Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 012149
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PDT FRI AUG 1 2014

.SYNOPSIS...AN UPPER LEVEL RIDGE WILL REMAIN OVER THE PACIFIC
NORTHWEST INTO NEXT WEEK. A SMALL WEAK UPPER LEVEL TROUGH WILL MOVE
UP OVER WESTERN WASHINGTON THIS EVENING FOR A CHANCE OF
THUNDERSTORMS. ONSHORE FLOW WILL BRING AREAS OF LATE NIGHT AND
MORNING CLOUDS WITH MOSTLY SUNNY AND WARM AFTERNOONS FROM SATURDAY
ONWARD.

&&

.SHORT TERM...THE THREAT FOR ISOLATED HIGH-BASED THUNDERSTORMS
CONTINUES ACROSS WESTERN WA LATE THIS AFTERNOON AND EVENING. POPS
ARE 20-30 PERCENT. THE MAIN FOCUS IS OVER THE INTERIOR /KING COUNTY
NORTHWARD/ AND ACROSS THE CASCADES. THE TRIGGER IS AN UPPER LEVEL
SHORT WAVE TROUGH WHICH IS RIDING N/NE ALONG THE WESTERN PERIPHERY
OF THE RIDGE. EXPECT LITTLE IF ANY PRECIP IN THE INTERIOR LOWLANDS.
THE FOCUS FOR THUNDERSTORMS WILL SWITCH TO THE CASCADES LATE TONIGHT
AS THE UPPER LEVEL DISTURBANCE EXITS.

MODELS SHOW ANOTHER WEAK DISTURBANCE CLIPPING THROUGH THE REGION ON
SAT FOR ANOTHER ROUND OF POSSIBLE THUNDERSTORMS...MAINLY IN THE
CASCADES. OTHERWISE EXPECT ANOTHER WARM DAY FOR THE INTERIOR WITH
HIGHS ONCE AGAIN IN THE LOWER TO MID 80S. LOW LEVEL ONSHORE FLOW
WILL BRING LOW CLOUDS AND COOLER WEATHER TO THE COAST. ONSHORE FLOW
WILL STRENGTHEN SAT NIGHT AND SUNDAY AND WILL LIKELY SEE MORE LOW
CLOUDS PUSHING INTO THE INTERIOR. THIS WILL HELP COOL TEMPS BACK
CLOSER TO NORMAL.

THE UPPER LEVEL RIDGE WILL REBUILD ON MONDAY WITH TEMPS RISING A FEW
DEGREES. NO OTHER SIGNIFICANT CHANGES BESIDES THAT. 33

.LONG TERM...THE UPPER LEVEL RIDGE OVER THE PAC NW IS SHOWING SIGNS
OF BREAKING DOWN AS WE HEAD INTO THE MIDDLE OF NEXT WEEK. BY THEN
THE RIDGE AXIS IS SHIFTING INTO THE CENTRAL U.S. WITH THE FLOW
TURNING MORE ZONAL OVER WA. THERE IS EVEN A WEAK FRONT CROSSING THE
REGION BUT IT LOOKS DRY IN THE MODELS. BUT THIS FRONT WILL INCREASE
LOW LEVEL ONSHORE FLOW FOR AN INCREASE IN LOW CLOUDS. A WEAK UPPER
LEVEL TROUGH WILL FORM OVER THE REGION LATE IN THE WEEK WITH TEMPS
DIPPING A FEW MORE DEGREES...BUT STILL NEAR NORMAL. 33

&&

.AVIATION...AN UPPER RIDGE CENTERED OVER THE INTERIOR WEST WILL KEEP
HEIGHTS HIGH AND UPPER FLOW SOUTHWESTERLY TONIGHT AND SATURDAY. AT
THE SURFACE THERE IS MODERATE ONSHORE FLOW. A LINE OF ACCAS WITH
ISOLATED THUNDERSTORMS...CURRENTLY OVER SOUTHERN KING COUNTY...WILL
MOVE NORTH THROUGH NORTHWESTERN WASHINGTON THROUGH ABOUT 02Z THIS
EVENING. OTHERWISE SKIES WILL BE MOSTLY CLEAR. STRATUS WILL RETURN
TO THE COAST OVERNIGHT BUT INLAND AREAS SHOULD HAVE MINIMAL STRATUS
SATURDAY. THERE IS A CHANCE OF THUNDERSTORMS IN THE CASCADES ON
SATURDAY.

ANY CEILINGS WILL BE VFR EXCEPT FOR THE IMMEDIATE COAST WHERE THERE
WILL LIKELY BE SOME IFR OVERNIGHT.

KSEA...MID AND HIGH CLOUDS WILL DIMINISH AFTER 00Z AND SKIES WILL BE
MOSTLY CLEAR TONIGHT. THE SLIGHT CHANCE OF A THUNDERSTORM WILL ALSO
GO AWAY AFTER 00Z OR SO. NOT EXPECTING ANY STRATUS SATURDAY MORNING.
WINDS WILL BE NORTHWEST 4-8 KT. CHB

&&

.MARINE...HIGH PRESSURE IS OVER THE OFFSHORE WATERS WITH THERMALLY
INDUCED LOW PRESSURE EAST OF THE CASCADES. ONSHORE GRADIENTS ARE
WEAKER THAN THIS TIME YESTERDAY SO HAVE FORECAST SLIGHTLY WEAKER
WINDS IN THE STRAIT THIS EVENING...20-30 KT.

ONSHORE GRADIENTS OF VARYING STRENGTH WILL PERSIST INTO NEXT WEEK.
SMALL CRAFT ADVISORY STRENGTH WINDS ARE POSSIBLE EACH AFTERNOON AND
EVENING IN THE STRAIT. CHB

&&

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

&&

$$

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





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