Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 152144
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
245 PM PDT TUE APR 15 2014

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

&&

.SHORT TERM...A WARM FRONT WILL STALL OVER WESTERN WASHINGTON...
BRINGING RAIN AT TIMES TONIGHT THROUGH WEDNESDAY NIGHT. A COLD FRONT
WILL MOVE THROUGH THE AREA ON THURSDAY WITH RAIN CHANGING TO SHOWERS
LATE IN THE DAY. THIS WILL BE FOLLOWED BY A MAINLY DRY PERIOD
THURSDAY NIGHT AND FRIDAY AS WEAK HIGH PRESSURE BUILDS OVER THE
PACIFIC NORTHWEST. A PUGET SOUND CONVERGENCE ZONE LOOKS LIKELY
THURSDAY NIGHT BEHIND THE COLD FRONT.

THE TONIGHT THROUGH THURSDAY PERIOD IS LOOKING PRETTY WET. STEADY
RAIN FOR 48 HOURS STRAIGHT HOURS IS PRETTY UNLIKELY AND THERE WILL
CERTAINLY BE SOME BREAKS IN THE RAIN OVER THE NEXT COUPLE OF DAYS
BUT THE GENERAL IDEA IS RAIN AT TIMES THROUGH THURSDAY. HEAVY RAIN
IS NOT EXPECTED...BUT THE CUMULATIVE RAINS OVER THE NEXT 48 HOURS
ARE EXPECTED TO BE 0.75 TO 1.50 INCHES OVER THE INTERIOR LOWLANDS...
1-2 INCHES AT THE COAST...AND 1.5 TO 3.0 INCHES FOR THE MOUNTAINS.
SCHNEIDER

.LONG TERM...A FRONTAL SYSTEM WILL REACH THE AREA LATER IN THE DAY
SATURDAY WITH RAIN CHANGING TO SHOWERS SATURDAY NIGHT. SUNDAY WILL
PROBABLY BE A MAINLY DRY DAY IN BETWEEN WEATHER SYSTEMS. A FAIRLY
WEAK FRONT IS FORECAST TO BRING A LITTLE MORE RAIN MONDAY. AFTER
THAT...MODELS DIVERGE SIGNIFICANTLY. THE GFS BUILD AN UPPER RIDGE
OVER THE AREA ON TUESDAY FOR A DRY DAY. THE ECMWF DROPS A COLD UPPER
TROUGH OVERHEAD WITH A LEAST SOME SHOWERS. SCHNEIDER

&&

.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 HALF FOOT
TONIGHT...ANOTHER FOOT OR SO ON WEDNESDAY...AND THEN ABOUT TWO FEET
ON THURSDAY. THE RIVER AND POOL LEVELS WILL BEGIN FALLING LATER
THURSDAY NIGHT AND CONTINUE FALLING FRIDAY AS HIGH PRESSURE MOVES
OVER THE AREA.

TOTAL RAINFALL FOR THE SLIDE AREA TONIGHT THROUGH THURSDAY WILL BE
ON THE ORDER OF TWO INCHES. A QUARTER TO HALF INCH IS EXPECTED
TONIGHT...ANOTHER THREE QUARTERS OF AN INCH OR SO WEDNESDAY...AND
THEN ABOUT AN INCH ON THURSDAY.

ADDITIONAL FRONTS WILL AFFECT THE SLIDE AREA LATER SATURDAY AND
MONDAY. THESE SYSTEMS ARE NOT EXPECTED TO BE ESPECIALLY WET OR
HYDROLOGICALLY SIGNIFICANT BUT THEY WILL KEEP CONDITIONS WET.
SCHNEIDER

&&

.AVIATION...MODERATE NORTHWEST FLOW ALOFT TONIGHT AND WEDNESDAY. A
WARM FRONT WILL MOVE INTO THE AREA TONIGHT. AIR MASS IS MOIST AND
STABLE WITH INCREASING CLOUDS. RAIN ON THE COAST AT 22Z WILL SPREAD
INLAND BY 02Z. AT THE SURFACE HIGH PRESSURE OFFSHORE WILL MOVE OVER
THE AREA WEDNESDAY.

GENERALLY VFR CEILINGS WILL FALL TO MVFR 2-3K FT BY 06Z. VISIBILITY
OCCASIONALLY 3-5SM IN RAIN. AFTER 15Z WEDNESDAY SOME CEILINGS WILL
FALL BELOW 2K FT.

KSEA...SOUTHERLY WIND 8-12 KT TONIGHT AND WEDNESDAY. RAIN TONIGHT
WITH MVFR CEILINGS DOMINANT. CHB

&&

.MARINE...A WARM FRONT WILL MOVE INTO THE AREA TONIGHT. THIS SEEMS
LIKELY TO BRING SMALL CRAFT ADVISORY STRENGTH WINDS TO THE COAST AND
WEST ENTRANCE AND HAVE HOISTED ADVISORIES FOR THOSE ZONES THROUGH
THIS EVENING. WINDS ARE FORECAST TO BE LESS THAN 20 KT ELSEWHERE BUT
AS WITH ANY FRONT THE SOUTHERLIES COULD SURPRISE AND GO ABOVE 20 KT
SOME TIME TONIGHT.

HIGH PRES AND LIGHTER FLOW ON WEDNESDAY. A STRONGER FRONT WILL BRING
SMALL CRAFT ADVISORY WINDS TO MOST OF THE WATERS ON THURSDAY. LATEST
GFS INDICATES GALE FORCE WESTERLIES ARE POSSIBLE IN THE STRAIT
THURSDAY AFTERNOON AND EVENING BUT LATEST MM5 4KM RUNS SUGGEST LOWER
WINDS. WINDS EASE FRIDAY AS HIGH PRES BUILDS OVER THE AREA. CHB

&&

.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 COAST AND WEST ENTRANCE.

&&

$$

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