Weather Service Report


755 
FXUS66 KSEW 270531
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
930 PM PST WED NOV 26 2014

.SYNOPSIS...A FRONT WILL MOVE EAST ACROSS WESTERN WASHINGTON TONIGHT 
FOR MORE RAIN AND WINDY CONDITIONS. RAIN WILL CONTINUE ON 
THANKSGIVING DAY AS A COLD FRONT APPROACHES FROM THE NORTH THEN 
CROSSES THE AREA ON FRIDAY. A COLD UPPER LEVEL TROUGH WILL MOVE 
OVER THE AREA FRIDAY NIGHT AND SATURDAY FOR A CHANCE OF 
SHOWERS...POSSIBLY MIXED WITH SNOW. COOLER AND DRY NORTHWEST FLOW 
ALOFT AND A SURFACE HIGH OVER BRITISH COLUMBIA WILL COMBINE FOR COOL 
DRY WEATHER AND MORE SUNSHINE SUNDAY THROUGH EARLY NEXT WEEK. 

&&

.SHORT TERM...CURRENT SATELLITE IMAGERY STILL SHOWS IMPENDING FRONT 
OFF THE COAST WITH TIMING ON FROPA REMAINING CONSISTENT...HITTING 
THE COAST AROUND OR JUST BEFORE MIDNIGHT AND OVER PUGET SOUND BEFORE 
12Z/4 AM. OBSERVED WINDS CONTINUING TO RAMP UP IN ADVANCE OF 
APPROACHING FRONT...THOUGH NOT QUITE HITTING ANTICIPATED LOW END 
ADVISORY SPEEDS JUST YET. SOME LOCATIONS ON THE NORTH COAST AND 
AROUND BLI ARE GETTING CLOSE. NO CHANGE IN EXPECTATION FOR WINDS TO 
EASE ONCE THE FRONT PASSES LATE TONIGHT. CURRENT RADAR SHOWS 
ACTIVITY ALONG THE CASCADES AND IN ADVANCE OF THE FRONT...LEAVING 
PUGET SOUND AND EAST PUGET LOWLANDS MOSTLY DRY FOR NOW. WILL EXPECT 
THAT HOLE TO FILL IN AS FRONT DRAWS CLOSER.

PICTURE FOR HOLIDAY WEEKEND REMAINS CONSISTENTLY WET. FOLLOWING 
FROPA TONIGHT...MAY CATCH A SLIGHT BREAK BEFORE SECOND FRONT MOVES 
SLOWLY OVER THE AREA THURSDAY AND INTO FRIDAY...BRINGING CONTINUED 
WET CONDITIONS. RAINFALL AMOUNTS EXPECTED OVER THE NEXT 48 HOURS IN 
A PERIOD STRETCHING FROM THIS EVENING THROUGH FRIDAY AFTERNOON RANGE 
FROM AROUND 1 TO 2 INCHES OF RAINFALL IN THE LOWLANDS AND 3 TO 6 
INCHES OF RAINFALL IN THE HIGHER ELEVATIONS OF THE CASCADES AND 
OLYMPICS. THE EXCEPTION BEING UP TO 7 INCHES OF RAINFALL AROUND MT. 
BAKER. NEEDLESS TO SAY...THIS AMOUNT OF RAINFALL WILL IMPACT RIVERS 
THAT HAVE ALREADY HIT FLOOD STAGE TODAY. EVEN THOUGH THESE RIVERS 
ARE TRENDING DOWNWARD WITH REGARD TO FLOW/LEVELS...THIS ADDITIONAL 
RAINFALL WILL LIKELY BRING ANOTHER PEAK IN FLOW/LEVELS FRIDAY. FOR 
FURTHER DETAILS...REFER TO THE HYDROLOGY SECTION BELOW.

MILD TEMPERATURES ARE EXPECTED TO REMAIN IN PLACE FOR THANKSGIVING 
BEFORE CONDITIONS BEGIN TO COOL. AN INTERESTING FORECAST CONUNDRUM 
ARISES FRIDAY NIGHT INTO SATURDAY. A DIPPING UPPER LEVEL TROUGH WILL 
BRING COLDER AIR TO WESTERN WASHINGTON FRIDAY NIGHT...JUST AT THE 
TAIL END OF PRECIP EVENT. GFS AND ECMWF INDICATE THAT THINGS MAY 
LINE UP JUST ENOUGH FOR MIXED LOWLAND PRECIP FRIDAY NIGHT WITH 
LOWLAND SNOW POSSIBLE SATURDAY. HOWEVER...LATEST RUN OF THE WRF GFS 
4KM DOES NOT LOOK AS CONVINCING AS THE OTHER TWO MODELS. INHERITED 
FORECAST HAS INCLUDED MENTIONS OF MIXED PRECIP AND SNOW FOR THIS 
TIME FRAME AND WILL ALLOW FOR FURTHER REEXAMINATION WITH FUTURE 
MODEL RUNS. SMR

.LONG TERM...FROM 410 PM DISCUSSION...A STRONG SURFACE HIGH SETTLING 
OVER B.C. ON FRIDAY WILL ALLOW COLD FRASER RIVER VALLEY OUTFLOW TO 
DEVELOP...BRINGING MORE COLD AIR DRY S OVER W WA. THE AIR MASS WILL 
DRY OUT SATURDAY NIGHT WITH TEMPERATURES DROPPING INTO THE 20S 
SUNDAY MORNING. SKIES WILL BE MOSTLY SUNNY. THE FRASER VALLEY 
OUTFLOW WILL PROBABLY GENERATE ADVISORY LEVEL NE WINDS OVER WHATCOM 
AND SAN JUAN COUNTY FRIDAY NIGHT INTO SATURDAY MORNING. 

THE ECMWF HAS LEANED MORE CONSISTENTLY THAN THE GFS IN KEEPING A 
COOL DRY PATTERN OVER W WA INTO EARLY NEXT WEEK. THE LATEST ECMWF 
NOW KEEPS THE PATTERN DRY THROUGH WEDNESDAY ALTHOUGH THERE ARE 
SYSTEM THAT GET CLOSE. THE GFS HAD BEEN MORE AGGRESSIVE IN BRINGING 
RAIN UP OVER THE ARE FROM THE S...BUT HAS BACKED AWAY FROM THIS ON 
THE 12Z AND 18Z RUNS. IT MAY HAVE BEEN PREMATURE...BUT I HAVE DRIED 
OUT EARLY NEXT WEEK. CONFIDENCE IS SHAKY BUT HOPE IT STAYS THAT WAY. 
KAM

&&

.HYDROLOGY...FROM 410 PM DISCUSSION...A WARM FRONT HELD HEAVIER 
RAINFALL NORTH OF THE WA/BRITISH COLUMBIA BORDER TODAY. THIS IS 
ALLOWING MOST RIVERS TO SLOWLY RECEDE ACROSS WRN WA. RAIN AMOUNTS UP 
TO 5 INCHES SINCE MONDAY IN PLACES LIKE MOUNT RAINIER AND THE 
SKYKOMISH-SNOQUALMIE-TOLT-SNOHOMISH BASIN WILL STILL CAUSE SOME 
RESIDUAL FLOODING...MAINLY THROUGH THIS EVENING. 

ANOTHER FRONT WILL BRING RENEWED RAINFALL TO WRN WA TONIGHT AND 
THURSDAY...LOCALLY HEAVY IN THE MOUNTAINS. THE OLYMPICS AND NORTH 
CASCADES WILL RECEIVE THE HEAVIEST RAINFALL WITH 2 TO 4 INCHES OF 
RAIN EXPECTED. 1 TO 2 INCHES MAY FALL IN THE CENTRAL CASCADES. THE 
SNOW LEVEL WILL BE NEAR 7000 FEET.

A SECONDARY SURGE OF MOISTURE WILL ARRIVE THURSDAY NIGHT INTO 
FRIDAY. MODELS VARY MUCH MORE ON THE DISTRIBUTION AND POTENTIAL 
RAINFALL AMOUNTS WITH THIS SECOND FRONTAL SYSTEM. IN 
GENERAL...HEAVIER RAIN AMOUNTS THURSDAY NIGHT AND FRIDAY SHOULD 
OCCUR ALONG S/SW FACING SLOPES OF THE OLYMPICS AND N 
CASCADES...ALTHOUGH THE CENTRAL CASCADES COULD ALSO SEE HEAVY 
PRECIPITATION BY FRIDAY. ADDITIONAL AMOUNTS OF 2 TO 3 INCHES ARE 
POSSIBLE. THIS MEANS THE 36-48 HOUR RAINFALL TOTALS FOR THE OLYMPICS 
AND CASCADES MAY REACH 4 TO 7 INCHES WITH LOCALLY HIGHER 
AMOUNTS...ESPECIALLY IN THE N CASCADES. 

THESE AMOUNTS WILL LIKELY DRIVE SEVERAL RIVERS TO FLOOD...ALTHOUGH 
WIDESPREAD MAJOR FLOODING APPEARS UNLIKELY. AT HIGHEST RISK FOR 
FLOODING IS THE SKOKOMISH RIVER IN THE OLYMPICS...THE NOOKSACK AND 
SKAGIT RIVERS IN THE NORTH...AND THE 
STILLAGUAMISH...SNOQUALMIE...AND TOLT ACROSS CENTRAL AREAS. IF THE 
HEAVIER RAIN SHIFTS FAR ENOUGH SOUTH THEN FLOODING COULD BE POSSIBLE 
ON THE DESCHUTES RIVER AND THE REACH OF THE SKOOKUMCHUCK RIVER NEAR 
BUCODA IN THURSTON COUNTY.

A FLOOD WATCH REMAINS IN EFFECT THROUGH FRIDAY...WHICH INCLUDES ALL 
THE COUNTIES WITH RIVERS FLOWING OFF THE WEST SLOPES OF THE CASCADES 
AND MASON COUNTY FOR THE POSSIBILITY OF A FLOOD ON THE SKOKOMISH.

COLDER AND DRIER WEATHER IS LIKELY THIS WEEKEND...SO RIVERS SHOULD 
RECEDE AND THE FLOOD THREAT WILL END FOR THE FORESEEABLE FUTURE.   

MERCER

&&

.AVIATION...RAIN IN INCREASE IN COVERAGE ACROSS WESTERN WA TONIGHT 
AS A COLD FRONT MOVES INLAND. THE FLOW ALOFT IS WESTERLY. CIGS ARE 
MAINLY VFR THIS EVENING BUT SHOULD LOWER INTO MVFR RANGE OVERNIGHT. 
GUSTY SOUTH WINDS ARE ALSO EXPECTED WITH THE FRONT...ESPECIALLY 
ALONG THE COAST AND NORTH INTERIOR. MOIST WESTERLY FLOW WILL 
CONTINUE ON THURSDAY WITH SHOWERS MAINLY AFFECTING THE COAST AND 
MOUNTAINS. 33

KSEA...EXPECT RAIN AT TIMES TONIGHT WITH CIGS LOWERING TO MVFR 
RANGE. GUSTY SOUTH WINDS 20015G25KT EXPECTED AT THE TERMINAL 
THROUGHOUT THE NIGHT. 33

&&

.MARINE...A COLD FRONT WILL SHIFT INLAND TONIGHT WITH INCREASING 
SOUTH WINDS OVER THE WATERS. GALE WARNINGS REMAIN IN EFFECT FOR THE 
COASTAL WATERS...ENTRANCES TO THE STRAIT OF JUAN DE FUCA AND THE 
NORTHERN INLAND WATERS. A GALE WARNING WAS ALSO ISSUED FOR ADMIRALTY 
INLET. WINDS WILL EASE OVERNIGHT BUT WILL STILL SEE SMALL CRAFT 
ADVISORY WINDS ACROSS THE WATERS. PRESSURE GRADIENTS WILL REMAIN 
TIGHT THU NIGHT THROUGH FRI AS ANOTHER COLD FRONT PUSHES SOUTH FROM 
B.C. STRONG HIGH PRES OVER INTERIOR B.C. WILL BRING N/NE FRASER 
RIVER OUTFLOW WINDS LATE FRI NIGHT INTO SAT. OFFSHORE FLOW WILL 
PREVAIL SUN AND MON WITH HIGH PRES EAST OF THE CASCADES. 33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WATCHES AND WARNINGS IN EFFECT FOR PORTIONS OF            
     WESTERN WASHINGTON.
     WIND ADVISORY NORTH COAST...WESTERN WHATCOM...SAN               
     JUANS...ADMIRALTY INLET AREA. 

PZ...SMALL CRAFT ADVISORY ALL WATERS.
    .SMALL CRAFT ADVISORY GRAYS HARBOR BAR FOR ROUGH BAR.
    .GALE WARNING COASTAL WATERS...ENTRANCES STRAIT OF JUAN DE       
     FUCA...NORTHERN INLAND WATERS...ADMIRALTY INLET.

&&

$$

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