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.  
 

 
 

 
 
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