Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 180420
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
920 PM PDT THU APR 17 2014

.SYNOPSIS...SHOWERS WILL DECREASE TONIGHT AS A FRONT MOVES INLAND.
DRIER WEATHER IS FORECAST ON FRIDAY WITH WEAK HIGH PRESSURE
OVERHEAD. A SECOND FRONT WILL ARRIVE LATER SATURDAY. A BROAD UPPER
LEVEL TROUGH WILL BRING SHOWERY WEATHER EARLY NEXT WEEK.

&&

.SHORT TERM...STRONG ONSHORE FLOW EASE OVERNIGHT AND SHOWERS WILL
TAPER OFF...MAINLY CONFINED TO THE MOUNTAINS AND THE PUGET SOUND
CONVERGENCE ZONE. A WEAK UPPER RIDGE WILL BUILD OVER THE AREA ON
FRIDAY FOR A MOSTLY DRY DAY. SKIES ARE EXPECTED TO BECOME PARTLY
SUNNY LATER FRIDAY AS THE LOW LEVELS DRY. A SECOND FRONT WILL BRING
RAIN LATER SATURDAY. MODELS HAVE BEEN PRETTY CONSISTENT WITH THE
IDEA OF RAIN REACHING THE COAST AROUND MID-MORNING AND SPREADING
INLAND IN THE AFTERNOON. SUNDAY WILL PROBABLY BE A MAINLY DRY DAY IN
BETWEEN WEATHER SYSTEMS. A THIRD FRONT WILL BE APPROACHING FROM THE
WEST ON SUNDAY. MODELS HAVE NOT BEEN CONSISTENT WITH WHAT THIS FRONT
WILL DO. THE BEST GUESS FOR NOW IS THE FRONT WILL SLOW DOWN AND
STALL NEAR THE COAST ON SUNDAY. THE COAST WILL PROBABLY SEE SOME
RAIN FROM THIS SYSTEM SUNDAY BUT THERE IS A GOOD CHANCE THE INTERIOR
WILL STAY DRY.

.LONG TERM...AN UPPER TROUGH OVER THE EASTERN PACIFIC WILL MOVE
TOWARD THE PACIFIC NORTHWEST MONDAY WITH INCREASINGLY MOIST AND
UNSTABLE SOUTHERLY FLOW ALOFT. THIS PATTERN COULD BE FAVORABLE FOR
AFTERNOON AND EVENING THUNDERSTORMS...MAINLY OVER THE CASCADES.

THE UPPER TROUGH WILL SHIFT OVER WESTERN WASHINGTON TUESDAY...THEN
SAG SOUTH OF THE AREA WEDNESDAY WITH WEAK HIGH PRESSURE BUILDING
OVERHEAD. TUESDAY WILL PROBABLY BE A FAIRLY SHOWERY DAY...WITH LESS
SHOWERS ON WEDNESDAY AS THE UPPER TROUGH PULLS AWAY. A FRONT COULD
REACH THE AREA ON THURSDAY BUT CONFIDENCE IN THIS IS PRETTY LOW FOR
NOW. 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 IS FORECAST TO
CREST JUST UNDER 9 FEET TONIGHT. THE RIVER LEVEL WILL THEN
BEGIN FALLING LATER TONIGHT AND CONTINUE FALLING ON FRIDAY AS HIGH
PRESSURE MOVES OVER THE AREA. A FRONT WILL BRING ANOTHER BATCH OF
RAIN SATURDAY AFTERNOON AND EVENING. THIS IS EXPECTED TO CAUSE THE
RIVER TO RISE ABOUT A FOOT SATURDAY NIGHT. THE RIVER WILL BEGIN
FALLING AGAIN SUNDAY AND CONTINUE TO FALL EARLY NEXT WEEK AS DRIER
WEATHER PREVAILS.

&&

.AVIATION...COLD FRONT AND UPPER LEVEL TROUGH MOVED EAST OF THE AREA
TONIGHT. STRONG NORTHWESTERLY FLOW ALOFT. PUGET SOUND CONVERGENCE
ZONE BETWEEN KPAE AND KBFI. STRONG FLOW ALOFT WILL PUSH CONVERGENCE
ZONE INTO CASCADES OVERNIGHT. CONVERGENCE ZONE COULD GET AS FAR
SOUTH AS KBFI. UPPER LEVEL RIDGE BUILDING OFFSHORE FRIDAY WITH
NORTHWESTERLY FLOW ALOFT CONTINUING. LOW LEVEL ONSHORE FLOW
BECOMING LIGHT FRIDAY AFTERNOON.

CEILINGS IN THE 3500 TO 5000 FOOT RANGE OVERNIGHT EXCEPT IN THE
VICINITY OF THE CONVERGENCE ZONES WHERE CEILINGS WILL BE BELOW 1000
FEET WITH VISIBILITIES 3-5SM IN SHOWERS. CEILINGS AOA 5000 FEET
LATER FRIDAY MORNING INTO FRIDAY AFTERNOON.

KSEA...CEILINGS AROUND 2000 FEET UNTIL THE EARLY MORNING HOURS WITH
CEILINGS IMPROVING TO 3500 TO 5000 FEET FOR FRIDAY MORNING.
CEILINGS CONTINUING TO IMPROVE LATE FRIDAY MORNING INTO FRIDAY
AFTERNOON. SOUTHWEST WIND 10-15 KNOTS WITH GUSTS 20-25 KNOTS EASING
BY 12Z. WINDS BECOMING LIGHT FRIDAY AFTERNOON. FELTON

&&

.MARINE...SURFACE HIGH PRESSURE BUILDING OVER THE WATERS TONIGHT IN
THE WAKE OF THE THURSDAY AFTERNOON COLD FRONT. GALE FORCE WINDS IN
THE CENTRAL AND EASTERN STRAIT WITH SMALL CRAFT ADVISORY WINDS OVER
THE REMAINDER OF THE WATERS. WINDS EASING FRIDAY MORNING AS SURFACE
HIGH PRESSURE BUILDS INLAND. EXPECT A STRONG COLD FRONT TO IMPACT
THE REGION ON SATURDAY...FOLLOWED BY A WEAKER SYSTEM LATE SUNDAY.

A LARGE SWELL TRAIN BEHIND THE COLD FRONT ON SATURDAY WILL ARRIVE
ALONG THE WASHINGTON COAST SATURDAY NIGHT AND CONTINUE INTO SUNDAY.
SWELL AS HIGH AS 18 FEET ARE POSSIBLE. FELTON

&&

.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 WARNING IN EFFECT UNTIL 5 AM FRI FOR THE CENTRAL AND
     EASTERN STRAIT OF JUAN DE FUCA.

     SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE REMAINING WATERS.

&&

$$

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