Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 181601
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT FRI JUL 18 2014

.SYNOPSIS...WESTERN WASHINGTON WILL BE PARTLY SUNNY AND SOMEWHAT
COOLER TODAY. AN UPPER TROUGH MOVING THROUGH BRITISH COLUMBIA WILL
BRING SHOWERS TO THE FORECAST AREA TONIGHT THROUGH SUNDAY NIGHT...
ESPECIALLY FOR THE COAST AND MOUNTAINS. SUNDAY WILL BE PARTLY SUNNY
WITH SPOTTY LIGHT SHOWERS. A BROAD UPPER TROUGH WILL REMAIN OVER THE
REGION MONDAY TO WEDNESDAY FOR MOSTLY CLOUDY SKIES AND SOME SHOWERS.

&&

.SHORT TERM...WE HAVE WESTERLY FLOW ALOFT OVER THE PACIFIC NORTHWEST
THIS MORNING...AHEAD OF A FLAT UPPER RIDGE CENTERED WELL OFFSHORE
OVER THE NORTHEAST PACIFIC OCEAN. HIGH CLOUDS AT THE LEADING EDGE OF
AN UPPER SHORTWAVE TROUGH MOVING OVER THE NORTH SIDE OF THE RIDGE
ARE JUST STARTING TO REACH WESTERN WASHINGTON. STRATUS THAT PUSHED
INLAND OVERNIGHT STILL COVERS MUCH OF THE WESTERN WASHINGTON
LOWLANDS AT 8 AM...ESPECIALLY WEST OF SEATTLE.

THE STRATUS OVER THE INTERIOR LOWLANDS SHOULD DISSIPATE BY NOON...
BUT MID AND HIGH CLOUDS WILL INCREASE AS THE UPPER TROUGH
APPROACHES. THE COAST IS LIKELY TO REMAIN GENERALLY CLOUDY. HIGH
TEMPERATURES TODAY WILL BE IN THE MID TO UPPER 60S AT THE COAST AND
70S TO LOWER 80S INLAND. SEATAC WILL PROBABLY FALL SHORT OF 80
DEGREES TODAY...WHICH WOULD BRING THE CURRENT STREAK OF 12
CONSECUTIVE 80+ DEGREE DAYS TO AN END. THAT STREAK IS TIED FOR THE
SECOND LONGEST IN THE HISTORY OF SEATAC...WHERE OBSERVATIONS STARTED
IN 1948.

THE UPPER SHORTWAVE WILL REACH THE COAST OF BRITISH COLUMBIA LATE
TONIGHT...MOVE THROUGH THE PROVINCE ON SATURDAY...AND THEN MAKE ITS
WAY EAST OF THE CANADIAN ROCKIES SATURDAY NIGHT. THIS FEATURE WILL
BRING SOME SHOWERS TO THE FORECAST AREA...ESPECIALLY THE COAST AND
MOUNTAINS ON SATURDAY AND SATURDAY NIGHT. PARTS OF THE NORTH
CASCADES WILL PROBABLY RECEIVE MORE THAN AN INCH OF PRECIPITATION
DURING THE 36-HOUR PERIOD ENDING LATE SATURDAY NIGHT...WITH CLOSE TO
AN INCH OVER THE OLYMPICS. THE SNOW LEVEL WILL BE 10000 TO 12000 FT.

SHOWERS WILL BE MORE LIMITED OVER THE INTERIOR LOWLANDS TONIGHT
THROUGH SATURDAY NIGHT. SEATTLE AND THE CENTRAL PUGET SOUND REGION
IN PARTICULAR WILL BE IN THE SHADOW OF THE OLYMPIC MOUNTAINS. IF
SEATAC DOES RECEIVE MEASURABLE RAINFALL...IT WILL BE THE FIRST SINCE
THERE JUNE 28 WHEN IT RAINED 0.09 INCHES. THERE WERE TRACE EVENTS --
MEANING LESS THAN 0.01 INCH -- AT SEATAC ON JUNE 29 AND JULY 13.

THE SHORTWAVE WELL MOVE FURTHER EAST SUNDAY...AND ANOTHER UPPER
SHORTWAVE WILL APPROACH THE AREA FROM OFFSHORE. MOIST ONSHORE FLOW
WILL MAINTAIN A THREAT OF LIGHT SHOWERS...BUT SUNDAY LOOKS DRIER AND
PARTLY SUNNY.   MCDONNAL

.LONG TERM...HERE IS THE LONG TERM SECTION FROM THE EARLY MORNING
FORECAST DISCUSSION -- 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....WEST TO NORTHWEST FLOW ALOFT WILL PREVAIL TODAY AND
TONIGHT. AT THE SURFACE...ONSHORE FLOW WILL CONTINUE WITH HIGH
PRESSURE OFFSHORE AND LOWER PRESSURE INLAND. THE AIR MASS IS STABLE
WITH LOW LEVEL MOISTURE...MORE WIDESPREAD WEST OF PUGET SOUND.

LOW CLOUDS SHOULD BURN PARTIALLY BACK TO THE COAST THIS AFTERNOON.
LOW AND MID LEVEL MOISTURE SHOULD INCREASE ALL AREAS AFTER MIDNIGHT
TONIGHT AS AN UPPER LEVEL WEATHER SYSTEM BEGINS TO MOVE INTO THE
AREA.

KSEA...THERE WILL BE CEILINGS IN THE 1000-2000 FOOT RANGE AT TIMES
AT TIMES THIS MORNING UNTIL AROUND NOON...WITH LOW CLOUDS EXPECTED
TO BURN OFF AFTER THAT. MID LEVEL CLOUDS SHOULD DEVELOP AFTER
MIDNIGHT TONIGHT WITH LOW CLOUDS REACHING THE TERMINAL LATE TONIGHT.
SOUTHERLY WIND 4-8 KNOTS...WITH A FEW HOURS OF WEST OR NORTHWEST
POSSIBLE LATE THIS AFTERNOON AND EARLY THIS EVENING. SCHNEIDER

&&

.MARINE...ONSHORE FLOW WILL INCREASE DIURNALLY THIS AFTERNOON AND
EVENING. THIS IS EXPECTED TO BRING GALE FORCE WEST WINDS TO THE
CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA WITH SMALL CRAFT ADVISORY
WESTERLY WINDS TO THE ADJACENT INLAND WATERS.

A WEAK UPPER TROUGH WILL MOVE THROUGH THE WATERS SATURDAY. SMALL
CRAFT ADVISORY SOUTHERLY WINDS ARE POSSIBLE FOR SOME OF THE WATERS
AS THIS SYSTEM MOVES THROUGH.

AN ONSHORE FLOW PATTERN WILL PREVAIL SUNDAY THROUGH TUESDAY WITH
HIGH PRESSURE OFFSHORE AND LOWER PRESSURE INLAND. SCHNEIDER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...GALE WARNING CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA.
    .SMALL CRAFT ADVISORY COASTAL WATERS...NORTHERN INLAND WATERS...
     AND ADMIRALTY INLET.

&&

$$

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




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