Flood Watch 11, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
330 PM PST FRI NOV 25 2011

.SYNOPSIS...A WARM FRONT WILL BRING MORE RAIN AND WINDY CONDITIONS
TO THE AREA LATE TONIGHT THROUGH SATURDAY. A COLD FRONT WILL SLIDE
SOUTHEAST THROUGH THE AREA ON SUNDAY. DRY WEATHER WILL RETURN FOR
THE START OF THE WORK WEEK.

&&

.SHORT TERM...OVERALL SEEMED LIKE A PRETTY DECENT DAY ACROSS WESTERN
WA. SKIES REMAINED PARTLY TO MOSTLY SUNNY ACROSS MOST SPOTS. BUT WE
ARE IN FOR A CHANGE IN THE WEATHER THIS WEEKEND WITH ANOTHER ROUND
OF BLUSTERY WINDS...RAIN AND POSSIBLE RIVER FLOODING.

A WARM FRONT WILL CLIP WESTERN WA TONIGHT THROUGH SAT WITH RAIN
MAINLY AFFECTING THE COAST...OLYMPICS AND NORTH CASCADES. WILL
INCLUDE CHANCE POPS IN THE INTERIOR BUT RAIN TOTALS ARE LIGHT...ONLY
A FEW HUNDREDTHS IF ANYTHING. SE PRES GRADIENTS INCREASE AS THE
FRONT STALLS OVER B.C. SAT NIGHT. VERY WINDY CONDITIONS ARE EXPECTED
ALONG THE COAST AND NORTH INTERIOR WITH DAMAGING WINDS POSSIBLE.
WILL ISSUE A HIGH WIND WATCH FOR THESE ZONES. THE AIR MASS WILL FEEL
QUITE MILD ON SAT AS WE LIE IN THE WARM SECTOR. FORECAST HIGHS ARE
IN THE LOWER TO MID 50S...WITH SNOW LEVELS AROUND 7000 FEET AGL. THE
COLD FRONT /BAROCLINIC ZONE/ WILL SLIDE SE THROUGH W WA ON
SUN...LIKELY OUR WETTEST PERIOD OF WEATHER THIS WEEKEND. THE FLOW
WILL QUICKLY TURN TO W/NW BEHIND THE FRONT WITH STRONG WEST WINDS
THROUGH THE STRAIT. MAY NEED TO WATCH FOR STRONG WINDS IN ADMIRALTY
INLET AREA /WHIDBEY ISLAND/. FOR THE PRECIP...THE OLYMPICS AND
CASCADES WILL SEE SEVERAL INCHES OF PRECIP WITH STRONG OROGRAPHICS.
THE RIVERS ARE STILL SWOLLEN FROM OUR LAST RECENT EVENT AND LOOKS
LIKE SOME RIVER FLOODING IS POSSIBLE. A FLOOD WATCH IS IN EFFECT FOR
MASON...WHATCOM AND SNOHOMISH COUNTIES. SEE HYDROLOGY DISCUSSION
BELOW.

THE COLD FRONT WILL EXIT SUN NIGHT WITH SHOWERS TAPERING DOWN ACROSS
WESTERN WA. DRY WEATHER WILL RETURN FOR MONDAY WITH WEAK RIDGING
OVER THE PAC NW. 33

.LONG TERM...THE PAC NW WILL REMAIN DRY THROUGH TUE WITH FLAT
RIDGING OVER THE REGION. MODELS SHOW A SHORT WAVE TROUGH QUICKLY
CLIPPING THROUGH W WA TUE NIGHT OR POSSIBLY WED. THE EURO IS A BIT
SLOWER AND WETTER THAN THE GFS. BUT OVERALL THIS SYSTEM IS LOOKING
RATHER WEAK. A STRONG UPPER LEVEL RIDGE WILL BUILD OVER THE NE PAC
THROUGH THE END OF THE WEEK...BRINGING ANOTHER EXTENDED PERIOD OF
DRY WEATHER. POPS WERE REDUCED ACROSS THE BOARD. 33

&&

.HYDROLOGY...THE NEXT FRONTAL SYSTEM WILL AFFECT THE REGION LATE
TONIGHT THOUGH SUNDAY. IT HAS THE POTENTIAL TO CAUSE NEW FLOODING ON
THE SKOKOMISH...NOOKSACK...AND POSSIBLY STILLAGUAMISH RIVERS.
FLOODING IS UNLIKELY ON OTHER RIVERS.

MODEL QPF FROM THE NAM AND GFS 12Z RUNS WERE NOT IN GOOD AGREEMENT
WITH THE NAM CONSIDERABLY WETTER THAN THE GFS. THE 18Z RUNS HAVE
CONVERGED A BIT BUT BOTH ARE SHOWING LESS RAIN THAN IN EARLIER RUNS.
THE NWS RIVER FORECAST CENTER RIVER MODEL SHOWED BOTH THE SKOKOMISH
RIVER AND THE NOOKSACK RIVER NEAR NORTH CEDARVILLE GETTING JUST
ABOVE FLOOD STAGE. THE INPUT TO THE MODEL WAS QPF AT THE WETTER END
OF THE POSSIBLE SOLUTIONS. THE MODEL ALSO SHOWED THE STILLAGUAMISH
RIVER GETTING CLOSE TO FLOOD STAGE.

WILL ISSUE A FLOOD WATCH THIS AFTERNOON FOR THE THREE COUNTIES
CONTAINING THOSE BASINS. ANY FLOODING IS LIKELY TO BE MINOR AND WILL
NOT START UNTIL SUNDAY OR SUNDAY NIGHT. BURKE

&&

.AVIATION...HIGH CLOUDS ARE INCREASING OVER WESTERN WASHINGTON THIS
AFTERNOON AS A WARM FRONT APPROACHES THE COAST IN STRONG WESTERLY
FLOW ALOFT. LANGLEY HILL RADAR ALREADY SHOWS ECHOES OFF THE COAST.
AIR MASS STABLE WITH INCREASING MOISTURE ALL LEVELS BY MORNING.
STRONG SOUTHEASTERLY GRADIENTS WILL DEVELOP TONIGHT OVER MOST AREAS
BUT NOT CENTRAL PUGET SOUND. RAIN LIKELY SATURDAY AS THE WARM FRONT
MOVES INLAND.

KSEA...INCREASING HIGH CLOUDS TONIGHT WILL KEEP CEILINGS VFR BUT BY
SATURDAY MORNING SOME MVFR IS POSSIBLE IN LIGHT RAIN. WINDS
SOUTHERLY 4-8 KT TONIGHT...INCREASING TO 8-12 KT SATURDAY. CHB

&&

.MARINE...STRONG WINDS ARE LIKELY TONIGHT THROUGH SUNDAY AS A WARM
FRONT AND THEN A COLD FRONT MOVE THROUGH THE AREA. WINDS WILL BE
SOUTHEAST OVER MOST ZONES BEFORE TURNING MORE ONSHORE SUNDAY
AFTERNOON. GALE WARNINGS ARE UP OVER ALL THE ZONES THAT ROUTINELY
GET SOUTHEAST GALES...WITH ONLY PUGET SOUND AND THE CENTRAL STRAIT
FORECAST TO REMAIN SUB-GALE.

THE WESTERLIES SUNDAY AFTERNOON IN THE STRAIT COULD ALSO BE GALE
FORCE BUT HAVE KEPT THEM 20-30 KT FOR NOW.

GRADIENTS SUBSIDE EARLY NEXT WEEK FOR AT LEAST A COUPLE OF QUIET
DAYS. CHB

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...HIGH WIND WATCH COAST AND NORTH INTERIOR.

PZ...GALE WARNING ALL WATERS EXCEPT PUGET SOUND AND CENTRAL STRAIT.
     SMALL CRAFT ADVISORY FOR CENTRAL STRAIT.
     SMALL CRAFT ADVISORY FOR SEVERE GRAYS HARBOR BAR.

YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML.

WWW.WEATHER.GOV/SEATTLE