Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 181017
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
330 AM PDT FRI APR 18 2014

.SYNOPSIS...SHOWERS ASSOCIATED WITH A PUGET SOUND CONVERGENCE ZONE
OVER KING COUNTY WILL DIMINISH THIS MORNING. OTHERWISE DRIER
WEATHER IS FORECAST TODAY WITH WEAK HIGH PRESSURE OVERHEAD. THE NEXT
COLD FRONT WILL ARRIVE ON SATURDAY. A BROAD UPPER LEVEL TROUGH
WILL BRING SHOWERY WEATHER EARLY NEXT WEEK.

&&

.SHORT TERM...SHOWERS ARE MAINLY TIED TO THE PUGET SOUND CONVERGENCE
ZONE OVER KING COUNTY EARLY THIS MORNING. THE PSCZ SHOULD DIMINISH
LATER THIS MORNING AS ONSHORE FLOW WEAKENS AND A WEAK UPPER LEVEL
RIDGE MOVES INLAND. WE SHOULD SEE PARTLY SUNNY SKIES TODAY WITH
HIGHS IN THE MID 50S TO LOWER 60S. DRY WEATHER WILL CONTINUE TONIGHT
WITH LOWS DROPPING INTO THE UPPER 30S TO MID 40S.

A COLD FRONT WILL REACH THE COAST SATURDAY MORNING THEN PUSH
INTO THE INTERIOR DURING THE AFTERNOON. THE TRAILING UPPER LEVEL
TROUGH WILL MAINTAIN SHOWERS ACROSS WESTERN WA SAT NIGHT.

ANOTHER COLD FRONT WILL REACH THE COAST ON SUNDAY THEN WEAKEN AS
PIVOTS AND BECOMES NORTH-SOUTH ORIENTATED OFFSHORE. MODELS KEEPS THE
INTERIOR MAINLY DRY.

AN UPPER LEVEL LOW OVER THE NE PAC WILL START TO SHIFT INLAND ON
MONDAY WHICH WILL RESULT IN ISOLATED TO SCATTERED SHOWERS ACROSS THE
REGION. 33

.LONG TERM...THE AIR MASS WILL REMAIN COOL AND UNSTABLE ON TUE AS AN
UPPER LEVEL LOW CROSSES THE PAC NW. MODELS CONTINUE TO SHOW A FEW
SHOWERS ACROSS WESTERN WA OVER THIS PERIOD. A WEAK RIDGE MAY BRING
DRIER WEATHER NEXT WEDNESDAY...BUT THEN ANOTHER FRONTAL SYSTEM IS
SLATED TO ARRIVE WED NIGHT OR THURSDAY. TIMING OF THIS NEXT SYSTEM
IS STILL UNCLEAR IN THE MODELS. MODELS ARE SHOWING ANOTHER
COOL/SHOWERY WEATHER PATTERN NEXT WEEKEND AS ANOTHER UPPER LEVEL
TROUGH FORMS OVER THE PAC NW. 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 CRESTED AT 7.4
FEET EARLY THIS MORNING AND IS NOW FALLING. THE RIVER LEVEL WILL
CONTINUE FALLING TODAY 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...WEAK UPPER LEVEL RIDGE OFFSHORE MOVING TOWARDS THE COAST
THIS AFTERNOON AND INLAND THIS EVENING. NORTHWESTERLY FLOW ALOFT
BECOMING SOUTHWESTERLY SATURDAY MORNING. CONVERGENCE ZONE NORTH AND
EAST OF KBFI EARLY THIS MORNING WILL MOVE INTO THE CASCADES BY 15Z.

CEILINGS NEAR AND JUST SOUTH OF THE CONVERGENCE ZONE NEAR 2000 FEET
EARLY THIS MORNING. AWAY FROM THE CONVERGENCE ZONE CEILINGS
GENERALLY IN THE 3500 TO 5000 FOOT RANGE. CEILINGS WILL IMPROVE THIS
MORNING WITH CLOUDS SCATTERING OUT THIS AFTERNOON WITH AN UPPER
LEVEL RIDGE APPROACHING THE COAST. MID LEVEL CLOUD DECK OUT AHEAD
OF THE NEXT SYSTEM ARRIVING SATURDAY MORNING.

KSEA...CEILINGS AROUND 2000 FEET EARLY THIS MORNING WITH CEILINGS
IMPROVING TO 3500 TO 5000 FEET DURING THE MORNING HOURS. CLOUDS
SCATTERING OUT LATE MORNING AND AFTERNOON HOURS. SOUTHWEST WIND 6 TO
10 KNOTS BECOMING LIGHT MIDDAY. WINDS GOING NORTHWESTERLY 4 TO 8
KNOTS LATE AFTERNOON AND EVENING HOURS. FELTON

&&

.MARINE...SURFACE HIGH PRESSURE OVER THE WATERS TODAY WILL SHIFT
EAST TONIGHT. A STRONG COLD FRONT WILL MOVE THROUGH THE WATERS ON
SATURDAY WITH SMALL CRAFT ADVISORY WINDS EXPECTED OVER ALL OF THE
WATERS. HIGH PRESSURE WILL REBUILD ON SUNDAY. A WEAKER SYSTEM WILL
ARRIVE LATER MONDAY OR MONDAY NIGHT.

A LARGE SWELL TRAIN BEHIND THE COLD FRONT ON SATURDAY WILL ARRIVE
ALONG THE WASHINGTON COAST SATURDAY NIGHT AND CONTINUE INTO SUNDAY.
SWELLS IN THE 16 TO 19 FOOT RANGE ARE EXPECTED. THIS IS A RAZOR CLAM
DIG WEEKEND FOR TWIN HARBORS...COPALIS AND MOCROCKS BEACHES. 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...SMALL CRAFT ADVISORY CENTRAL AND EASTERN STRAIT THIS MORNING.
     SMALL CRAFT ADVISORY COASTAL WATERS AND WEST ENTRANCE TO THE
     STRAIT FOR HAZARDOUS SEAS THIS MORNING.

&&

$$

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