Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 312236
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
334 PM PDT SUN AUG 31 2014

.SYNOPSIS...STRONG WESTERLY FLOW ALOFT OVER THE AREA WILL HELP KEEP
LINGERING SHOWERS OVER THE CASCADES THIS EVENING. A WEAK SYSTEM THAT
WILL BRUSH THE AREA FROM THE NORTH WILL BRING A CHANCE OF LIGHT RAIN
TO THE COAST LATE TONIGHT...THEN THE NORTH DURING THE MORNING AND
AFTERNOON HOURS ON LABOR DAY. HIGH PRESSURE ALOFT WILL BUILD BRIEFLY
OVER WESTERN WASHINGTON IN THE AFTERNOON AND EVENING...FOLLOWED BY A
STRONGER AND COLDER SYSTEM THAT WILL IMPACT THE AREA ON TUESDAY.
RISING UPPER LEVEL HEIGHTS WEDNESDAY WILL USHER IN A DRIER AND
WARMER PERIOD THAT WILL PERSIST THROUGH THE WEEKEND.

&&

.SHORT TERM...THE UPPER LEVEL JET AND STRONG WESTERLY FLOW ALOFT
WILL KEEP THE THREAT OF SHOWERS MAINLY OVER THE CASCADES TONIGHT AS
HEIGHTS RISE BRIEFLY OVER THE REGION AHEAD OF A WEAK SYSTEM THAT
WILL BRUSH THE AREA FROM THE NORTH LATE TONIGHT INTO MONDAY MORNING.
MODELS CONTINUE TO SHOW THIS SYSTEM ALL BUT FALL APART AS IT MOVES
INTO HAIDA GUAII AND BRITISH COLUMBIA THIS EVENING. HAVE BACKED OFF
ON PRECIPITATION THIS EVENING FOR THE AREA WITH A CHANCE OF RAIN
MAINLY FOR THE NORTH COAST AFTER MIDNIGHT AS THE TAIL END OF THE
WEAK FRONT APPROACHES FROM THE WEST. ESSENTIALLY ALL MODELS SHOW
THIS BOUNDARY COMPLETELY COLLAPSE AS IT MOVES ONSHORE...BRUSHING THE
NORTH WITH LIMITED PRECIPITATION THROUGH THE MORNING AND INTO THE
AFTERNOON. OTHERWISE EXPECT MORNING CLOUDS TO GIVE WAY TO PARTLY
SUNNY AND DRY SKIES WITH NEAR NORMAL TEMPERATURES.

MODELS REMAIN IN GOOD AGREEMENT ON THE NEXT SYSTEM...EJECTING A
VIGOROUS SHORTWAVE TROUGH FROM CENTRAL ALASKA INTO THE GULF OF
ALASKA EARLY LABOR DAY MORNING. THIS SYSTEM IS FORECAST TO DIG SOUTH
AND EAST ALONG THE BRITISH COLUMBIA COAST MONDAY AND MONDAY NIGHT
BEFORE REACHING WASHINGTON TUESDAY MORNING. THE BEST CHANCE OF
PRECIPITATION WILL BE ACROSS THE NORTHERN HALF OF THE AREA WITH MUCH
COOLER TEMPERATURES. DAYTIME TEMPS WILL RUN 5-10 DEGREES COOLER THAN
MONDAY WHILE SNOW LEVELS WILL FALL TO JUST BELOW 6000 FEET LATE
TUESDAY NIGHT AND EARLY WEDNESDAY MORNING OVER THE NORTH CASCADES.
LOCALLY BREEZY CONDITIONS ARE POSSIBLE TUESDAY AFTERNOON.


.LONG TERM...MEDIUM RANGE MODELS ALL AGREE ON THE ZONAL FLOW OVER
THE NORTHEAST PACIFIC BUCKLING INTO A HIGHER AMPLITUDE PATTERN BY
MIDWEEK. THIS PATTERN WILL BE ANCHORED BY A LARGE SCALE RIDGE THAT
WILL BUILD ALONG 140W TUESDAY AND INTO BRITISH COLUMBIA BY WEDNESDAY
NIGHT. MODELS DO DISAGREE ON THE FLOW DOWNSTREAM OF THE RIDGE ON
FRIDAY WITH VARYING DEGREES OF SPLIT FLOW ALOFT OVER THE NORTHWEST
AND A WEAK UPPER LEVEL LOW OVER THE GREAT BASIN OR CENTRAL ROCKY
MOUNTAINS. NONETHELESS THE LARGE SCALE PATTERN WILL KEEP THE PACIFIC
NORTHWEST DRIER AND WARMER BEGINNING WEDNESDAY AFTERNOON AND
PERSISTING THROUGH THE WEEKEND. MODELS GENERALLY AGREE ON A SYSTEM
RIDING OVER THE TOP RIDGE AND INTO THE NORTHWEST LATE SUNDAY INTO
MONDAY MORNING.

&&

.AVIATION...NW FLOW ALOFT. LIGHT LOW LEVEL ONSHORE FLOW. AIR IS
MOIST. A WEAK WEATHER SYSTEM WILL DISSIPATE AS IT REACHES THE WA
COAST MONDAY. LIGHT ISOLATED SHOWERS FROM AFTERNOON CUMULUS WILL
GIVE WAY TO AREAS OF FAIRLY LOW STRATUS OVERNIGHT. MORNING LOW
CLOUDS ON MONDAY WILL LIFT INTO THE AFTERNOON AND SOME MOISTURE
ARRIVES WITH THE NEXT WEAK SYSTEM.

KSEA...AFTER SOME CLEARING THROUGH THIS EVENING LOW CLOUDS WILL
DEVELOP OVERNIGHT FOR ANOTHER CLOUDY MORNING ON MONDAY.

&&

.MARINE...A WEAK SYSTEM WILL DISSIPATE AS IT REACHES THE COAST
MONDAY...GIVING A SLY BREEZE OVER THE COASTAL WATERS. THEN BY THE
MIDDLE OF THE WEEK A MORE SUMMERY WIND REGIME WILL SET UP WITH A
TYPICAL NW BREEZE EACH DAY.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&

$$

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