Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 230352
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 PM PDT FRI MAY 22 2015

.SYNOPSIS...HIGH PRESSURE OFFSHORE WILL MAINTAIN MODERATE TO STRONG
LOW LEVEL ONSHORE FLOW OVER WESTERN WASHINGTON THROUGH MID NEXT
WEEK. WEAK LOW PRESSURE WILL BRING A CHANCE OF SHOWERS MAINLY OVER
THE MOUNTAINS DURING THE AFTERNOON AND EVENINGS EACH DAY.

&&

.SHORT TERM...SHOWERS ARE WINDING DOWN ACROSS WESTERN WA THIS
EVENING AND MOSTLY LIMITED TO THE SW INTERIOR AND LOWER CHEHALIS
VALLEY. POPS AND WEATHER WERE UPDATED IN THE FORECAST ZONES BASED ON
THE LATEST TRENDS. LOW LEVEL ONSHORE FLOW WILL CONTINUE OVERNIGHT
FOR MOSTLY CLOUDY SKIES AND PATCHY DRIZZLE.

UPPER LEVEL RIDGING WILL CONTINUE TO DOMINATE ACROSS WESTERN CANADA
ON SATURDAY WHILE WEAK LOW PRES FORMS OVER S/SE B.C. NEAR HAIDA
GWAII. THERE IS ENOUGH LIFT AND INSTABILITY FOR A CHANCE OF SHOWERS
AND THUNDERSTORMS IN THE CASCADES ONCE AGAIN. THE LOWLANDS WILL BE
DRY ALTHOUGH STILL CLOUDY AND COOL UNDER THE STRATUS LAYER. EXPECT
HIGHS IN THE LOWER TO MID 60S SATURDAY AFTERNOON WHICH IS A FEW
DEGREES BELOW NORMAL. THE COAST WILL LIKELY REMAIN IN THE 50S.

THE UPPER LEVEL LOW WILL REMAIN OVER THE REGION SUNDAY AND MEMORIAL
DAY WITH SHOWERS AGAIN MAINLY FOCUSED IN THE CASCADES. LOW LEVEL
ONSHORE FLOW WILL PERSIST FOR MOSTLY CLOUDY SKIES ACROSS THE
LOWLANDS. 33

.LONG TERM...PREVIOUS DISCUSSION...GFS/ECMWF TAKE THE UPPER LEVEL
LOW E ON TUESDAY WITH N FLOW ALOFT DEVELOPING OVER W WA. THIS SHOULD
END ANY THREAT OF SHOWERS FOR THE LOWLANDS AND PROBABLY THE CASCADES
AS WELL. THE SURFACE RIDGE OVER THE NE PACIFIC WILL MAINTAIN THE
ONSHORE FLOW PATTERN NEXT WEEK FOR MOSTLY CLOUDY SKIES...BUT THE
FLOW COULD WEAKEN ENOUGH FOR A BIT MORE AFTERNOON SUNSHINE. KAM

&&

.AVIATION...LIGHT FLOW ALOFT WILL CONTINUE INTO SATURDAY. MODERATE
ONSHORE FLOW WILL EASE OVERNIGHT. THE AIR MASS IS MOIST AND SLIGHTLY
UNSTABLE. DEEP MARINE LAYER OVER WESTERN WASHINGTON WILL KEEP
CEILINGS FIRMLY MVFR TONIGHT AND SATURDAY MORNING.

KSEA...CEILINGS 2K FT THIS EVENING WILL REACH AS LOW AS 1K FT
OVERNIGHT. SOME IMPROVEMENT IS LIKELY SATURDAY AFTERNOON. SOUTHWEST
WIND 4-8 KT WILL CONTINUE TONIGHT AND SATURDAY. CHB

&&

.MARINE...HIGH PRES WILL REMAIN OFFSHORE WITH LOWER PRES INLAND.
ONSHORE FLOW OF VARYING STRENGTH WILL CONTINUE THROUGH WEDNESDAY.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY CENTRAL AND EAST STRAIT.

&&

$$

WWW.WEATHER.GOV/SEATTLE

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




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