Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 151022
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
330 AM PDT TUE APR 15 2014

.SYNOPSIS...A WARM FRONT WILL MOVE INLAND TODAY THEN STALL OVER THE
REGION ON WEDNESDAY FOR RAIN AT TIMES. A COLD FRONT WILL THEN CROSS
WESTERN WASHINGTON ON THURSDAY. DRIER WEATHER IS FORECAST ON FRIDAY
WITH WEAK HIGH PRESSURE OVERHEAD. THE NEXT FRONT WILL ARRIVE ON
SATURDAY.

&&

.SHORT TERM...RADAR SHOWS A FEW LIGHT SHOWERS ACROSS THE AREA THIS
MORNING. BUT RAIN WILL INCREASE IN COVERAGE THIS AFTERNOON AND
EVENING AS A WARM FRONT MOVES IN. IT LOOKS LIKE THIS FRONT WILL
STALL OVER THE REGION THROUGH WEDNESDAY FOR MORE CLOUDY SKIES AND
LIGHT RAIN AT TIMES. A COLD FRONT WILL THEN SWEEP THROUGH THE AREA
ON THURSDAY FOR ANOTHER WET PERIOD OF WEATHER. EXPECT SCATTERED
SHOWERS THURSDAY NIGHT WITH POST-FRONTAL ONSHORE FLOW. A PUGET SOUND
CONVERGENCE ZONE MAY FORM OVER THE CENTRAL SOUND. THE PSCZ MAY
LINGER INTO FRIDAY MORNING...OTHERWISE FRIDAY IS LOOKING DRIER WITH
WEAK HIGH PRES OVER THE REGION. 33

.LONG TERM...OUR NEXT FRONT WILL ARRIVE SATURDAY AFTERNOON AS A COLD
FRONT MOVES INLAND. THE ECMWF IS STRONGER WITH THIS SYSTEM COMPARED
TO THE GFS. HOWEVER BOTH MODELS SHOW SIMILAR TIMING WITH THIS FRONT.
WILL KEEP A BLEND OF THE MODELS FOR NOW. AFTER THAT...THE MODELS DO
NOT AGREE ON THE TIMING OF THE NEXT SYSTEM. BOTH MODELS SHOW AN
UPPER LOW SPINNING OVER THE NE PAC...BUT THEY DIFFER ON WHEN THIS
SYSTEM WILL IMPACT WESTERN WA. CONFIDENCE IS LOW AND LITTLE CHANGES
WERE MADE FROM THE PREVIOUS FORECAST. 33

&&

.HYDROLOGY...RIVER FLOODING IS UNLIKELY FOR THE NEXT 7 DAYS.

THE EXCEPTION IS THE NORTH FORK OF THE STILLAGUAMISH RIVER EAST OF
THE SR 530 LANDSLIDE NEAR OSO WHERE A FLOOD WARNING REMAINS IN
EFFECT UNTIL FURTHER NOTICE. FLOODING CONTINUES FOR THIS RIVER AS A
RESULT OF WATER POOLED BEHIND THE DEBRIS DAM THAT PARTIALLY BLOCKS
THE RIVER.

THE NORTH FORK OF THE STILLAGUAMISH NEAR ARLINGTON AND THE POOL
UPSTREAM OF THE SR 530 SLIDE ARE FORECAST TO RISE ABOUT A FOOT
TONIGHT AS A WEAK FRONT BRINGS RAIN AT TIMES.

AT THIS TIME...THE MOST SIGNIFICANT SYSTEMS ARE EXPECTED
TONIGHT...GIVING ABOUT A QUARTER OF AN INCH OF RAIN TO THE SLIDE
AREA...AND ON THURSDAY...GIVING AN INCH OF RAIN TO THE SLIDE AREA AS
A COLD FRONT MOVES IN.

LIGHT SHOWERS AT OTHER TIMES THIS WEEK ARE NOT EXPECTED TO GIVE
HYDROLOGICALLY SIGNIFICANT RAINFALL TO THE SLIDE AREA...BUT WILL
KEEP CONDITIONS WET.

&&

.AVIATION...MODERATE W-NW FLOW ALOFT TODAY. A WARM FRONT WILL LIFT
NWD ACROSS THE AREA TONIGHT WITH MODERATE SW FLOW ALOFT. HIGH
PRESSURE OFFSHORE MOVES OVER THE REGION ON WED. SOMEWHAT MOIST AT
ALL LEVELS TODAY...THEN MOIST TONIGHT AND WED. STABLE ATMOSPHERE.
VARIABLE CIGS TODAY BUT GENERALLY VFR ABOVE 3K FT. CIGS LOWERING TO
2K FT AT TIMES WITH ANY PRECIPITATION. MVFR CIGS WILL DOMINATE
TONIGHT AS RAIN INCREASES.

KSEA...S WIND 6-12 KT. CIGS 2500-3500 FT W/ SPOTTY LIGHT RAIN TODAY.
RAIN TONIGHT WITH MVFR CIGS DOMINATE.

&&

.MARINE...MODERATE ONSHORE FLOW TODAY WILL SLOWLY WEAKEN. A WARM
FRONT WILL LIFT ACROSS THE WATERS TONIGHT. THIS COULD PRODUCE SMALL
CRAFT WINDS OVER THE COASTAL WATERS AND POSSIBLY SOME INTERIOR
WATERS. HIGH PRESSURE AND LIGHTER FLOW WED. A STRONGER FRONT WILL
BRING SMALL CRAFT WINDS TO MOST OF THE WATERS ON THU.

&&

.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...SMALL CRAFT ADVISORY CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA.

&&

$$

WWW.WEATHER.GOV/SEATTLE

YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML





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