Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 170328
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
830 PM PDT TUE SEP 16 2014

.SYNOPSIS...LOWER PRESSURE ALOFT WILL BRING A THREAT OF SHOWERS INTO
FRIDAY WITH SHOWERS MOST LIKELY WEDNESDAY NIGHT AND THURSDAY. HIGHER
PRESSURE ALOFT IS FORECAST TO BUILD OVER THE REGION THIS WEEKEND FOR
A RETURN TO WARMER AND DRIER WEATHER.

&&

.SHORT TERM...UPPER TROUGH WAS APPROACHING 135W FROM THE WEST THIS
EVENING WITH THE DOWNSTREAM UPPER RIDGE OVER THE NORTHERN ROCKIES.
SOUTHERLY FLOW ALOFT OVER WA WITH EMBEDDED SHORTWAVES AND SPOTTY
LIGHT SHOWERS IN THE MID AND HIGH LEVEL MOISTURE. THE KSLE AND KUIL
RAOBS SHOW THE AIR MASS IS GETTING MORE MOIST - PRIMED IF YOU WISH.
WILL UPDATE THE EVENING FORECAST TO REFLECT A SMALL THREAT OF LIGHT
SHOWERS OVERNIGHT INTO WED MORNING.

THE LOW LEVEL ONSHORE FLOW IS NOW MAINLY WEST TO EAST WITH STRONGER
GRADIENTS ACROSS THE CASCADES. WITH THE MID AND HIGH LEVEL CLOUDS
PRESENT...MARINE CLOUDS WED MORNING WILL LIKELY BE MORE LIMITED IN
BOTH SPACE AND TIME.

00Z PROGS IN THUS FAR CONTINUE THE TREND OF TRACKING THE UPPER
TROUGH ONSHORE BY THU THOUGH WEAKENING WITH TIME. BEST THREAT OF
SHOWERS APPEARS TO BE THE 12 HOUR PERIOD FROM 06Z-18Z THURSDAY. THEN
THE WESTERLY FLOW ALOFT SHOULD LIMIT WHAT SHOWERS ARE LEFT IN THE
MOUNTAINS.

HIGH TEMPS TODAY WERE DOWN ABOUT 10-20 DEGREES FROM MONDAY.
WEDNESDAY AND THURSDAY HIGHS SHOULD BE A BIT BELOW MID SEPTEMBER
SEASONAL READINGS.

SATELLITE IMAGERY MUCH FURTHER WEST ACROSS THE NORTH PACIFIC SHOWS A
STRONG SHORTWAVE NEAR 150E THAT IS EXPECTED TO ZIP UNDER THE
ALEUTIAN UPPER LOW AND HELP BUILD RIDGING OVER OUR REGION BY THE END
OF THE WEEK. BUEHNER

.LONG TERM...FROM THE PREVIOUS DISCUSSION...THE WEEKEND WILL SEE A
STRONG UPPER RIDGE WITH OFFSHORE SURFACE FLOW. MODEL HEIGHTS ARE IN
THE MID 580S. THIS IS A SUNNY AND WARM PATTERN. FOR NOW HAVE BOOSTED
TEMPS INTO THE 70S AND LOW 80S FOR SATURDAY. FOR SUNDAY THE FORECAST
CALLS FOR MORE WIDESPREAD 80S. ON MONDAY SURFACE FLOW TURNS WEAKLY
ONSHORE AND HEIGHTS FALL IN RESPONSE TO AN APPROACHING SYSTEM.
MONDAY IS LIKELY TO REMAIN DRY BUT CLOUDS WILL INCREASE MONDAY NIGHT
AND A CHANCE OF SHOWERS APPEARS IN THE TUESDAY FORECAST. BURKE

&&

.AVIATION...AN UPPER TROUGH WILL APPROACH THE PACNW WED. SW FLOW
ALOFT WITH MAINLY INCREASING MID LEVEL MOISTURE. STRATUS MAINLY ON
THE COAST...BUT SOME AREAS OF MARINE STRATUS MAY PUSH INTO THE
INTERIOR BY DAYBREAK WED.

KSEA...MAINLY MID LVL CLOUDS...INCREASING AND THICKENING. THERE IS A
CHANCE OF LOW CLOUDS PUSHING IN FROM THE COAST...BUT IF IT MAKES IT
ONLY FOR A COUPLE OR THREE HOURS THROUGH MID MORNING WED.

&&

.MARINE...ONSHORE FLOW WILL BECOME FAIRLY LIGHT THROUGH WED AND THU
AS WEATHER SYSTEMS MOVING THROUGH THE AREA ARE EXPECTED TO BE RATHER
WEAK. OFFSHORE FLOW DEVELOPS SAT AND SUN WITH BREEZY EAST WINDS
DEVELOPING AT THE W ENTRANCE TO THE STRAIT OF JUAN DE FUCA THIS
WEEKEND.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA
     THROUGH MIDNIGHT TONIGHT.

&&

$$

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