Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 271552
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT WED AUG 27 2014

.SYNOPSIS...HIGH PRESSURE ALOFT AND WEAK ONSHORE FLOW WILL RESULT IN
ANOTHER MOSTLY SUNNY WARM DAY FOR WESTERN WASHINGTON TODAY. THE
MARINE LAYER WILL DEEPEN TONIGHT AND A SMALL UPPER TROUGH WILL MOVE
THROUGH AREA THURSDAY FOR CLOUDIER COOLER WEATHER. ANOTHER LARGER
UPPER TROUGH WILL BRING A CHANCE OF SHOWERS FRIDAY THROUGH THIS
WEEKEND...AND THAT PATTERN WILL PROBABLY CONTINUE EARLY NEXT WEEK.

&&

.SHORT TERM...ZONAL FLOW WILL CONTINUE OVER THE AREA TODAY AS AN
UPPER LEVEL RIDGE MOVES EAST OUT OF THE AREA. ANY REMAINING LOW
CLOUDS AND FOG WILL CLEAR OUT FOR MOSTLY SUNNY SKIES AND WARM TEMPS
THROUGHOUT THE AREA BY THIS AFTERNOON. EXPECT A SLIGHTLY COOLER DAY
THAN YESTERDAY BY ABOUT 5 DEGREES.

A MORE DRAMATIC CHANGE WILL OCCUR TONIGHT AND THURSDAY. ONSHORE FLOW
WILL INCREASE AND THE MARINE LAYER WILL DEEPEN TONIGHT...WITH
STRATUS PUSHING WELL INLAND OVERNIGHT. THEN A SMALL UPPER SHORTWAVE
WILL MOVE THROUGH THE AREA THURSDAY. THERE COULD BE SOME DRIZZLE
ALONG THE COAST IN THE MORNING...AND SOME SHOWERS IN THE NORTH
CASCADES IN THE AFTERNOON. FOR WESTERN WASHINGTON ON THE WHOLE...IT
WILL JUST BE A MOSTLY CLOUDY AND COOLER DAY.

THIS TREND WILL CONTINUE THURSDAY NIGHT AND FRIDAY...WITH THE FLOW
ALOFT BACKING TO SOUTHWESTERLY AS A LARGER UPPER TROUGH MOVES INTO
THE OFFSHORE WATERS. LOW LEVEL FLOW WILL REMAIN ONSHORE...WITH A
FAIRLY DEEP MARINE LAYER OVER WESTERN WASHINGTON. FRIDAY WILL BE
ANOTHER MOSTLY CLOUDY DAY AND EVEN COOLER THAN THURSDAY. SHOWERS ARE
POSSIBLE LATE FRIDAY AND FRIDAY NIGHT...ESPECIALLY AT THE COAST AND
IN THE MOUNTAINS. JSMITH

.LONG TERM...THE UPPER TROUGH WILL MOVE INLAND SATURDAY...AND THIS
DAY HAS THE BEST CHANCE FOR WIDESPREAD SHOWERS. THE NORTH COAST...
OLYMPICS...AND NORTH CASCADES IN PARTICULAR SHOULD HAVE
PRECIPITATION...WITH A CHANCE EVERYWHERE ELSE. THE LONG WAVE UPPER
TROUGH AXIS WILL MOVE WELL EAST OF THE CASCADES SATURDAY NIGHT...BUT
IT LOOKS INCREASINGLY LIKELY THAT SEVERAL SHORTWAVES WILL AFFECT
WESTERN WASHINGTON SUNDAY THROUGH TUESDAY. THE MODELS DIFFER ON THE
TIMING AND STRENGTH OF THESE FEATURES THOUGH...SO FOR NOW WE CAN
REALISTICALLY ONLY FORECAST A BROAD BRUSH CHANCE OF SHOWERS FOR THAT
PERIOD. THE GFS SHOWS AN ESPECIALLY COOL AND WET SOLUTION FOR
TUESDAY...BUT THE EUROPEAN AND CANADIAN MODELS WAIT TILL WEDNESDAY
TO BRING IN A WEAKER UPPER TROUGH.   MCDONNAL/JSMITH

&&

.AVIATION...WEAK HIGH PRES OVER THE REGION WILL MAINTAIN DRY AND
STABLE CONDITIONS ACROSS WESTERN WA TODAY. FLOW ALOFT WILL REMAIN
WESTERLY THROUGH THURSDAY. THE LOW LEVEL STRATUS CLOUDS THAT FORMED
OVER THE COAST...STRAIT AND LOWER CHEHALIS VALLEY THIS MORNING
CONTINUE TO PRODUCE IFR CONDITIONS FOR THOSE AREAS. EXPECT LOW
CLOUDS TO BURN OFF BY EARLY AFTERNOON...BECOMING VFR ALL ARES.
CLOUDS WILL INCREASE TONIGHT AHEAD OF AN APPROACHING COLD FRONT
APPROACHES. THIS SYSTEM MAY BRING LIGHT RAIN OR DRIZZLE...MAINLY TO
THE COAST AND NORTH WASHINGTON CASCADES THURSDAY.

KSEA...VFR CONDITIONS WILL PREVAIL TODAY. LIGHT WINDS AT THE SURFACE
WILL BECOME NORTHERLY THIS AFTERNOON.

&&

.MARINE...HIGH PRES OVER THE NE PAC WILL MAINTAIN ONSHORE FLOW
ACROSS WESTERN WA. HIGHEST WINDS AND WAVES ARE EXPECTED THROUGH THE
CENTRAL AND EAST STRAIT OF JUAN DE FUCA DURING THE LATE AFTERNOON
AND EVENING HOURS. A WEAK COLD FRONT WILL CROSS WESTERN WA ON
THU...FOLLOWED BY ANOTHER WEAK SYSTEM ON FRI. THE FLOW WILL REMAIN
ONSHORE THROUGH THE WEEKEND.

&&

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

&&

$$

WWW.WEATHER.GOV/SEATTLE

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








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