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000
FXUS66 KSEW 120958
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 AM PDT SUN MAY 12 2013

.SYNOPSIS...A FRONT WILL SPREAD AREAS OF RAIN INTO WESTERN
WASHINGTON TODAY. ANOTHER WEATHER SYSTEM WILL REACH THE AREA MONDAY
WITH RAIN AND ISOLATED THUNDERSTORMS. COOL AND UNSETTLED CONDITIONS
WILL PERSIST INTO NEXT WEEKEND.

&&

.SHORT TERM...A FRONTAL SYSTEM OVER THE OFFSHORE WATERS WILL MOVE
ONSHORE ACROSS WESTERN WASHINGTON TODAY SPREADING LIGHT RAIN ACROSS
THE AREA. THE BULK OF THE PRECIPITATION IS EXPECTED TO FALL ALONG
THE COAST AND THE NORTHERN PART OF THE FORECAST AREA...BUT MOST
PLACES SHOULD SEE SOME PRECIPITATION BY LATE THIS MORNING.
ALONG WITH THE CLOUDS AND PRECIP WILL BE COOLER TEMPERATURES...MUCH
CLOSER TO CLIMATOLOGICAL NORMS. PRECIP WILL DISSIPATE THIS EVENING
AS THE FRONT MOVES EAST OF THE AREA. A SECONDARY SYSTEM WILL SPREAD
MORE PRECIPITATION INTO WESTERN WASHINGTON MONDAY MORNING. THE
MODELS CONTINUE TO INDICATE THAT THE UPPER LEVEL TROUGH ASSOCIATED
WITH IT WILL BECOME NEGATIVELY TILTED WITH SOME MODEST INSTABILITY.
A CHANCE OF THUNDERSTORMS WAS ADDED TO THE FORECAST FOR MONDAY BY
THE PREVIOUS SHIFT. TEMPERATURES WILL COOL FURTHER ON MONDAY...WITH
MOST PLACES BELOW NORMAL FOR THE FIRST TIME IN 10+ DAYS. FAIRLY
STRONG PRESSURE RISES BEHIND MONDAYS FRONT WILL PRODUCE BREEZY TO
LOCALLY WINDY CONDITIONS DURING THE AFTERNOON AND EVENING. SHOWERS
WILL LINGER INTO THE EVENING AS THE TROUGH LIFTS OUT OF THE AREA.
UPPER HEIGHTS RECOVER SOMEWHAT ON TUESDAY...BUT ONSHORE FLOW
PERSISTS FOR A CHANCE OF SHOWERS AND COOL TEMPERATURES.

.LONG TERM...BOTH THE EURO AND GFS BRING ANOTHER TROUGH ONSHORE LATE
WEDNESDAY. IT APPEARS TO BE A WEAK SYSTEM WITH MOST OF THE PRECIP
DESTINED FOR BRITISH COLUMBIA AND COASTAL AREAS OF WESTERN
WASHINGTON. A SERIES OF WEAK SYSTEMS WILL AFFECT THE REGION INTO
NEXT WEEKEND...BUT THE TIMING HAS VARIED FROM RUN TO RUN AND MODEL
TO MODEL. ALL IN ALL...IT WILL BE AN UNSETTLED PERIOD WITH A CHANCE
OF SHOWERS AT TIMES AND TEMPERATURES RUNNING BELOW NORMAL.  27

&&

.AVIATION...MODERATE SW FLOW ALOFT TODAY THROUGH TONIGHT WITH UPPER
RIDGING OVER THE ROCKIES AND AN UPPER TROUGH APPROACHING THE AREA
FROM THE WEST. THE AIR MASS WILL BE GENERALLY MOIST AND STABLE
THROUGH TONIGHT.

RADAR AND SATELLITE IMAGERY SHOW AN INCOMING FRONTAL SYSTEM SITTING
FROM CENTRAL VANCOUVER ISLAND SOUTHWARD TO 40N 131W. PRE FRONTAL
PRECIPITATION EXTENDS AS FAR EAST AS A BELLINGHAM TO HOQUIAM LINE AT
0915Z. THE PRECIPITATION AND FRONT WILL MOVE EAST...WITH THE FRONT
MOVING INTO THE WESTERN WASHINGTON INTERIOR ABOUT 18Z TODAY. THE
FRONT WILL BE GRADUALLY WEAKENING AS IT MOVES EAST...AND IS EXPECTED
TO GRADUALLY DISSIPATE AS IT MOVES INTO THE CASCADES THIS AFTERNOON.

CEILINGS AND VISIBILITIES WILL RAPIDLY DEGRADE AS PRECIPITATION
BEGINS AHEAD OF THE FRONT. BY 14Z EXPECT GENERALLY MVFR CEILINGS AND
VISIBILITIES ACROSS THE INTERIOR AND IFR CONDITIONS ALONG THE COAST.
CONDITIONS WILL SLOWLY IMPROVE AFTER 19Z AS THE FRONT WEAKENS AND
MOVES EAST.

VFR TO MVFR CEILINGS ARE EXPECTED LATE THIS AFTERNOON THROUGH
TONIGHT AS WEAK RIDGING MOVES ACROSS THE AREA BETWEEN TODAYS FRONT
AND A STRONG TROUGH THAT WILL BE APPROACHING THE AREA MONDAY
AFTERNOON. ALBRECHT

KSEA...EXPECT CONDITIONS TO DEGRADE TO 4-6SM -RA BR SCT-BKN020
BKN-OVC035 BY 12Z. COLD FRONTAL PASSAGE IS EXPECTED AROUND 18Z WITH
P6SM SCT025 BKN035 BEHIND THE FRONT. SHOWERS WILL DIMINISH AFTER
23Z. WIND S/SW WIND 5-8 KT RISING TO 9-14 KT 14Z-18Z SUNDAY THEN
DIMINISHING TO S 5-9 KT AFTER 02Z. ALBRECHT

&&

.MARINE...A COLD FRONT EXTENDS FROM CENTRAL VANCOUVER ISLAND SOUTH
TO 40N 131W EARLY THIS MORNING. THE FRONT WILL SLOWLY WEAKEN AS IT
MOVES INTO THE INLAND WATERS MIDDAY TODAY...THEN WILL DISSIPATE AS
IT MOVES INTO THE CASCADES THIS AFTERNOON AND TONIGHT. MARGINAL
SMALL CRAFT ADVISORY CONDITIONS ARE EXPECTED AHEAD AND WITH THE
FRONT ALONG THE COAST -EXCEPT FOR THE AREA NEAR GRAYS HARBOR...AND
TODAY FROM NORTHERN PUGET SOUND AND HOOD CANAL INTO ADMIRALTY INLET
AND PORTIONS OF THE NORTHERN INLAND WATERS. THE WINDS OVER THE
INLAND WATERS WILL BE CAUSED BY A COMBINATION OF THE WEAKENING FRONT
AND FLOW ALOFT INTERACTING WITH THE TERRAIN.

WEAKER SOUTHERLY FLOW IS EXPECTED TONIGHT THROUGH THE FIRST PART OF
MONDAY. THEN...A STRONG SURFACE TROUGH WILL SWEEP ACROSS THE WATERS
MONDAY AFTERNOON AND EVENING. THIS FEATURE COULD BE ACCOMPANIED BY
ISOLATED THUNDERSTORMS MONDAY AFTERNOON...AND WILL BE FOLLOWED BY A
STRONG PUSH OF SW-W GRADIENTS LATE MONDAY AFTERNOON AND MONDAY
NIGHT. AT THIS TIME RATHER WIDESPREAD SMALL CRAFT ADVISORY SW-W
WINDS ARE EXPECTED ACROSS MOST WATERS LATER MONDAY INTO MONDAY
NIGHT.

HIGH PRES WILL BUILD BACK INTO THE WATERS ON TUESDAY. A WEAKER
FRONTAL SYSTEM IS EXPECTED TO MOVE INTO THE COASTAL WATERS GIVING
POSSIBLE  SMALL CRAFT ADVISORY CONDITIONS THERE TUESDAY NIGHT INTO
WEDNESDAY. ALBRECHT

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY ALL COASTAL ZONES EXCEPT POINT
     GRENVILLE TO CAPE SHOALWATER.
     SMALL CRAFT ADVISORY PUGET SOUND AND HOOD CANAL...ADMIRALTY
     INLET...AND THE NORTHERN INLAND WATERS THROUGH 8 AM THROUGH
     3 PM TODAY.

&&

$$

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