Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 191030
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
330 AM PDT TUE AUG 19 2014

.SYNOPSIS...A LOW PRESSURE SYSTEM ALOFT WILL INFLUENCE THE WEATHER
PATTERN OVER THE AREA THROUGH THURSDAY. THIS WILL RESULT IN
SOMEWHAT UNSETTLED CONDITIONS. THE MAIN IMPACTS WILL BE COOLER
TEMPERATURES AND CLOUDIER SKIES.

&&

.SHORT TERM...
AN UPPER TROF WAS MOVING OVER THE REGION AT THIS TIME. THIS
SYSTEM WAS SLIGHTLY STRONGER THAN WHAT THE MODELS HAD ADVERTISED
AND HAS TRIGGERED ISOLATED TSTMS OVER THE NORTHERN PART OF THE CWA
EARLY THIS MORNING. THERE IS A POSSIBILITY THAT THIS ACTIVITY
MIGHT BECOME A LITTLE MORE WIDESPREAD DURING THE NEXT FEW HOURS...
THUS WILL KEEP AN EYE ON IT. IN THE MEANTIME...THE RISK OF TSTMS
HAS BEEN CONFINED TO THE NORTHERN ZONES FOR NOW.

WESTERN WA WILL REMAIN UNDER THE INFLUENCE OF AN UPPER TROF DURING
THIS PERIOD FOR SOMEWHAT UNSETTLED CONDITIONS. THE MAIN IMPACTS
WILL BE COOLER TEMPS AND MORE CLOUD COVER. HOWEVER THERE WILL BE A
CHANCE OF PRECIP OVER PARTS OF THE CWA EACH DAY.

THE SURFACE ONSHORE PRESSURE GRADIENT WILL TIGHTEN THIS AFTERNOON...
LEADING TO THE DEVELOPMENT OF A PUGET SOUND CONVERGENCE ZONE
/PSCZ/ LATER THIS AFTERNOON. THE PSCZ SHOULD PERSIST OVERNIGHT.
THE NAM AND WRF-GFS DIFFERED ON THE EXACT PLACEMENT OF THE
PSCZ...SO BROAD-BRUSHED THE FORECAST TO INDICATE THAT THE PSCZ
WILL AFFECT THE NORTHERN AND CENTRAL PUGET SOUND REGION. LATER
SHIFTS CAN FINE-TUNE THE FORECAST IF NEEDED. THE ONSHORE FLOW WILL
TIGHTEN ON THU AFTER RELAXING SOME ON WED...RESULTING IN THE
REDEVELOPMENT OF A PSCZ.

.LONG TERM...
CONFIDENCE IN THIS PERIOD WAS NOT VERY HIGH DUE TO DISAGREEMENT IN
THE MEDIUM RANGE SOLUTIONS. FOR EXAMPLE...THE GFS HAD THE REGION
MORE UNDER THE INFLUENCE OF AN UPPER TROF LATE IN THE PERIOD
WHEREAS THE ECMWF KEPT AN UPPER RIDGE OVER THE AREA. THE CURRENT
FORECAST REFLECTS CLIMO...WHICH IS PROBABLY A GOOD WAY TO GO FOR
NOW.

&&

.AVIATION...A BROAD UPPER LEVEL TROUGH WILL SETTLE OVER THE PACIFIC
NORTHWEST TODAY AND TONIGHT WITH WEST TO NORTHWEST FLOW ALOFT. AT
THE SURFACE...ONSHORE FLOW WILL PREVAIL WITH HIGH PRESSURE OFFSHORE
AND LOWER PRESSURE INLAND. AIR MASS STABLE.

STRATUS AT THE COAST WILL SPREAD PARTIALLY INLAND THROUGH THE
CHEHALIS GAP THIS MORNING. A STRONGER PUSH IS EXPECTED TONIGHT WITH
MORE EXTENSIVE LOW CLOUDS FOR THE INTERIOR BY WEDNESDAY MORNING.

A PUGET SOUND CONVERGENCE ZONE WILL LIKELY FORM OVER KING OR
SOUTHERN SNOHOMISH COUNTY LATE THIS AFTERNOON...LINGER INTO THE
EVENING...THEN WEAKEN AFTER MIDNIGHT TONIGHT.

KSEA...COASTAL STRATUS WILL PROBABLY NOT MAKE IT TO THE TERMINAL
THIS MORNING. A CONVERGENCE ZONE COULD BRING SOME LOWER CEILINGS
LATE THIS AFTERNOON AND EVENING. LOW CLOUDS ARE EXPECTED LATER
TONIGHT. SOUTH TO SOUTHWEST WIND 3-6 KNOTS. WINDS COULD SWITCH TO
NORTH FOR A FEW HOURS THIS EVENING IF THE CONVERGENCE ZONE COMES
DOWN. SCHNEIDER

&&

.MARINE...ONSHORE FLOW WILL PREVAIL FOR THE NEXT SEVERAL DAYS WITH
HIGH PRESSURE OFFSHORE AND LOWER PRESSURE INLAND. A WEAK UPPER LEVEL
DISTURBANCES PASSING TO THE NORTH TODAY WILL CAUSE THE ONSHORE FLOW
TO INCREASE.

SMALL CRAFT ADVISORY WEST WINDS ARE LIKELY EACH EVENING FOR THE NEXT
SEVERAL DAYS OVER THE CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA.
THE WINDS IN THE STRAIT SHOULD BE STRONGEST TONIGHT. THE CURRENT
FORECAST FOR TONIGHT FOR THE CENTRAL AND EAST EASTERN STRAIT IS FOR
HIGH END SMALL CRAFT ADVISORY STRENGTH BUT THERE IS A CHANCE IT
COULD HIT GALE. THERE SHOULD ALSO BE SOME SMALL CRAFT ADVISORY WINDS
OVER THE INLAND WATERS ADJACENT TO THE STRAIT THIS EVENING.

LASTLY...THERE WILL BE SMALL CRAFT ADVISORY NORTHWEST WINDS OVER THE
OUTER COASTAL WATERS AT TIMES FOR THE NEXT COUPLE OF DAYS. SCHNEIDER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY IN EFFECT FOR THE COASTAL WATERS FROM
     JAMES ISLAND TO CAPE SHOALWATER FROM 10 NM OUT TO 60 NM...
     THE CENTRAL/EASTERN STRAIT OF JUAN DE FUCA...THE NORTHERN
     INLAND WATERS AND ADMIRALTY INLET.

&&

$$

WWW.WEATHER.GOV/SEATTLE

FOR THE GRAPHICAL AFD...VISIT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML



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