Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 181045 CCA
AFDSEW

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE SEATTLE WA
330 AM PDT FRI JUL 18 2014

CORRECTED WORDING IN THE SYNOPSIS

.SYNOPSIS...MODERATE ONSHORE FLOW THIS MORNING WILL BRING AREAS OF
LOW STRATUS TO WESTERN WASHINGTON. THIS AFTERNOON WILL BE PARTLY
SUNNY AS HIGH CLOUDS FROM AN APPROACHING UPPER LEVEL LOW SPREAD
INLAND. THE UPPER LEVEL LOW WILL BRING SCATTERED SHOWERS TO THE AREA
FRIDAY NIGHT...WITH SHOWERS INCREASING SATURDAY AFTERNOON AND
EVENING AS THE LOW NEARS THE WASHINGTON COAST. A BROAD UPPER LEVEL
TROUGH WILL REMAIN OVER THE REGION THROUGH MID NEXT WEEK FOR MOSTLY
CLOUDY SKIES AND SCATTERED SHOWERS. ANOTHER UPPER LEVEL LOW PRESSURE
SYSTEM MAY IMPACT THE AREA TUESDAY NIGHT INTO WEDNESDAY.

&&

.SHORT TERM...ON SATELLITE IMAGERY THE MARINE PUSH OF LOW STRATUS IS
LOOKING SLIGHTLY WEAKER THIS MORNING THAN YESTERDAY MORNING...AND
WILL LIKELY NOT MAKE IT INTO THE NORTH INTERIOR. PORTIONS OF THE
EAST PUGET SOUND LOWLANDS MAY ALSO REMAIN SUNNY THIS MORNING AS THE
LOW STRATUS DO NOT HAVE AS MUCH OF AN EASTWARD EXTENT. PRES
GRADIENTS ARE ALSO WEAKER THAN THEY WERE YESTERDAY MORNING...FURTHER
SLOWING THE MARINE PUSH.

HIGH CLOUDS WILL NUDGE THEIR WAY INTO THE AREA LATER TODAY AND INTO
TONIGHT AS A WEAK SHORTWAVE TROUGH MOVES OVER BRITISH COLUMBIA.
EXPECT SHOWERS TO DEVELOP OVERNIGHT. A SLIGHTLY STRONGER SHORTWAVE
TROUGH ASSOCIATED WITH AN UPPER LEVEL LOW WILL IMPACT THE AREA ON
SATURDAY...BRINGING MORE WIDESPREAD SHOWERS. TEMPERATURES WILL
CONTINUE TO SLOWLY DROP THROUGH SUNDAY...WHEN INTERIOR HIGHS MAY
BARELY BREAK 70...MUCH COOLER THAN WE HAVE BEEN EXPERIENCING.

ON SUNDAY ANOTHER VERY WEAK TROUGH WILL IMPACT THE AREA...KEEPING
SHOWERS IN THE FORECAST. SHOWERS WILL BECOME MORE ISOLATED AFTER
SUNDAY NIGHT.

.LONG TERM...AN UPPER LEVEL LOW PRESSURE SYSTEM AND ITS ASSOCIATED
WEAK SURFACE LOW WILL IMPACT THE AREA TUESDAY NIGHT INTO WEDNESDAY.
IF THE SYSTEM COMES ASHORE TO THE NORTH OVER NORTHERN VANCOUVER
ISLAND...AS THE ECMWF FORECASTS...THERE WILL NOT BE MUCH OF AN
IMPACT...PERHAPS A FEW ISOLATED SHOWERS. HOWEVER...IF THE GFS40 IS
CORRECT AND THE SYSTEM MOVES DIRECTLY OVER WESTERN WASHINGTON...WE
WILL SEE MORE WIDESPREAD PRECIPITATION AND HIGHER AMOUNTS. BEHIND
THE SYSTEM...MODELS HINT AT A RIDGE BUILDING IN BRINGING FAIR
WEATHER...HOWEVER UNCERTAINTY AT THIS POINT IS FAIRLY HIGH.

&&

.AVIATION....LIGHT NW FLOW ALOFT TODAY AHEAD OF A TROUGH. THE FLOW
WILL BECOME MODERATE W-NWLY TONIGHT AND SATURDAY AS THE TROUGH MOVES
OVER THE REGION. STABLE ATMOSPHERE. MOIST IN THE LOWER LEVELS
TODAY...THEN MOISTURE INCREASING AT ALL LEVELS TONIGHT AND SATURDAY.
EXPECT RAIN AT TIMES FROM KPAE NWD LATER TONIGHT AND SATURDAY WITH
SPRINKLES OR LIGHT RAIN ACROSS THE REMAINDER OF THE AREA.

SATELLITE IMAGERY INDICATES STRATUS IS A BIT MORE SPARSE THAN
PREVIOUS MORNINGS. LOW CLOUDS ARE SO FAR CONFINED TO THE WRN
PORTION OF THE SW INTERIOR...LOWER CHEHALIS GAP...AND SPILLING INTO
THE SW PORTION OF PUGET SOUND. A MIX OF IFR AND LOW MVFR STRATUS IS
EXPECTED TO FILL IN FURTHER...ESPECIALLY AROUND THE PUGET SOUND
REGION AFFECTING THE KSEA/BFI/KOLM TERMINALS...AND POSSIBLY KPAE.
THE LOW CLOUDS SHOULD SCATTER OUT BY LATE MORNING MOST PLACES.

KSEA...SOUTH TO SOUTHWEST WIND 5-10 KT. STRATUS OVER WRN PORTIONS OF
THE SOUND IS EXPANDING EWD. LOW CLOUDS SHOULD REACH KSEA BY 12Z.
CIGS MOST LIKELY IN THE 700-900 FT...THEN SCATTERING BY ROUGHLY 17Z.

&&

.MARINE...ONSHORE FLOW WILL CONTINUE TODAY AND INCREASE THIS EVENING
AS A TROUGH APPROACHES. THE FLOW THROUGH THE STRAIT WILL BE MARGINAL
FOR GALES AND CONFIDENCE IS LOW. WILL LEAVE THE GALE WATCH IN EFFECT
FOR THIS EVENING.

A SERIES OF WEAK UPPER TROUGHS WILL MOVE THROUGH THE REGION THROUGH
TUESDAY. ONSHORE FLOW WILL PERSIST AS HIGH SURFACE PRESSURE REMAINS
OFFSHORE WITH LOWER PRESSURE INLAND.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY COASTAL WATERS THROUGH NOON.
     SMALL CRAFT ADVISORY CENTRAL AND E STRAIT THROUGH 7 AM PDT.
     GALE WATCH CENTRAL STRAIT OF JUAN DE FUCA AND EAST STRAIT
     TONIGHT.

&&

$$

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










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