637
FXUS66 KSEW 232247
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
347 PM PDT WED SEP 23 2020
SYNOPSIS
A SERIES OF VIGOROUS FRONTAL SYSTEMS WILL BRING WET
AND WINDY WEATHER ALONG WITH COOLER TEMPERATURES THROUGH THE
WEEKEND. HIGH PRESSURE ALOFT REBUILDS OVER THE REGION EARLY NEXT
WEEK FOR A RETURN OF DRY AND WARMER WEATHER.
SHORT TERM /TONIGHT THROUGH SATURDAY/
DEEP PLUME OF MOISTURE
REMAINS CENTERED OVER WESTERN WASHINGTON THIS MORNING, WITH THE
STEADIEST PRECIPITATION ALIGNED ROUGHLY FROM OCEAN SHORES TO
BELLINGHAM AT THIS HOUR. LATEST NWS RADAR DATA INDICATE THAT THE
NEXT BIT OF STEADIER RAIN IS MAKING A PUSH INTO THE KITSAP
PENINSULA AND INTO THE SEATTLE METRO AREA IN TIME FOR THE EVENING
COMMUTE. BEHIND THIS LINE, FAIRLY WIDESPREAD SHOWERS ARE ALSO
DEVELOPING. SO FAR, STATIONS ON THE SOUTHERN AND WESTERN PORTIONS
OF OLYMPIC PENINSULA HAVE RANGED GENERALLY FROM 2 TO 4 INCHES OF
RAIN. MEANWHILE, PLENTY OF SHOWERS CONTINUE TO DEVELOP BEHIND THE
MAIN RAIN SHIELD. THE ENVIRONMENT REMAINS SOMEWHAT UNSTABLE BEHIND
THE FRONT, WITH A MORE CONVECTIVE APPEARANCE IN THE DEVELOPING
SHOWERS OVER THE COASTAL WATERS. LIGHTNING HAS BEEN DETECTED IN
THESE STORMS WELL OFFSHORE AND STORMS HAVE BEEN MANAGING TO HOLD
TOGETHER. WILL NEED TO CONTINUE TO KEEP A CLOSE EYE ON RADAR
TRENDS INTO THE EVENING AND OVERNIGHT HOURS. MEANWHILE THE
HEAVIEST RAIN WILL CONTINUE TO SHIFT SOUTH OVERNIGHT.
EXPECT CONTINUED SHOWERS ACROSS THE REGION, WITH THE HIGHEST
AMOUNTS IN THE MOUNTAINS AS FLOW BECOMES INCREASING WESTERLY.
WHILE INSTABILITY LOOKS TO BE SOMEWHAT MODEST, THE OVERALL
ENVIRONMENT MAY CONTINUE TO SUPPORT SOME STRONG SHOWERS AND
THUNDERSTORMS. THE NEXT FRONTAL SYSTEM APPROACHES LATE THURSDAY
AND MOVES ACROSS THE AREA EARLY FRIDAY, WITH ANOTHER ROUND OF
RAIN LIKELY. LATEST GUIDANCE KEEPS THIS SYSTEM MOVING THROUGH
RATHER QUICKLY, BUT EXPECT SOME BREEZY WINDS ACROSS THE AREA
FRIDAY MORNING AS IT DOES SO. PLENTY OF SHOWERS FOLLOW BEHIND WITH
ANOTHER SHORTWAVE IMPULSE CROSSING ON SATURDAY TO PROVIDE FOR EVEN
MORE RAIN. ALL TOGETHER, ANOTHER 2 INCHES OF RAIN IN THE LOWLANDS
AND 4-7 INCHES IN MOUNTAINS (LOCALLY HIGHER AMOUNTS IN THE FAVORED
TERRAIN) ARE EXPECTED THURSDAY THROUGH LATE SATURDAY NIGHT.
CULLEN
LONG TERM /SUNDAY THROUGH WEDNESDAY/
RAIN FROM THE WEEKEND
SYSTEM WILL BEGIN TO TAPER OUT THROUGHOUT SUNDAY. ENSEMBLES ARE
SUGGESTING THAT IT MAY LINGER IN THE NORTHERN WASHINGTON AREA
THROUGH MONDAY BUT AS OF RIGHT NOW THERE IS ONLY A SLIGHT CHANCE
FOR THAT TO OCCUR. BY TUESDAY THAT UPPER LEVEL RIDGE SHOULD BE
DIRECTLY OVER US, AND WITH A SURFACE TROUGH OFF THE COAST OFFSHORE
FLOW IS LIKELY TO OCCUR. THIS WILL CERTAINLY DRY THINGS OUT AND
BRING WARMER TEMPERATURES TO THE AREA. HIGHS IN THE MID 70S ARE
CERTAINLY POSSIBLE FOR THE LOW LYING AREAS OF WESTERN WASHINGTON
COME TUESDAY AND WEDNESDAY, MID TO UPPER 60S BY THE COAST AND
HIGHER ELEVATION'S. LOOKING AHEAD, ECMWF, GFS AND CMC ENSEMBLE
GUIDANCE HAS THIS UPPER LEVEL RIDGE STICKING AROUND OUR AREA FOR
THE START OF OCTOBER.
BUTWIN
AVIATION
AN EARLY FALL STORM SYSTEM WILL BRING WIDESPREAD RAIN TO
THE TERMINALS THROUGH THE TAF PERIOD. AS THE RAIN CONTINUES TO
SPREAD EAST, EXPECT ALL TERMINALS TO BE AFFECTED, WITH CEILINGS
DROPPING TO AT LEAST MVFR (PERHAPS IFR AT TIMES), THROUGH THE DAY
TODAY WITH LITTLE RECOVERY. IFR VISIBILITY WILL ALSO BE POSSIBLE
WITHIN AREAS OF HEAVIER RAIN. RAIN WILL EVENTUALLY TAPER TO SHOWERS
OVERNIGHT TONIGHT INTO THURSDAY. WINDS WILL NOTICEABLY PICK UP TODAY
OUT OF THE SOUTH, SUSTAINED GENERALLY BETWEEN 10 TO 20 MPH WITH
GUSTS 20 TO 30 MPH (COULD BE LOCALLY HIGHER AT A FEW SITES ALONG THE
COAST). WINDS WILL EASE LATE WEDNESDAY NIGHT INTO THURSDAY BEFORE
COMING UP AGAIN IN THE MORNING HOURS OF FRIDAY BEFORE TAPERING.
KSEA
MVFR CONDITIONS AT THE TERMINAL AS RAIN CONTINUES TO
MOVE INTO THE AREA. RAIN SHOWERS WILL CONTINUE TO FILL IN THROUGH
THE DAY. WINDS SOUTH SUSTAINED 10-20 MPH WITH GUSTS AROUND 25 MPH
BEGINNING THIS AFTERNOON AND LASTING THROUGH THE NIGHT.
KRISTELL
MARINE
A SERIES OF ROBUST FRONTAL SYSTEMS WILL AFFECT THE WATERS
OVER THE NEXT SEVERAL DAYS. RAIN WILL CONTINUE EAST THROUGH MOST OF
THE DAY AND OVERNIGHT HOURS, WITH WINDS ALSO PICKING UP AS FRONT
PROGRESSES INLAND. CURRENT HEADLINES REMAIN IN PLACE WITH GALE FORCE
WINDS EXPECTED OVER THE COASTAL WATERS/WESTERN STRAIT OF JUAN DE
FUCA AND THE NORTHERN INLAND WATERS/EASTERN STRAIT OF JUAN DE FUCA,
AND ADMIRALTY INLET. ELSEWHERE, SMALL CRAFT ADVISORY LEVEL WINDS ARE
EXPECTED. WINDS WILL GRADUALLY EASE THROUGH THE OVERNIGHT HOURS INTO
THURSDAY AS THE FRONT PASSES, HOWEVER, SHOWER ACTIVITY WILL PERSIST.
CURRENT SATELLITE IMAGERY SHOWS THUNDERSTORMS MOVING ALONG THE MAIN
FRONTAL BAND IN THE OFFSHORE WATERS, WHICH MAY CONTINUE MOVING EAST
TO IMPACT COASTAL LOCATIONS THIS EVENING.
WAVES WILL INCREASE OVER THE COASTAL WATERS WITH THE FRONTAL SYSTEM
TODAY, GENERALLY TO BETWEEN 10-12 FEET. A MORE SIGNIFICANT SWELL IS
LIKELY ON THURSDAY WITH WAVES BUILDING TO BETWEEN 14-16 FEET. A HIGH
SURF ADVISORY HAS BEEN ISSUED FOR THE COAST BEGINNING ON THURSDAY.
WAVES WILL CONTINUE INTO FRIDAY BEFORE FINALLY SUBSIDING TO 10-13
FEET.
ADDITIONAL FRONTAL SYSTEMS WILL AFFECT THE WATERS THROUGH THE
REMAINDER OF THE WEEK AND THROUGH MUCH OF THE WEEKEND. PERIODS OF
ELEVATED WINDS AND AGITATED SEAS CAN BE EXPECTED.
KRISTELL
HYDROLOGY
SHARP RISES ARE ANTICIPATED ON SEVERAL RIVERS AND
STREAMS FLOWING FROM THE SOUTHERN OLYMPICS (INCLUDING THE
SKOKOMISH) AND PORTIONS OF THE CASCADES. THE FOCUS OF HEAVIEST
RAIN WILL BEGIN TO SHIFT SOUTH TONIGHT. THE FASTER RESPONDING
RIVERS MAY RECEDE A BIT ON THURSDAY AS STEADY RAIN TRANSITIONS TO
SHOWERS. HOWEVER, ADDITIONAL HEAVY RAINFALL FRIDAY AND SATURDAY
COULD BRING ADDITIONAL RISES TO MANY RIVERS - PARTICULARLY THOSE
DRAINING FROM THE OLYMPICS AND NORTH CASCADES, THOUGH POSSIBLY
ELSEWHERE, TOO. AN ADDITIONAL 4-7 INCHES OF RAIN IS EXPECTED IN
THE MOUNTAINS THURSDAY THROUGH THE END OF THE WEEKEND, BEFORE A
SHIFT TO A DRIER PATTERN DEVELOPS EARLY NEXT WEEK.
SEW WATCHES/WARNINGS/ADVISORIES
WA...WIND ADVISORY UNTIL 5 PM PDT THIS AFTERNOON FOR CENTRAL COAST-
NORTH COAST.
HIGH SURF ADVISORY FROM 11 AM THURSDAY TO 2 PM PDT FRIDAY FOR
CENTRAL COAST-NORTH COAST.
PZ...GALE WARNING UNTIL 6 PM PDT THIS EVENING FOR ADMIRALTY INLET-
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-EAST ENTRANCE U.S.
WATERS STRAIT OF JUAN DE FUCA-NORTHERN INLAND WATERS
INCLUDING THE SAN JUAN ISLANDS.
SMALL CRAFT ADVISORY UNTIL 11 PM PDT THURSDAY FOR GRAYS HARBOR
BAR.
SMALL CRAFT ADVISORY UNTIL 6 PM PDT THIS EVENING FOR CENTRAL
U.S. WATERS STRAIT OF JUAN DE FUCA-WEST ENTRANCE U.S.
WATERS STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY UNTIL 8 PM PDT THIS EVENING FOR PUGET SOUND
AND HOOD CANAL.
WWW.WEATHER.GOV/SEATTLE
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