Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 160349
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
850 PM PDT WED OCT 15 2014

.SYNOPSIS...MOIST SOUTHWEST FLOW ALOFT WILL ALLOW SCATTERED SHOWERS
TO CONTINUE OVER WESTERN WASHINGTON TONIGHT. A WEAK UPPER LEVEL
RIDGE WILL MOVE BRIEFLY OVER THE AREA THURSDAY FOR PARTLY SUNNY AND
DRY WEATHER. A SLOW MOVING FRONTAL SYSTEM WILL BRING RAIN TO WESTERN
WASHINGTON THURSDAY NIGHT THROUGH FRIDAY NIGHT. A FEW SHOWERS WILL
PERSIST ON SATURDAY AS THE FRONT SLOWLY DISSIPATES. ANOTHER RIDGE
WILL MOVE OVER THE AREA LATE SATURDAY AND SUNDAY. A FRONTAL SYSTEM
WILL BRING RAIN SUNDAY NIGHT AND MONDAY.

&&

.SHORT TERM...AN UPPER LEVEL SHORTWAVE TROUGH OVER W WA EARLY THIS
EVENING WILL MOVE OVER E WA BY 06Z/11 PM ALLOWING SHOWER ACTIVITY TO
DECREASE. MOIST SW FLOW ALOFT OVER THE REGION WILL BRING ANOTHER
WEAK UPPER LEVEL SHORTWAVE TROUGH OFFSHORE NEAR 130W TO THE COAST
AROUND 12Z/5 AM THURSDAY MORNING. IR IMAGERY SHOWS A MOIST BUT
DISORGANIZED LOOKING CLOUD MASS OFFSHORE ASSOCIATED WITH THE
SHORTWAVE. I WOULD EXPECT SOME SHOWERS WITH THIS SHORTWAVE ON
THURSDAY...BUT EXCEPT FOR SOME SHOWERS ON THE COAST IN THE MORNING
ALL THE MODELS KEEP THE INTERIOR DRY. THIS IS PROBABLY BECAUSE THE
NEXT FRONTAL SYSTEM IS BEGINNING TO DEEPEN OFFSHORE ALONG
140W...ALLOWING A WEAK UPPER LEVEL RIDGE TO BUILD DOWNSTREAM OVER
THE PACIFIC NORTHWEST. A SURFACE RIDGE CENTERED OVER E WA ALSO
FORMS. WINDS WILL WEAKEN AND THERE SHOULD BE ENOUGH CLEARING FOR
PARTLY SUNNY SKIES AND NEAR NORMAL TEMPERATURES.

MODELS ARE IN FAIRLY GOOD AGREEMENT WITH THE FRONTAL SYSTEM
DEVELOPING OFFSHORE ALONG 140W. THE WHOLE SYSTEM WILL TRANSITION
ONLY SLOWLY EAST...ALLOWING RAIN TO FALL THROUGH FRIDAY NIGHT. THE
INITIAL WARM ADVECTION RAIN WILL SPREAD OVER THE COAST THURSDAY
NIGHT WITH PROBABLY NOT MUCH REACHING INLAND AREAS. THE SYSTEM WILL
MOVE FAR ENOUGH EAST ON FRIDAY FOR LIGHT RAIN AT TIMES OVER THE
INTERIOR. THE FRONT WILL STILL BE OFFSHORE ALONG ROUGHLY 126W 00Z
SAT/5 PM FRIDAY AFTERNOON. THE BEST RAIN OVER THE INTERIOR WILL BE
FRIDAY EVENING WITH THE FRONT FINALLY REACHING THE COAST AROUND
06Z/11 PM. AT THIS POINT THE SYSTEM WILL BE WEAKENING RAPIDLY WITH
THE UPPER LEVEL TROUGH HEADED FOR E WA WHILE THE SURFACE FRONT FALLS
APART OVER WESTERN WA.

WHILE THE SYSTEM IS OFFSHORE ON FRIDAY THE SYSTEM WILL BE FAIRLY
STRONG WITH HEALTHY PRESSURE GRADIENTS. THIS WILL ALLOW VERY WINDY
CONDITIONS TO DEVELOP ALONG THE COAST THURSDAY NIGHT AND FRIDAY WITH
ISOLATED GUSTS TO 45-50 MPH. OVER THE INTERIOR...FRIDAY AND FRIDAY
EVENING WILL BE THE MOST WINDY...WITH GUSTS TO 45 MPH IN SOME SPOTS
OVER THE N INTERIOR THAT ARE PRONE TO S-SE WINDS LIKE WHATCOM COUNTY
AND SAN JUAN COUNTY. WINDS IN THESE SPOTS ARE IN THE BORDERLINE WIND
ADVISORY RANGE AND AN ADVISORY WILL BE CONSIDERED AS THE EVENT DRAWS
CLOSER.

WITH THE FRONT DISSIPATING OVER THE REGION SATURDAY THE AIR MASS
WILL REMAIN QUITE MOIST...SUPPORTING A CHANCE OF SHOWERS. KAM

.LONG TERM...PREVIOUS DISCUSSION FROM THE 245 PM AFD...DRY WEATHER
IS A GOOD BET SATURDAY NIGHT AND SUNDAY...ALTHOUGH THERE IS A CHANCE
OF RAIN IN THE FORECAST ON THE COAST SUNDAY. THE NEXT FRONT MOVES
THROUGH THE AREA SUNDAY NIGHT AND MONDAY...FOLLOWED BY SHOWERS AND A
BREAK TUESDAY...AND THEN A STRONGER FRONT NEXT WEDNESDAY.

&&

.AVIATION...LIGHT TO MODERATE WESTERLY FLOW TONIGHT BETWEEN SYSTEMS.
A TROUGH WILL APPROACH THE PAC NW THURSDAY WITH MODERATE SLY FLOW
DEVELOPING. GENERALLY MOIST TONIGHT WITH SOME DRYING IN THE LOWER
LEVELS ON THURSDAY. UNSTABLE ATMOSPHERE TONIGHT WITH ISOLATED
THUNDERSTORMS...MAINLY NEAR THE COAST. BECOMING MOSTLY STABLE ON
THURSDAY. MOSTLY VFR CIGS. PATCHY MVFR LATER TONIGHT AND THURSDAY
MORNING...ESPECIALLY ASSOCIATED WITH SHOWERS.

KSEA...CIGS GENERALLY 3-5K FT THROUGH THURSDAY MORNING...THEN ABOVE
5K FT THURSDAY AFTERNOON. ISOLATED SHOWERS POSSIBLE BUT ONLY A 10
PERCENT CHANCE OF AN ISOLATED THUNDERSTORM TONIGHT. DTM

&&

.MARINE...A STRONG PACIFIC FRONTAL SYSTEM WILL AFFECT THE REGION
THURSDAY THROUGH FRIDAY. PRESSURE GRADIENTS WILL TIGHTEN OVER THE
THE COASTAL WATERS TONIGHT WITH SMALL CRAFT WINDS DEVELOPING. MODELS
SHOW GALES OVER THE COASTAL WATERS LATE THURSDAY INTO FRIDAY WITH
COMBINED SEAS OF 14 TO 20 FEET. GALES MAY ALSO OCCUR AT THE
ENTRANCES TO THE STRAIT OF JUAN DE FUCA. A GALE WATCH REMAINS IN
EFFECT FOR THE COAST FOR MIDDAY THURSDAY THROUGH FRIDAY AFTERNOON.
THIS SYSTEM WILL EXIT FRIDAY NIGHT WITH HIGH PRES MOVING INLAND ON
SATURDAY. ANOTHER STRONG FRONT WILL APPROACH WASHINGTON SUNDAY.
DTM

&&

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

PZ...SMALL CRAFT ADVISORY COAST...EAST ENTRANCE...ADMIRALTY INLET...
     PUGET SOUND AND HOOD CANAL.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.
     GALE WATCH COAST.

&&

$$

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