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000
FXUS66 KSEW 172202
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PDT FRI MAY 17 2013

.SYNOPSIS...AN UPPER TROUGH WILL ARRIVE MOVE INLAND SATURDAY GIVING
A COOL SHOWERY DAY. AN UPPER RIDGE WILL BUILD OFFSHORE SUNDAY AND
MOVE INLAND MONDAY FOR WARMER AND MOSTLY DRY WEATHER. A DEEP UPPER
LOW WILL REACH THE AREA TUESDAY AND LINGER THROUGH MIDWEEK FOR
SHOWERY AND UNSEASONABLY COOL WEATHER. SOME IMPROVEMENT IS POSSIBLE
BY MEMORIAL DAY WEEKEND.

&&

.SHORT TERM...CLOUDS PERSISTED LONGER OVER INLAND AREAS TODAY AS A
RAIN BAND SLOWLY MOVED NORTH. MEANWHILE WHAT WAS SUPPOSED TO BE AN
AREA OF PARTIAL CLEARING TO THE WEST QUICKLY FILLED IN WITH CUMULUS
AND SCATTERED SHOWERS. HIGH TEMPERATURES WILL TOP OUT IN THE LOW
60S...UPPER 50S NORTH. THERE WILL LIKELY BE SOME BREAKS IN THE
CLOUDS TONIGHT THAT ALLOW TEMPERATURES TO FALL TO NEAR 50 DEGREES.

A SIGNIFICANT UPPER TROUGH WILL MOVE ONTO THE COAST SATURDAY MORNING
THEN INLAND SATURDAY AFTERNOON. SHOWERS SHOULD BE MORE NUMEROUS WITH
THIS UPPER TROUGH...ESPECIALLY DURING THE 18Z-03Z PERIOD. THE CLOUDS
AND SHOWERS WILL DAMPEN TEMPERATURES FURTHER WITH HIGHS LUCKY TO
MAKE IT TO 60 DEGREES...AND PLENTY OF HIGHS IN THE 50S ARE LIKELY ON
THE COAST AND OVER THE NORTH.

AN UPPER RIDGE OF HIGH PRESSURE WILL BUILD OFF THE COAST SATURDAY
NIGHT AND SUNDAY. CONDITIONS SHOULD DRY AND THERE SHOULD BE AT LEAST
SOME CLEARING SUNDAY AFTERNOON...WITH HIGHS IN THE LOW TO MID 60S
OVER INLAND AREAS. DRY WEATHER IS LIKELY TO CONTINUE INTO MONDAY BUT
BY MONDAY AFTERNOON A DEEP UPPER TROUGH APPROACHING FROM THE
NORTHWEST WILL BEGIN TO AFFECT THE WEATHER. HAVE PUT A CHANCE OF
SHOWERS ON THE COAST AND OVER THE NORTH MONDAY AFTERNOON. CLOUDS
WILL BE INCREASING AND TEMPERATURES WILL BE NOTICEABLY LOWER IN THE
NORTH. SOUTHERN INLAND AREAS WILL PROBABLY HAVE LOTS OF HIGHS IN THE
60S AS THE CLOUDS WILL REACH THERE LAST. BURKE

.LONG TERM...THE UPEPR LOW DEEPENS AND MOVES TO JUST OFF THE COAST
ON TUESDAY. THE GFS AND EURO AGREE ON THIS. THEN BOTH MODELS MOVE
THE UPPER LOW INLAND AND KEEP IT MORE OR LESS OVER THE AREA
WEDNESDAY AND THURSDAY...ALTHOUGH BY THURSDAY THE TRACKS ARE
DIVERGING SIGNIFICANTLY. THE GFS MOVES THE LOW NORTH AND THE EURO
MOVES IT SOUTH...THEREBY MAKING FRIDAY A DRIER AND WARMER DAY
COMPLETELY BY COINCIDENCE.

IF THE MODELS ARE RIGHT...TUESDAY THROUGH THURSDAY ARE GOING TO BE
COOL AND SHOWERY DAYS. HIGHS MAY NOT GET OUT OF THE 50S. THERE COULD
BE SNOW SHOWERS IN THE MOUNTAINS WITH THE SNOW LEVEL DIPPING TO 3000
FEET OR SO. CONFIDENCE IS NOT PARTICULARLY HIGH IN ANY DETAILS. FOR
INSTANCE...THE ENSEMBLE GFS SOLUTIONS SHOW KSEA HIGHS ON TUESDAY
RANGING FROM 55 TO 68. HOWEVER IT SEEMS LIKELY THERE WILL BE SOME
VERY COOL DAYS WITH SHOWERS...PROBABLY MIXED IN WITH SOME PARTLY
SUNNY DAYS. BURKE

&&

.AVIATION...A WEAK TROUGH WAS GIVING SCATTERED SHOWERS ACROSS
WESTERN WA THIS AFTERNOON. A STRONGER FRONT WILL REACH WESTERN WA
SATURDAY AND A MORE ORGANIZED BAND OF PRECIP SHOULD MOVE THROUGH
WESTERN WA OVER THE COURSE OF THE DAY. THE AIR WILL REMAIN MOIST AND
SLIGHTLY UNSTABLE. LIGHT SW FLOW ALOFT.

KSEA...SCATTERED SHOWERS AND SLY BREEZE TONIGHT...MORE PRECIP ON
SATURDAY WITH THE NEXT FRONT.

&&

.MARINE...ONSHORE FLOW WILL CONTINUE. A WEAK SURFACE TROUGH
DISSIPATED OVER WESTERN WA TODAY. A FRONT JUST OUTSIDE OF 130W THIS
AFTERNOON WILL MOVE OVER WESTERN WA SATURDAY...THE WIND OVER THE
COASTAL WATERS SATURDAY MORNING SHOULD BE SOUTH OR SE AROUND 20KT.
BEHIND THE FRONT WLY FLOW WILL CONTINUE SAT NITE THROUGH SUNDAY
NIGHT...WITH SMALL CRAFT ADVISORY LEVEL WLY WINDS LIKELY IN THE
STRAIT IN THE EVENINGS. ANOTHER WEATHER SYSTEM WILL REACH THE AREA
MON NIGHT OR TUE.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&

$$

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