPICAL
MOISTURE WILL MOVE ACROSS WESTERN WASHINGTON LATE THURSDAY THROUGH
FRIDAY. RAINFALL AMOUNTS ARE FORECAST TO BE HEAVIEST OVER THE
OLYMPIC PENINSULA, WITH THE LATEST FORECAST SHOWING 2 TO 4 INCHES OF
PRECIPITATION OVER THE OLYMPICS THURSDAY EVENING THROUGH FRIDAY
AFTERNOON. RAINFALL AMOUNTS ARE EXPECTED TO BE LESS FOR THE
CASCADES, RANGING 1 TO 3 INCHES THROUGH FRIDAY EVENING. ALTHOUGH
PRECIPITATION IS EXPECTED TO CONTINUE AT TIMES SATURDAY INTO EARLY
NEXT WEEK, SNOW LEVELS WILL LOWER TO 3000 TO 4000 FEET BY LATER IN
THE WEEKEND. AT THIS TIME, CURRENT FORECASTS BRING THE SKOKOMISH
RIVER NEAR ACTION STAGE LATE FRIDAY. MODERATE TO HEAVY RAIN FRIDAY
MAY ALSO LEAD TO ROADWAY PONDING AND MINOR NUISANCE FLOODING OF POOR
DRAINAGE AREAS.
JD
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 5 AM PDT WEDNESDAY FOR COASTAL
WATERS FROM CAPE FLATTERY TO JAMES ISLAND 10 TO 60 NM-
COASTAL WATERS FROM CAPE FLATTERY TO JAMES ISLAND OUT 10
NM-COASTAL WATERS FROM JAMES ISLAND TO POINT GRENVILLE 10
TO 60 NM-COASTAL WATERS FROM JAMES ISLAND TO POINT
GRENVILLE OUT 10 NM-COASTAL WATERS FROM POINT GRENVILLE
TO CAPE SHOALWATER 10 TO 60 NM-COASTAL WATERS FROM POINT
GRENVILLE TO CAPE SHOALWATER OUT 10 NM-GRAYS HARBOR BAR-
WEST ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA.
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