Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 091554
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT TUE SEP 9 2014

.SYNOPSIS...AN UPPER TROUGH AND LOW LEVEL ONSHORE FLOW WILL RESULT
IN MOSTLY CLOUDY AND COOL WEATHER TODAY. AN UPPER RIDGE WILL BUILD
MID WEEK AND PERSIST THROUGH THE WEEKEND. LOW LEVEL OFFSHORE FLOW
WILL ALLOW FOR GRADUALLY WARMING TEMPERATURES EACH DAY...WITH HIGHS
REACHING THE LOWER TO MID 80S BY THE WEEKEND.

&&

.SHORT TERM...LIGHT SHOWERS ARE LINGERING IN PUGET SOUND THIS
MORNING FROM A WEAK PUGET SOUND CONVERGENCE ZONE. THESE SHOWERS WILL
DIMINISH LATE THIS MORNING. THE SYNOPTIC PATTERN IS DOMINATED BY A
HIGH AMPLITUDE RIDGE OFFSHORE ALONG 140W...WITH NORTHERLY FLOW ALOFT
OVER WESTERN WA. A WEAK UPPER LEVEL DISTURBANCE MAY TRIGGER ISOLATED
SHOWERS IN THE NORTH CASCADES THIS AFTERNOON...OTHERWISE THE REST OF
THE CWA WILL BE DRY. TEMPS WILL REMAIN A FEW DEGREES BELOW NORMAL
TODAY WITH HIGHS IN THE MID 60S TO LOWER 70S. SKIES ARE MOSTLY
CLOUDY IN THE INTERIOR BUT WE MAY SEE SOME CLEARING IN THE
AFTERNOON. EXPECT PATCHY FOG OVERNIGHT WITH LOW IN THE LOWER TO MID
50S.

MODELS SHOW WESTERN WA DRYING OUT ON WED AS THE UPPER LEVEL RIDGE
NUDGES INLAND AND LOW LEVEL OFFSHORE FLOW INCREASES. THERE IS A
PRETTY GOOD NORTHERLY PRES GRADIENT WITH THE THERMAL TROUGH ALONG
THE COAST AND SURFACE HIGH PRES EXTENDING FROM B.C. TO ALBERTA.
KOLM-KBLI IS -5 MB AND WE SHOULD SEE NORTH WINDS OF AT LEAST 10 TO
20 MPH THROUGH THE INTERIOR. THIS WILL HELP SCOUR OUT THE REGION
KEEPING SKIES CLEAR.

HIGH PRES WILL REMAIN OVER THE PAC NW THU AND FRI FOR MORE DRY AND
STABLE WEATHER ACROSS WESTERN WA. THE THERMAL TROUGH WILL REMAIN
ALONG THE COAST FOR OFFSHORE WINDS. TEMPS WILL MODERATE AND WE
SHOULD SEE HIGHS IN THE 70S TO LOWER 80S...INCLUDING THE COAST. 33

.LONG TERM...PREVIOUS DISCUSSION...THE THEME FOR THE EXTENDED IS DRY
AND WARMER. BOTH THE GFS/ECMWF AGREE THAT A STRONG RIDGE OF HIGH
PRESSURE OVER THE ERN PAC WILL BUILD INTO THE PAC NW. 500 MB HEIGHTS
GRADUALLY RISE WITH LIGHT OR OFFSHORE FLOW. HIGHS IN THE MID TO
UPPER 70S LATE IN THE WEEK SHOULD REACH THE LOW TO MID 80S BY THE
WEEKEND. SOME MODELS SHOW THE RIDGE SHIFTING INLAND EARLY NEXT WEEK
AS A WEAK UPPER LEVEL SYSTEM LIFTS ACROSS. THIS SCENARIO WOULD
LIKELY INDUCE A MARINE PUSH WITH MODERATING TEMPERATURES AND SOME
INCREASED CLOUDS. NOT ALL MODELS SHOW THIS SO THE FORECAST HIGH
TEMPERATURES ARE ONLY TRENDED DOWN SLIGHTLY.  MERCER

&&

.AVIATION...FLOW ALOFT WILL REMAIN NORTHWESTERLY THROUGH WEDNESDAY.
LOW LEVEL ONSHORE FLOW WILL PERSIST THROUGH THIS AFTERNOON THEN
BECOME MORE NORTHERLY AND OFFSHORE WEDNESDAY. THE AIR MASS IS MOIST
AND STABLE THIS MORNING THOUGH CONSIDERABLE CLEARING IS APPARENT
OVER SOME AREAS.

STRATUS WITH CEILINGS AROUND 2K FT ARE OVER PUGET SOUND AND ADJACENT
LAND AREAS. CEILINGS WILL LIFT AND DISSIPATE TODAY WITH SCATTERING
OUT LIKELY DURING THE AFTERNOON. SOME STRATUS WILL RETURN OVERNIGHT
BUT AREAL EXTENT WILL BE LESS THAN TODAY AND CLOUDS WILL EVAPORATE
MORE RAPIDLY WEDNESDAY MORNING.

KSEA...MVFR CEILINGS WILL LINGER THROUGH THE MORNING...LIFTING AND
SCATTERING OUT DURING THE AFTERNOON. WINDS WILL REMAIN SOUTHWESTERLY
4 TO 8 KTS. CHB

&&

.MARINE...SURFACE HIGH PRESSURE OVER THE NORTHEAST PACIFIC WILL KEEP
THE FLOW ONSHORE THROUGH THIS AFTERNOON. GRADIENTS WILL REMAIN
STRONG ENOUGH TO SUPPORT ANOTHER ROUND OF SMALL CRAFT ADVISORY
WESTERLIES IN THE CENTRAL AND EASTERN STRAIT TONIGHT.

GRADIENTS AND FLOW WILL BECOME OFFSHORE AND NORTHERLY WEDNESDAY AS A
SURFACE HIGH DROPS SOUTH ACROSS ALBERTA AND A THERMALLY INDUCED
SURFACE TROUGH WORKS NORTH ALONG THE WASHINGTON COAST. THIS PATTERN
WILL PRODUCE STRONGER NORTHEASTERLY TO NORTHERLY WINDS OVER SOME OF
THE INTERIOR WATERS WEDNESDAY AND WEDNESDAY EVENING...POTENTIALLY
REACHING SMALL CRAFT ADVISORY LEVELS. RISING EASTERLY WINDS MAY ALSO
REACH SMALL CRAFT ADVISORY LEVELS THROUGH THE WEST ENTRANCE OF THE
STRAIT OF JUAN DE FUCA WEDNESDAY NIGHT AND THURSDAY MORNING. THE
OFFSHORE FLOW PATTERN WILL CONTINUE THROUGH SATURDAY. CHB

&&

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


&&

$$

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