Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 132137
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
240 PM PDT SUN APR 13 2014

.SYNOPSIS...A STRONG UPPER LEVEL RIDGE AND OFFSHORE SURFACE FLOW
WILL KEEP WESTERN WASHINGTON DRY THROUGH MONDAY. CHANGES WILL OCCUR
MONDAY NIGHT AS A MARINE PUSH BRING CLOUDS AND A CHANCE OF SHOWERS.
A COUPLE OF WEAK WEATHER SYSTEMS WILL PROBABLY BRING RAIN TUESDAY
AND AGAIN THURSDAY NIGHT...WITH SCATTERED SHOWERS DURING THE
INTERVENING PERIOD.

&&

.SHORT TERM...SKIES HAVE BEEN SUNNY ALL DAY AND HIGHS WILL BE IN THE
MID 60S TO LOW 70S. SKIES WILL REMAIN CLEAR TONIGHT WITH LOWS MAINLY
IN THE 40S BUT ALSO SOME UPPER 30S IN SHELTERED LOCATIONS.

THE UPPER RIDGE WILL MOVE EAST TONIGHT AND FLOW ALOFT ON MONDAY WILL
BE SOUTHWESTERLY. STRONG ONSHORE SURFACE FLOW WILL DEVELOP IN THE
AFTERNOON. BY AFTERNOON IT WILL BE CLOUDY ON THE COAST THOUGH STILL
SUNNY INLAND. HIGH TEMPERATURES MONDAY WILL BE 5-10 DEGREES LOWER
THAN TODAY WITH THE MOST NOTICEABLE DROPS ON THE COAST. LIGHT RAIN
WILL DEVELOP OVER COASTAL AND MOUNTAIN AREAS MONDAY NIGHT AND BECOME
MORE WIDESPREAD ON TUESDAY. HAVE KEPT POPS LIKELY ON THE COAST AND
IN THE MOUNTAINS TUESDAY MORNING THEN SPREAD THE LIKELY POPS TO
EVERYWHERE TUESDAY AFTERNOON. HIGHS ON TUESDAY WILL BE IN THE MID
50S TO LOW 60S UNDER CLOUDY SKIES.

THE NAM AND GFS ARE FAIRLY DRY WEDNESDAY AS UPPER AND SURFACE RIDGES
BUILD. THE EURO KEEPS THINGS WET IN A MORE PROGRESSIVE AND MOIST
NORTHWESTERLY FLOW PATTERN. HAVE LOWERED POPS WEDNESDAY TO MORE OF A
SCATTERED SHOWER REGIME AND INTRODUCED PARTLY SUNNY WORDING. IN
DEFERENCE TO THE EURO HAVE NOT ELIMINATED POPS COMPLETELY. HIGHS
WILL REBOUND A FEW DEGREES ON WEDNESDAY IF THE SUN APPEARS. BURKE

.LONG TERM...NEXT SYSTEM IS DUE ABOUT THURSDAY NIGHT AND IN THIS THE
GFS AND EURO MORE OR LESS AGREE. HAVE LIKELY POPS THURSDAY NIGHT
EVERYWHERE. MODEL AGREEMENT CONTINUES ON FRIDAY WITH BOTH MODELS
SHOWING SCATTERED SHOWERS AND ALSO ON SATURDAY WITH BOTH MODELS
MOSTLY DRY. HAVE NOT CUT POPS TO ZERO ANY PERIOD AS MODELS HAVE BEEN
CHANGEABLE AND THIS IS CERTAINLY THE TIME OF YEAR WHEN THE EXTENDED
FORECAST IS MOST CHANCY. ANOTHER SYSTEM IS IN THE MODELS SUNDAY OR
SUNDAY NIGHT. BURKE

&&

.HYDROLOGY...RIVER FLOODING IS UNLIKELY ON AREA RIVERS...EXCEPT THE
NORTH FORK OF THE STILLAGUAMISH EAST OF OSO...FOR THE NEXT 7 DAYS.

A FLOOD WARNING REMAINS IN EFFECT UNTIL FURTHER NOTICE FOR THE
NORTH FORK OF THE STILLAGUAMISH RIVER IN SNOHOMISH COUNTY JUST
UPSTREAM OF THE SR 530 LANDSLIDE. FLOODING CONTINUES AS A RESULT
OF WATER POOLED BEHIND THE DEBRIS DAM THAT PARTIALLY BLOCKS THE
RIVER.

THE NORTH FORK STILLAGUAMISH NEAR ARLINGTON AND THE POOL UPSTREAM OF
THE SR 530 SLIDE WILL CONTINUE FALLING THROUGH TUESDAY MORNING AS A
STRONG UPPER LEVEL RIDGE KEEPS THE WEATHER DRY. A SHIFT TO A WETTER
WESTERLY FLOW PATTERN WILL OCCUR BEGINNING TUESDAY.

THE RIVER AND UPSTREAM POOL ARE FORECAST TO RISE ABOUT A FOOT
TUESDAY AFTERNOON AND EVENING...THEN RESUME A SLOW DOWNWARD TREND.
AT THIS TIME...THE MOST SIGNIFICANT SYSTEMS ARE EXPECTED LATE MONDAY
NIGHT THROUGH TUESDAY MORNING...GIVING AROUND A HALF INCH OF RAIN TO
THE SLIDE AREA...AND ON THURSDAY NIGHT...GIVING ANOTHER QUARTER TO
HALF AN INCH OF RAIN TO THE SLIDE AREA. LIGHT SHOWERS AT OTHER TIMES
WILL NOT GIVE HYDROLOGICALLY SIGNIFICANT RAINFALL TO THE SLIDE
AREA...BUT WILL KEEP CONDITIONS WET. BURKE

&&

.AVIATION...DRY STABLE AIR AND LIGHT OFFSHORE FLOW WILL GIVE WAY TO
ONSHORE FLOW AND A COLD FRONT LATER ON MONDAY. THE STRATUS THAT IS
OFFSHORE BEYOND 130W SHOULD NEAR THE COAST ON MONDAY AND THEN CLOUDY
SKIES WILL DEVELOP OVER WRN WA MONDAY EVENING AS A COLD FRONT
REACHES THE AREA.

KSEA...CLEAR WITH LIGHT NY WIND BECOMING LIGHT AND VARIABLE TONIGHT
AND THEN LIGHT SLY WIND MONDAY...INCREASING MONDAY EVENING AS A
FRONT NEARS THE AREA.

&&

.MARINE...THERMALLY INDUCED LOW PRESSURE ALONG THE NORTH CALIF COAST
EXTENDS NORTH TOWARD VANCOUVER ISLAND...BUT GRADIENTS ARE PRETTY
LIGHT AROUND WRN WA. ONSHORE FLOW WILL DEVELOP MONDAY AND INCREASE
MONDAY EVENING AS A COLD FRONT NEARS THE AREA. WLY GALES ARE
POSSIBLE IN THE STRAIT MONDAY NIGHT. ONSHORE/WLY FLOW TUESDAY WILL
BECOME LIGHT WED. A WEAKER FRONT IS POSSIBLE LATE IN THE WEEK.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WARNING REMAINS IN EFFECT FOR THE NORTH FORK OF THE
      STILLAGUAMISH RIVER EAST OF THE SR 530 LANDSLIDE.

PZ...GALE WATCH MONDAY NIGHT CENTRAL STRAIT OF JUAN DE FUCA AND EAST
      ENTRANCE TO THE STRAIT.

&&

$$

WWW.WEATHER.GOV/SEATTLE

YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT
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