Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 281051
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
350 AM PDT TUE OCT 28 2014

.SYNOPSIS...A FRONTAL SYSTEM WILL MOVE THROUGH THE AREA THIS
MORNING. HIGH PRESSURE ALOFT WILL BUILD OVER THE AREA ON WEDNESDAY
FOR A MOSTLY DRY DAY. A SECOND FRONT WILL BRING ANOTHER ROUND OF
RAIN BEGINNING WEDNESDAY NIGHT OVER THE SOUTHERN PORTION OF THE AREA
WITH THE RAIN SPREADING NORTH ON THURSDAY. WET WEATHER WILL CONTINUE
INTO EARLY NEXT WEEK AS ADDITIONAL WEATHER SYSTEMS MOVE THROUGH.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS COLD FRONT ALONG 126W EARLY
THIS MORNING MOVING EASTWARD WITH A WARM FRONT OVER THE AREA LIFTING
NORTH. DOPPLER RADARS AND SURFACE OBSERVATIONS SHOW RAIN OVER MOST
OF THE AREA AT 10Z/3AM. TEMPERATURES WERE IN THE UPPER 40S TO MID
50S.

COLD FRONT MOVING THROUGH WESTERN WASHINGTON THIS MORNING WITH THE
STEADY RAIN GIVING WAY TO SHOWERS BEHIND THE FRONT. WINDY CONDITIONS
OVER THE NORTHWEST INTERIOR...OBSERVATIONS FROM NAS WHIDBEY AND IN
THE SAN JUANS REPORTING GUSTS 30-40 MPH AT 3 AM...WILL EASE BEHIND
THE FRONT. WILL KEEP THE WIND ADVISORY GOING FOR THE NORTHWEST
INTERIOR UNTIL 8 AM THIS MORNING. WINDS WILL PICK UP OVER THE
REMAINDER OF THE INTERIOR WITH AND BEHIND THE FRONT WITH BREEZY
CONDITIONS EXPECTED LATER THIS MORNING INTO THE AFTERNOON HOURS.
HIGH TEMPERATURES WILL BE IN THE MID 50S TO LOWER 60S.

SOUTHWESTERLY FLOW ALOFT CONTINUING OVER WESTERN WASHINGTON TONIGHT
WITH SHOWERS EMBEDDED IN THE FLOW ALOFT MOVING THROUGH THE AREA.
WINDS EASING OVERNIGHT AS SURFACE PRESSURE GRADIENTS DECREASE. LOWS
WILL BE MOSTLY IN THE UPPER 40S TO MID 50S.

SHOWER ACTIVITY DECREASING WEDNESDAY MORNING AS A WEAK RIDGE OF HIGH
PRESSURE BUILDS INTO WESTERN WASHINGTON AND SURFACE PRESSURE
GRADIENTS GO OFFSHORE IN RESPONSE TO THE NEXT APPROACHING WEATHER
SYSTEM. STILL A FEW LINGERING SHOWERS WEDNESDAY MORNING WITH THE
BEST CHANCES FOR SHOWERS IN THE MOUNTAINS. HIGHS ON WEDNESDAY WILL
BE NEAR 60 DEGREES.

SOUTHWESTERLY FLOW ALOFT INCREASING AGAIN WEDNESDAY NIGHT INTO
THURSDAY WITH ANOTHER FRONTAL SYSTEM MOVING INTO THE AREA LATE
THURSDAY. THIS SYSTEM WILL ONCE AGAIN HAVE A BIT OF A SUB TROPICAL
TAP TO IT SO THERE IS THE POTENTIAL FOR ANOTHER ROUND OF SIGNIFICANT
RAINFALL ESPECIALLY OVER THE SOUTH SLOPES OF THE OLYMPICS. SURFACE
PRESSURE GRADIENTS WILL TIGHTEN UP ON THURSDAY RESULTING IN BREEZY
CONDITIONS ACROSS THE CWA. HIGHS WILL ONCE AGAIN BE NEAR 60 DEGREES.

.LONG TERM...EXTENDED MODELS IN FAIRLY GOOD AGREEMENT EARLY ON IN
THE PERIOD WITH THE UPPER LEVEL TROUGH OFFSHORE DIGGING SOUTH
STALLING THE FRONT OVER WESTERN WASHINGTON THURSDAY NIGHT. UPPER
LEVEL TROUGH OFFSHORE MOVES EAST ON FRIDAY PUSHING WHAT IS LEFT OF
THE FRONT INTO EASTERN WASHINGTON BUT WITH THE TROUGH STILL OFFSHORE
SHOWERS WILL REMAIN IN THE FORECAST. TROUGH AXIS MOVING THROUGH
FRIDAY NIGHT INTO SATURDAY MORNING WITH THE BEST CHANCE FOR A BREAK
IN THE PRECIPITATION AT THIS POINT SATURDAY AFTERNOON. NEXT SYSTEM
TO REACH THE AREA MOVING DOWN FROM THE NORTHWEST SATURDAY NIGHT INTO
SUNDAY FOR ANOTHER ROUND OF RAIN. SOME DIFFERENCES BEGINNING TO SHOW
UP IN THE MODELS ON MONDAY WITH THE ECMWF BUILDING A WEAK RIDGE OVER
THE AREA WHILE THE GFS KEEPS THE ZONAL FLOW INTACT WITH YET ANOTHER
SYSTEM MOVING INTO THE AREA. FOR NOW WILL STAY WITH THE LIKELY POPS
FOR MONDAY. FELTON

&&

.HYDROLOGY...RAINFALL AMOUNTS OVER THE SOUTH SLOPES OF THE OLYMPICS
HAVE NOT BEEN TOO IMPRESSIVE SO FAR WITH ABOUT ONE HALF TO 0.85 IN
THE LAST SIX HOURS. RAINFALL RATES HAVE INCREASED IN THE LAST THREE
HOURS. HYDROGRAPHS SHOW THE FORKS OF THE SKOKOMISH STARTING TO RISE
IN THE LAST COUPLE OF HOURS. HEAVIEST RAINFALL IS EXPECTED IN THE
NEXT FEW HOURS AHEAD AND WITH THE FRONT. WILL STAY WITH THE FLOOD
WATCH FOR THE SKOKOMISH FOR TODAY WITH THE POSSIBILITY OF THE RIVER
GOING OVER FLOOD STAGE LATER THIS AFTERNOON INTO THIS EVENING.

ON ALL OTHER RIVERS FLOODING IS UNLIKELY OVER THE NEXT 7 DAYS.
FELTON

&&

.AVIATION...A STRONG WARM FRONT IS OVER W WA THIS MORNING WITH
WIDESPREAD RAIN. THE ASSOCIATED WEAKER COLD FRONT IS JUST OFFSHORE
AND WILL MOVE INLAND THIS MORNING. AN UPPER LEVEL TROUGH WILL REMAIN
OVER THE AREA THIS AFTERNOON WHILE THE SURFACE FRONTS WEAKEN.

CIGS ARE BEGINNING TO LOWER DUE TO WIDESPREAD RAIN...BUT STILL
REMAIN VFR IN MOST AREAS. MVFR CIGS ARE STILL EXPECTED TO DEVELOP
AFTER 12Z WITH IFR CIGS ON THE COAST AND SPOTTY IFR OVER PARTS OF
THE INTERIOR. VISIBILITY WILL LOWER TO LOCALLY 3-5SM IN RAIN AT
TIMES THIS MORNING. ONLY SLIGHT IMPROVEMENT IS EXPECTED THIS
AFTERNOON WHILE THE FRONTS WEAKEN AND SHOWERS TRAVERSE THE
AREA...MORE AREAS WILL BE VFR BKN-OVC030-050 AND FEWER LOCATIONS
WILL HAVE MVFR CIGS. SHOWERS ARE EXPECTED THIS AFTERNOON. BREEZY
SOUTHERLY WINDS 10-20G25KT WILL BE COMMON.

KSEA...CONTINUING RAIN FROM THE WARM FRONT OVER THE AREA AND THE
WEAKER COLD FRONT EXPECTED TO MOVE INLAND THIS MORNING...WILL LOWER
CIGS DOWN TO OVC020-030 THIS MORNING. VISIBILITY MAY DROP DOWN TO
3-5SM AT TIMES DUE TO THE RAIN. SLIGHT IMPROVEMENT TO VFR CIGS AND
VISIBILITY IS EXPECTED AFTER 18Z...BUT CIGS WILL REMAIN IN THE
030-050 RANGE. SURFACE WINDS WILL SHIFT FROM SE TO S AND RISE TO
10-15KT WITH GUSTS TO 22 KT POSSIBLE. KAM

&&

.MARINE...A WARM FRONT APPEARS TO BE MOVING ACROSS W WA EARLY THIS
MORNING...AND IR IMAGERY SHOWS THE COLD FRONT STILL JUST W OF THE
COAST. THE HARO STRAIT OB IS RUNNING RIGHT NEAR GALE FORCE SO THERE
IS SOME CONFIDENCE THAT THE GALES WILL STILL WORK OUT. BIT HARDER TO
TELL NOW THAT SOME KEY OBS ARE ON THE INJURY REPORT. I WILL LET THE
GALES EXPIRE AS PLANNED...6 AM FOR THE COAST...10 AM FOR THE
INTERIOR...WITH ALL BEING REPLACED BY ADVISORIES.

ONCE THE WARM FRONT IS THROUGH...WINDS SHOULD BEGIN DIMINISHING AS
THE WEAKER COLD FRONT MOVES INLAND. THE MAIN FEATURE THIS AFTERNOON
AND EVENING WILL BE THE PARENT SURFACE LOW HANGING OUT ALONG THE
CENTRAL B.C. COAST. THE LOW WILL MAINTAIN MODERATE S-SW FLOW ACROSS
THE AREA THROUGH THIS EVENING BEFORE DISSIPATING LATE TONIGHT...SO
THE SCA WILL REMAIN IN EFFECT THROUGH THIS EVENING.

GFS/ECMWF ARE IN DECENT AGREEMENT FOR WEDNESDAY WITH A WEAK SURFACE
RIDGE BUILDING BRIEFLY OVER THE AREA. WINDS ARE STILL EXPECTED TO
DROP BELOW SCA LEVELS. THE DECENT AGREEMENT EXTENDS TO THE NEXT
FRONTAL SYSTEM LATE WEDNESDAY NIGHT AND THURSDAY. AN APPROACHING
UPPER LEVEL SHORTWAVE TROUGH WILL STIMULATE A WAVE OFFSHORE ON THE
OLD BAROCLINIC ZONE LEFTOVER FROM THIS MORNINGS FRONT. THE RESULTING
LOW OR SURFACE TROUGH WILL HEAD N OFFSHORE TOWARD THE CENTRAL B.C.
COAST. THE MAINLY EASTERLY PRESSURE GRADIENTS WILL PROBABLY GENERATE
SUB-GALE WINDS OVER THE AREA. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...

WA...WIND ADVISORY NORTHWEST INTERIOR THIS MORNING.
PZ...GALE WARNING COASTAL WATERS...ENTRANCES TO THE STRAIT...
     ADMIRALTY INLET...NORTHERN INLAND WATERS.
     SMALL CRAFT ADVISORY ABOVE AREAS LATER THIS MORNING.
     SMALL CRAFT ADVISORY PUGET SOUND...CENTRAL STRAIT.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.

&&

$$

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










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