Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 281648
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
948 AM PDT THU APR 28 2016

.SYNOPSIS...WEAK UPPER LEVEL RIDGE MOVING ACROSS WESTERN
WASHINGTON TODAY. SPOTTY LIGHT SHOWERS COULD DEVELOP OVER THE
MOUNTAINS LATE. A FRONT AND ITS UPPER TROUGH WILL BRING SHOWERS LATE
TONIGHT AND FRIDAY. A STRONG UPPER RIDGE WILL BRING DRY WARMER
WEATHER SATURDAY THROUGH MONDAY. A CHANCE OF PRECIPITATION WILL
RETURN TUESDAY THROUGH WEDNESDAY.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS SC DECK OVER WESTERN
WASHINGTON BETWEEN THE PUGET SOUND AND THE CASCADES. SOME SC ALSO
ALONG THE NORTH COAST WITH A BIG CLEAR AREA FROM THE CENTRAL STRAIT
OF JUAN DE FUCA THROUGH THE OLYMPICS DOWN TO THE LOWER CHEHALIS
VALLEY. TEMPERATURES AT 9 AM WERE IN THE MID 40S TO MID 50S.

WEAK UPPER LEVEL RIDGE MOVING THROUGH THE AREA TODAY. SC DECK
OVER THE INTERIOR IS FAIRLY THIN WITH THE BASES IN THE 6000-7000
FOOT RANGE AND THE TOPS WELL BELOW 10,000 FEET ON THE CAMP MUIR
WEBCAM. THE COMBINATION OF LARGE BREAKS IN THE CLOUD COVER
ALREADY...UPPER LEVEL RIDGE MOVING THROUGH AND THE CLOUD DECK
BEING PRETTY THIN WILL STAY WITH THE PARTLY SUNNY WORDING FOR THE
INTERIOR ZONES TODAY FROM THE PUGET SOUND EASTWARD. WILL DO A
QUICK UPDATE TO DECREASE THE CLOUD COVER FOR THE ZONES WEST OF
THE SOUND. EVEN WITH THE REDUCED CLOUD COVER TEMPERATURES ALOFT
ARE NOT VERY WARM...MODEL 850 MB TEMPS PLUS 2 TO PLUS 4C...SO WILL
STAY WITH THE FORECAST HIGH TEMPERATURE RANGE OF UPPER 50S TO MID
60S.

UPPER LEVEL RIDGE EAST OF THE AREA TONIGHT WITH A WEAK UPPER LEVEL
TROUGH APPROACHING THE COAST. THE TROUGH WILL BE CLOSE ENOUGH TO
THE COAST BY EARLY FRIDAY MORNING TO PUT A CHANCE OF SHOWERS IN
THE FORECAST AFTER MIDNIGHT TONIGHT. TROUGH MOVING THROUGH WESTERN
WASHINGTON ON FRIDAY FOR WIDESPREAD SHOWER ACTIVITY. RAINFALL
AMOUNTS WILL NOT BE MUCH...A TENTH OR SO OVER THE INTERIOR AND
SLIGHTLY MORE OVER THE MOUNTAINS. HIGHS WILL BE A FEW DEGREES
COOLER THAN TODAY ON FRIDAY WITH MID AND UPPER 50S COMMON.

SHOWER ACTIVITY DRYING UP QUICKLY FRIDAY EVENING AS AN UPPER LEVEL
RIDGE BUILDS OFFSHORE. RIDGE CONTINUING TO BUILD ON SATURDAY WITH
TEMPERATURES ALOFT WARMING. MODEL 850 MB TEMPERATURES IN THE PLUS
5 TO 8C RANGE BY 00Z SUNDAY. SURFACE GRADIENTS REMAINING
NORTHWESTERLY SO AFTERNOON SEABREEZES WILL CAP THE HIGHS ON
SATURDAY IN THE 60S FOR THE MOST PART WITH LOCATIONS NEAR THE
WATER IN THE UPPER 50S. NO CHANGES TO THE FORECAST THIS MORNING
OTHER THAN THE CLOUD COVER FOR TODAY. FELTON

.LONG TERM...PREVIOUS DISCUSSION FOLLOWS. THE UPPER RIDGE WILL MOVE
TO AROUND THE COAST SUNDAY AND THEN INLAND MONDAY. THERE WILL BE
SUNSHINE BOTH DAYS. HIGHS SHOULD BE IN THE MID TO UPPER 70S OVER
MUCH OF THE AREA ON SUNDAY AND INTO THE LOWER 80S ON MONDAY. IT
LOOKS LIKE THE RIDGE WILL MOVE EAST AND BREAK DOWN AFTER
THAT...BUT MODELS DIFFER ON HOW THAT WILL HAPPEN. MOIST SOUTHERLY
FLOW ALOFT WEST OF THE RIDGE COULD BRING SOME SHOWERS AND
CONVECTION INTO THE AREA MONDAY NIGHT OR TUESDAY...OR POSSIBLY A
MORE ORGANIZED SYSTEM WILL ARRIVE FROM THE WEST. AT ANY
RATE...THERE IS A CHANCE OF PRECIPITATION AGAIN MONDAY NIGHT
THROUGH WEDNESDAY. MCDONNAL

&&

.AVIATION...UPPER LEVEL RIDGE AXIS PASSING WRN WA THIS
AFTN...FOLLOWED BY THE PASSAGE OF AN UPPER TROUGH AXIS ON FRI
MORNING. AIR MASS SOMEWHAT MOIST AND STABLE TODAY...BECOMING MORE
MOIST AND MORE UNSTABLE ON FRI. SHOWERS AND FAIRLY WIDESPREAD IFR
CONDS EXPECTED FRI MORNING. LIGHT AND VARIABLE FLOW ALOFT
TODAY...BECOMING LIGHT NW ON FRI.

KSEA...CIGS RISING THIS AFTN WITH DAYTIME HEATING...GENERALLY
REMAINING AT OR ABOVE 5000 FEET THROUGH THIS EVNG. PUGET SOUND
CONVERGENCE ZONE MAY SLIP JUST SOUTH OF THE TERMINAL THIS
EVNG...BRINGING A SHIFT TO NORTHERLY WINDS ARND 02Z...THEN LASTING
FOR A FEW HOURS. THE PASSAGE OF A FRONT ON FRI MORNING WILL ENHANCE
MOIST LOW-LEVEL ONSHORE FLOW...BRINGING IFR CIGS ON FRI MORNING IN
THE 1000-2000 FOOT RANGE...ALONG WITH A FEW HOURS OF RAIN. CIGS
LIFTING ON FRI AFTN TO NEAR 030-040...BUT HAVING A HARD TIME
ACTUALLY SCATTERING OUT ON FRI AFTN.       HANER

&&

.MARINE...THE EASTWARD PASSAGE OF A FRONT WILL START ENHANCE ONSHORE
FLOW THIS AFTERNOON AND EVENING. THE FRONT WILL PASS ON FRIDAY
MORNING...FOLLOWED BY A RENEWED ROUND OF ONSHORE FLOW ON FRIDAY
AFTERNOON AND EVENING. A TURN TO NORTHERLY ONSHORE FLOW IS EXPECTED
ON SATURDAY. NORTHERLY OFFSHORE FLOW IS EXPECTED ON SUNDAY.   HANER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 5 PM THIS AFTERNOON TO 8 AM PDT FRIDAY
     FOR EAST ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA.

     SMALL CRAFT ADVISORY FROM 2 PM THIS AFTERNOON TO 11 PM PDT THIS
     EVENING FOR WEST ENTRANCE U.S. WATERS STRAIT OF JUAN DE
     FUCA.

     SMALL CRAFT ADVISORY FROM 2 PM THIS AFTERNOON TO 8 AM PDT FRIDAY
     FOR CENTRAL U.S. WATERS STRAIT OF JUAN DE FUCA.

&&

$$

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