Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 040337
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
845 PM PDT TUE MAY 3 2016

.SYNOPSIS...A TROUGH OFF THE PACIFIC NORTHWEST COAST WILL MAINTAIN
COOLER ONSHORE FLOW AND SOMEWHAT UNSETTLED CONDITIONS OVER THE AREA
THROUGH THURSDAY. HIGH PRESSURE WILL BUILD OVER THE REGION FRIDAY
AND SATURDAY BRINGING DRY AND WARM WEATHER. AN UPPER TROUGH WILL
BRUSH WESTERN WASHINGTON SUNDAY WITH A RETURN TO COOLER ONSHORE FLOW.

&&

.SHORT TERM...RADAR SHOWS SCATTERED SHOWERS OVER THE CASCADES AND
ISOLATED SHOWERS ELSEWHERE. THERE HAVE BEEN ISOLATED LIGHTNING
STRIKES NEAR THE CASCADE CREST. THE SHOWERS ARE LIKELY TO CONTINUE
OVERNIGHT THOUGH THE THUNDERSTORMS ARE PERHAPS DONE.

A FRONTAL BAND WILL REMAIN STALLED ACROSS WESTERN WASHINGTON
WEDNESDAY. WITH MOISTURE OVER THE AREA IT WILL STAY MOSTLY CLOUDY
WITH SPOTTY SHOWERS. A STRONGER ONSHORE PUSH MAY ALSO RESULT IN
AREAS OF MORNING STRATUS WITH LOWER HIGH...CLOSER TO AVERAGE IN THE
LOW 60S.

MODELS ARE A BIT FASTER SHIFTING THE UPPER TROUGH AXIS THROUGH THE
AREA ON THURSDAY. BUT THERE IS STILL SOME TIMING UNCERTAINTY WITH A
CHANCE OF SHOWERS UNTIL THE AXIS SHIFTS EAST. AREAS WEST OF PUGET
SOUND WILL STAY MOSTLY DRY WITH PARTIAL SUNSHINE. EXPECT MORE CLOUDS
AND A CHANCE OF LINGERING SHOWERS EAST OF PUGET SOUND.

WESTERN WASHINGTON SHOULD GENERALLY CLEAR OUT THURSDAY NIGHT AS LOW
LEVEL NORTHERLY FLOW DEVELOPS UNDER A BUILDING UPPER HIGH. MODELS
STILL SHOW A SKINNY RIDGE NOSING NE OVER THE REGION FRIDAY WITH 500
MB HEIGHTS OVER 5700M. HIGH TEMPERATURES SHOULD RISE ABOVE AVERAGE
WITH LOW 70S AROUND THE INTERIOR LOWLANDS...ROUGHLY 10 DEGREES ABOVE
AVERAGE FOR THIS TIME OF YEAR. MERCER/BURKE

.LONG TERM...PREVIOUS DISCUSSION...UPPER LEVEL HIGH PRESSURE WILL
PERSIST OVER THE PAC NW THROUGH SATURDAY. IT SHOULD REMAIN DRY WITH
LIGHT WLY ONSHORE GRADIENTS DURING THE AFTERNOON. THIS WILL INHIBIT
HIGH TEMPERATURES ALONG THE COAST BUT IT SHOULD BE A FEW DEGREES
WARMER OVER THE INTERIOR.

THE GFS/ECMWF/CANADIAN ARE IN BETTER AGREEMENT TODAY IN SHOWING A
TROUGH CROSSING B.C. AND BRUSHING WRN WA ON SUNDAY. THIS SYSTEM
SHOULD INDUCE STRONGER ONSHORE FLOW AND DEEPEN THE MARINE LAYER.
HIGHS SHOULD DROP BACK DOWN INTO THE LOW 60S IN THIS PATTERN WITH
AREAS OF MORNING CLOUDS AND ONLY PARTIAL AFTERNOON SUN. THE 12Z
GFS/ECMWF BOTH SHOW SOME SPOTTY LIGHT QPF MOST LIKELY FALLING AS
SOME DRIZZLE FROM THE MARINE LAYER. THIS IS DIFFERENT THAN PREVIOUS
DRY MODEL RUNS AND ANY DRIZZLE COULD VERY WELL NOT EVEN MEASURE.
HAVE LEFT OUT ANY MENTION OF PRECIPITATION FOR NOW.

COOL ONSHORE FLOW MAY CONTINUE INTO MONDAY BUT THERE SHOULD BE A BIT
MORE AFTERNOON SUNSHINE AS THE TROUGH MOVES EAST. THE GFS/ECMWF
BOTH BUILD A RIDGE TUESDAY GIVING DRY AND WARMER WEATHER. MERCER

&&

.AVIATION...SOUTHERLY FLOW CONTINUES ALOFT OVER WESTERN
WASHINGTON THIS EVENING...AHEAD OF AN OFFSHORE UPPER TROUGH
SLOWLY APPROACHING THE PACIFIC NORTHWEST. THE AIR MASS IS WEAKLY
UNSTABLE -- MAINLY OVER THE MOUNTAINS -- WITH INCREASING MOISTURE
ALOFT. THE UPPER PATTERN WILL CHANGE LITTLE THROUGH WEDNESDAY.
THERE WILL BE SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS MAINLY
ALONG THE CASCADES CREST.

IN ADDITION LOW LEVEL ONSHORE FLOW IS INCREASING...WHICH WILL
CAUSE LOW LEVEL MOISTURE TO INCREASE OVERNIGHT. WIDESPREAD MVFR
AND LOCAL IFR CONDITIONS ARE LIKELY LATE TONIGHT AND WEDNESDAY
MORNING.

KSEA...WEST TO SOUTHWEST WIND 3-8 KT TRENDING TO NORTHERLY LATER
THIS EVENING. KSEA WILL PROBABLY HAVE CEILINGS AROUND 1500 FT --
AT LEAST AT TIMES -- BETWEEN ROUGHLY 5 AM AND NOON WEDNESDAY. MCDONNAL

&&

.MARINE...ONSHORE FLOW IS INCREASING THIS EVENING. GALE WESTERLIES
WERE DEVELOPING IN THE CENTRAL STRAIT OF JUAN DE FUCA AND EAST
ENTRANCE STRAIT AT 8 PM...AND THE GALE WARNING REMAINS IN EFFECT. SMALL
CRAFT ADVISORY WINDS ALL OTHER MARINE ZONES EXCEPT PUGET SOUND AND
HOOD CANAL. NORTHWEST FLOW WILL PERSIST INTO NEXT WEEKEND BETWEEN
HIGH PRESSURE OFFSHORE AND LOW PRESSURE INLAND. MCDONNAL

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 6 AM PDT THURSDAY FOR 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.

     GALE WARNING UNTIL 3 AM PDT WEDNESDAY FOR CENTRAL U.S. WATERS
     STRAIT OF JUAN DE FUCA-EAST ENTRANCE U.S. WATERS STRAIT OF
     JUAN DE FUCA.

     SMALL CRAFT ADVISORY UNTIL 6 AM PDT WEDNESDAY FOR ADMIRALTY
     INLET-NORTHERN INLAND WATERS INCLUDING THE SAN JUAN ISLANDS-
     WEST ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA.

&&

$$

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