Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 160953
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
252 AM PDT TUE SEP 16 2014

.SYNOPSIS...ONSHORE FLOW WILL BRING COOLER TEMPERATURES TO WESTERN
WASHINGTON TODAY ALONG WITH AREAS OF MORNING LOW CLOUDS. AN UPPER
LEVEL TROUGH WILL BRING A CHANCE OF SHOWERS TO THE AREA WEDNESDAY
THROUGH FRIDAY NIGHT...WITH SHOWERS MOST LIKELY ON THURSDAY. AN
UPPER LEVEL RIDGE WILL BUILD OVER THE REGION THIS WEEKEND FOR WARMER
AND DRY WEATHER.

&&

.SHORT TERM...A SW MARINE PUSH OVERNIGHT HAS BROUGHT AREAS OF
STRATUS INLAND THIS MORNING. STRATUS REACHED SHELTON AROUND MIDNIGHT
AND WITH KSHN WINDS BLOWING SW 15-25KT SHOULD SPREAD THE LOW CLOUDS
ACROSS MOST OF PUGET SOUND THIS MORNING. THE SMALL UPPER LEVEL
TROUGH THAT HAS TRIGGERED THE MARINE PUSH WAS CENTERED OVER ASTORIA
AT 09Z/2 AM AND WAS HEADED QUICKLY NORTH. A SMALL AREA OF SHOWERS
WAS ALONG THE N OREGON COAST ALONG WITH A SOLO LIGHTNING STRIKE AT
0745Z. THIS SHOWER AREA IS SMALL ENOUGH TO FIZZLE OUT THIS MORNING
AS THE UPPER LEVEL TROUGH MOVES DEEPER INTO THE UPPER LEVEL RIDGE
CENTERED OVER THE PACNW...BUT STILL BEARS WATCHING.

THE NAM12 AND ARW-W BOUNDARY LAYER RH FORECASTS SEEMED A REASONABLE
INDICATOR FOR STRATUS COVERAGE TODAY. LOW CLOUDS WILL PROBABLY
BLANKET PUGET SOUND THIS MORNING WITH A LITTLE BIT SPREADING E OF
LAKE WASHINGTON...BUT SHOULD BURN OFF OVER THE SOUND THIS AFTERNOON.
HOWEVER THE STRATUS WILL BE DEEP ENOUGH ALONG THE COAST AND ONSHORE
FLOW PERSISTENT ENOUGH SO THAT STRATUS WILL PROBABLY NOT BURN OFF
OVER THE LOWER CHEHALIS VALLEY TODAY. THE RATHER SPARSE MID AND HIGH
CLOUDS FROM THE UPPER LEVEL TROUGH WILL NOT ADD MUCH TO THE OVERALL
CLOUD COVER. MAX TEMPS WILL BE A LITTLE TRICKY TODAY...WITH STRONGER
COOLING EXPECTED IN THE STRATUS AREAS...ESPECIALLY ALONG THE COAST
AND OVER THE LOWER CHEHALIS.

MAX TEMPS WEDNESDAY WERE ALSO TROUBLESOME. THE ONSHORE FLOW WILL BE
ABOUT AS STRONG TONIGHT AND WEDNESDAY MORNING. THE MARINE LAYER WILL
BE DEEPER AND WILL SPREAD ACROSS MOST OF W WA...BUT INSTABILITY FROM
THE UPPER LEVEL TROUGH APPROACHING FROM OFFSHORE SHOULD HELP THE
CLOUD COVER BREAK UP A BIT WEDNESDAY AFTERNOON. FOR MAX TEMPS THIS
MEANS THAT LOCATIONS TODAY WHERE THE STRATUS IS MOST PERSISTENT
COULD VERY WELL BE SLIGHTLY WARMER ON WEDNESDAY GIVEN A BETTER MIXED
MARINE LAYER. LOCATIONS THAT ARE STRATUS FREE TODAY...MAY END UP
BEING A LITTLE COOLER BECAUSE OF THE GREATER COVERAGE OF CLOUDS ON
WEDNESDAY.

OVERALL THE MODELS REMAIN IN GENERAL AGREEMENT WITH THE LARGE UPPER
LEVEL TROUGH CURRENTLY OFFSHORE ALONG 140W EJECTING E THIS WEEK.
SPOTTY SHOWERS WILL PROBABLY SPREAD TO THE COAST WEDNESDAY MORNING
AND THEN INLAND WEDNESDAY AFTERNOON. THE UPPER LEVEL TROUGH AXIS
WILL MOVE ACROSS THE AREA WEDNESDAY EVENING AND THURSDAY MORNING FOR
THE GREATEST SHOWER POTENTIAL AND LIKELY POPS. THURSDAY SHOULD BE
THE COOLEST DAY WITH THE COOLER AIR MASS FROM THE TROUGH RIGHT
OVERHEAD. KAM

.LONG TERM...THE UPPER LEVEL TROUGH WILL MOVE OVER E WA THURSDAY
EVENING WITH DIMINISHING SHOWERS OVER W WA. HOWEVER ANOTHER WEAKER
UPPER LEVEL SHORTWAVE TROUGH MOVING ONSHORE WILL PROLONG THE CHANCE
OF SHOWERS INTO FRIDAY EVENING. GFS AND ECMWF AGREE WELL ON BUILDING
A STRONG UPPER LEVEL RIDGE JUST OFFSHORE FRIDAY NIGHT THEN MOVING IT
INLAND ON SATURDAY. THIS WILL BRING ANOTHER PERIOD OF E-NE LOW LEVEL
OFFSHORE FLOW...WHICH COULD PUSH MAX TEMPS BACK UP INTO THE 80S THIS
WEEKEND...PARTICULARLY ON SUNDAY. BOTH MODELS HAVE THE RIDGE
SHIFTING E OVER W MT SUNDAY NIGHT ALLOWING A WEAKENING FRONT TO
APPROACH THE COAST ON MONDAY. HOWEVER THE FRONT COULD BE WEAK AND
SLOW ENOUGH TO EKE OUT A MOSTLY SUNNY DRY MONDAY AS WELL. KAM

&&

.AVIATION...LOW CLOUDS COAST AND AREAS OF LOW CLOUDS IN PUGET SOUND
THIS MORNING. SOME OF THE MARINE STRATUS MAY PUSH EAST IN THE STRAIT
THIS MORNING BUT MORE LIKELY WILL HOLD OFF TIL THE STRONGER PUSH
THIS AFTERNOON. IN THE AREAS THAT DO NOT SEE MORNING LOW
CLOUDS...MAINLY NORTH OF EVERETT...THERE WILL ONLY BE SOME MID AND
HIGH CLOUDS. THE RIDGE IS MOVING EAST AND THERE IS SW FLOW ALOFT.
AREAS OF LOW CLOUDS SHOULD DEVELOP AGAIN TONIGHT AND WED MORNING.

KSEA...MORNING LOW CLOUDS ARE EXPECTED...THEN JUST SOME MID AND HIGH
CLOUDS. WITH ONSHORE FLOW THE BREEZE WILL REMAIN S TO SW.

&&

.MARINE...ONSHORE FLOW...AND A DECENT WLY PUSH IS LIKELY IN THE
STRAIT OF JUAN DE FUCA THIS AFTERNOON AND EVENING. AFTER THE MARINE
PUSH TODAY THE ONSHORE FLOW WILL BE FAIRLY LIGHT AS WEATHER SYSTEMS
MOVING THROUGH THE AREA ARE EXPECTED TO BE RATHER WEAK.

&&

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

&&

$$

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