Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 302235
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
333 PM PDT SAT AUG 30 2014

.SYNOPSIS...AN UPPER LEVEL TROUGH MOVING OUT OF WESTERN WASHINGTON
THIS EVENING WILL KEEP A FEW LINGERING SHOWERS OVER THE AREA THIS
EVENING. WEAK UPPER LEVEL RIDGING WILL BUILD OVER WESTERN WASHINGTON
TONIGHT BRINGING DRIER CONDITIONS TO MUCH OF THE AREA THROUGH
SUNDAY. ANOTHER RELATIVELY WEAK FRONTAL SYSTEM WILL BEGIN TO AFFECT
THE REGION SUNDAY NIGHT INTO LABOR DAY MORNING. HIGH PRESSURE
ALOFT WILL BUILD OVER THE AREA DURING THE AFTERNOON ON LABOR DAY
FOLLOWED BY ANOTHER WEAK SYSTEM LATER TUESDAY.

&&

.SHORT TERM...THE UPPER LEVEL THAT MOVED OVER WESTERN WASHINGTON
EARLIER TODAY WILL CONTINUE TO SHIFT EAST OF THE CASCADES THIS
EVENING. SHOWERS HAVE GENERALLY TAPERED OFF THIS AFTERNOON...WITH A
FEW OF THE MORE ORGANIZED BANDS OF PRECIPITATION LINGERING SOUTH OF
THE KING COUNTY/SNOHOMISH COUNTY LINE INTO THE SOUTHWEST INTERIOR.
PRECIPITATION WILL CONTINUE TO TAPER OFF THIS EVENING AS THE UPPER
LEVEL LOW CONTINUES TO SLIDE EAST. BOTH THE NAM12 AND UW WRF RUNS DO
SHOW A WEAK PSCZ FORMING OVER THE I90 CORRIDOR THIS EVENING. THIS
MAY KEEP A FEW SHOWERS OVER THE LOWLANDS...OTHERWISE EXPECT SHOWERS
TO RETREAT TO THE CASCADES AS HIGH PRESSURE BUILDS ALOFT OVER THE
REGION TONIGHT THROUGH SUNDAY MORNING. BY EARLY SUNDAY MORNING THE
THREAT OF SHOWERS WILL BE LIMITED MAINLY TO THE CASCADES.

THE NEXT SYSTEM WILL BEGIN TO AFFECT THE AREA SUNDAY EVENING INTO
MONDAY MORNING. MODEL RUNS CONTINUE TREND TOWARDS A SLOWER...AND
MUCH WEAKER SOLUTION WITH THIS SYSTEM. BRINGING PRECIPITATION INTO
WESTERN WASHINGTON LATE SUNDAY NIGHT AND THE FRONT ONSHORE EARLY
MONDAY MORNING. NEARLY ALL THE MODELS NOW SHOWING THIS FRONT
ESSENTIALLY FALLING APART AS IT MOVES ONSHORE. HAVE TRENDED POPS AND
PRECIP BACK...CONTINUING TO HIGHLIGHT THE BEST CHANCE FOR
PRECIPITATION AFTER MIDNIGHT SUNDAY NIGHT INTO EARLY MONDAY MORNING
FOLLOWED BY DRYING DURING THE AFTERNOON AS AN UPPER RIDGE TAKES
BRIEF HOLD OF THE AREA. SOLID ONSHORE FLOW THROUGH THE PERIOD WILL
KEEP TEMPERATURES NEAR OR SLIGHTLY BELOW NORMAL.

.LONG TERM...OVERALL CONFIDENCE FOR THE BIG PICTURE IN THE EXTENDED
PERIOD A BIT HIGHER THAN OVERNIGHT. MEDIUM RANGE MODELS CONTINUE TO
SHOW AN UPPER LEVEL TROUGH MOVING INTO THE REGION TUESDAY AFTERNOON
AND EVENING BRINGING ANOTHER ROUND OF SHOWERS TO THE REGION THROUGH
EARLY WEDNESDAY MORNING. MODELS ALL SHOW THE ZONAL FLOW OVER THE
NORTHEAST PACIFIC BREAKING DOWN AT THIS POINT INTO A HIGHER
AMPLITUDE PATTERN AS A RIDGE BUILDS INTO THE GULF OF ALASKA. MODELS
NOW IN BETTER AGREEMENT ON THE DOWNSTREAM DEVELOPMENT OF DRY SPLIT
FLOW OVER PACIFIC NORTHWEST THURSDAY FOLLOWED BY THE LARGE SCALE
RIDGE SHIFTING EAST FRIDAY THROUGH THE WEEKEND WITH CONTINUED DRY
AND WARMER WEATHER.

&&

.AVIATION...THE CLOUDS AND AREAS OF RAIN WILL SHIFT INLAND THROUGH
THE AFTERNOON AND EVENING. A LITTLE SUNSHINE ON THE COAST OUGHT TO
WORK INLAND SOMEWHAT...AND SUNBREAKS ARE NOT A BAD BET FOR THE
INLAND PORTION OF WRN WA EARLY THIS EVENING. THE UW WRFGFS SUGGESTS
A FEW SHOWERS LINGERING AROUND SEATTLE...PERHAPS IN A WEAK PSCZ.
ONSHORE FLOW TONIGHT AND THE MARINE LAYER ARE LIKELY TO GIVE MORNING
CLOUDS ON SUNDAY...PERHAPS GIVING WAY TO PARTLY SUNNY SKIES SUNDAY
AFTERNOON AND EVENING. THE FLOW ALOFT WILL TURN FROM WSW THIS
AFTERNOON TO WNW ON SUNDAY.

KSEA...SCATTERED SHOWERS WITH THE WEAK SYSTEM MOVING THROUGH WRN WA
THIS AFTERNOON COULD LINGER INTO THE EARLY PART OF THE EVENING...BUT
WE MAY SEE SOME SUNBREAKS AS WELL. OVERNIGHT LOW CLOUDS OUGHT TO SET
UP FOR MORNING LOW CLOUDS ON SUNDAY AND THEN SOME CLEARING IN THE
AFTERNOON.

&&

.MARINE...THE WEAK LOW PRESSURE CENTER WAS OVER SW WA THIS
AFTERNOON. ONSHORE FLOW SHOULD INCREASE THIS EVENING...AND THE
WRFGFS GIVES WINDS REACHING WESTERLY SMALL CRAFT ADVISORY STRENGTH
IN THE CENTRAL/EASTERN STRAIT. THE NEXT WEATHER SYSTEM FOR SUN NIGHT
WHICH THE 12Z NAM SHOWED WELL ENOUGH IS NOT SIGNIFICANT IN THE
GLOBAL MODELS.



&&

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

&&

$$

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