Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 050953 AAA
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
230 AM PDT THU MAY 5 2016

.SYNOPSIS...A TROUGH OF LOW PRESSURE WILL SHIFT EAST TODAY WITH
DECREASING CLOUDS AND ANY SHOWERS CONFINED TO THE CASCADES. HIGH
PRESSURE ALOFT WILL BUILD OVER THE AREA ON FRIDAY AND SATURDAY FOR
INCREASED SUNSHINE AND A RETURN TO ABOVE NORMAL TEMPERATURES. A
TROUGH WILL INDUCE COOLER ONSHORE FLOW SATURDAY NIGHT THROUGH MONDAY.

&&

.SHORT TERM...ANY ACTIVITY OUT THERE ACCORDING TO CURRENT RADAR IS
AT THIS POINT LIMITED TO EASTERN WASHINGTON...AND EVEN THAT IS
DISSIPATING. THE UPPER LEVEL TROUGH RESPONSIBLE FOR THIS WILL
GRADUALLY SHIFT NORTH AND EAST OF THE AREA TODAY. ANY SHOWERS THAT
DO DEVELOP TODAY WILL BE CONFINED TO THE CASCADES...ALTHOUGH POPS
GENERALLY EXPECTED TO BE SLIGHT TO LOW-END CHANCE.

AS INFLUENCE OF UPPER LEVEL RIDGE OVER THE PACIFIC STARTS TO FILTER
INTO THE AREA...LOOKING AT AN INCREASE OF 4 TO 7 DEGREES IN THE
EXPECTED HIGH TEMPERATURES FOR TODAY VS THOSE OF YESTERDAY. THIS
LOOKS TO BE THE DOMINANT WEATHER SYSTEM INTO THE WEEKEND...ALLOWING
FOR MODELS TO HINT AT THE PROSPECT OF A THERMAL PRESSURE TROUGH
DEVELOPING OVER WESTERN WASHINGTON FRIDAY. THIS WOULD ALLOW FOR
ONSHORE FLOW...HELPING TO BOOST TEMPERATURES BACK ABOVE NORMAL FOR
THIS TIME OF YEAR. THIS PERIOD OF OFFSHORE FLOW LOOKS TO BE VERY
BRIEF...AS HIGHS FOR SATURDAY...WHILE STILL ABOVE NORMAL...HINT AT
COOLING ALONG THE COAST AND THE STRAIT.

THE RIDGE STARTS TO BREAK DOWN SATURDAY NIGHT AND INTO SUNDAY AS A
TROUGH DIPS SOUTHWARD FROM CANADA. GFS AND ECMWF REMAIN IN LOCKSTEP
WITH EACH OTHER REGARDING FEATURE AND PROSPECT FOR SHOWERS. EXPECTED
PRECIP FROM BOTH MODELS LOOKS TO BE GENERALLY LIGHT...BUT DOES YIELD
BEST CHANCE FOR SHOWERS FOR THE ENTIRE FORECAST PERIOD. THIS FEATURE
IS ALSO EXPECTED TO KNOCK HIGH TEMPERATURES BACK DOWN INTO A MORE
SEASONABLE RANGE.

INHERITED FORECAST TAKES MUCH OF THE ABOVE INTO CONSIDERATION AND IS
ON TRACK. SOME MINOR TWEAKS...BUT OTHERWISE...NO SIGNIFICANT
CHANGES MADE. SMR


.LONG TERM...WESTERN WASHINGTON WILL FIND ITSELF ON THE BACK SIDE OF
THE UPPER LEVEL TROUGH AND ITS ASSOCIATED LOW AS IT DROPS DOWN EAST
OF THE CASCADES LATE SUNDAY NIGHT/EARLY MONDAY MORNING. THIS WILL
ALLOW FOR THE THREAT OF PRECIP TO LINGER INTO MONDAY...BUT GENERALLY
ALONG THE CASCADES. ONCE IT PASSES THROUGH...RIDGING STARTS TO BUILD
OVER THE PACIFIC...INFLUENCING WESTERN WASHINGTON WEATHER AS EARLY
AS MONDAY...AS HIGH TEMPERATURES ALREADY START TO CLIMB UP ONCE
MORE. THIS SHOULD SOUND FAMILIAR...THUS REVEALING THE UPWARD TREND
FOR AFTERNOON HIGHS FOR AT LEAST THE FIRST HALF OF NEXT WEEK. SMR

&&

.AVIATION...SOUTHERLY FLOW ALOFT CONTINUES OVER WESTERN WASHINGTON
EARLY THIS MORNING...AHEAD OF A WEAK UPPER TROUGH OVER THE
OFFSHORE WATERS ALONG 127W. THE AIR MASS IS GENERALLY MOIST...
ESPECIALLY IN THE MID AND UPPER LEVELS. THE AIR MASS IS WEAKLY
UNSTABLE...MAINLY OVER THE CASCADES. THE AIR MASS WILL DRY THIS
AFTERNOON AND TONIGHT AS THE TROUGH WEAKENS AND MOVES INLAND.

CEILINGS OVER THE INTERIOR OF WESTERN WASHINGTON SHOULD MAINLY BE
5000 FT OR ABOVE ACROSS THE FORECAST AREA THIS MORNING...EXCEPT
LOCALLY AROUND 3000 FT WHERE STRATOCUMULUS FORMS IN THE MARINE
LAYER. CEILINGS WILL GENERALLY LIFT THIS AFTERNOON...BECOMING
MAINLY 12000 FT OR HIGHER BY THIS EVENING.

KSEA...NORTH WIND 4-10 KT THIS MORNING...RISING TO 8-14 KT THIS
AFTERNOON AND TONIGHT. CEILINGS WILL PROBABLY ONLY LOWER TO AROUND
3500-5000 FT THIS MORNING...THEN IMPROVE THIS AFTERNOON AND
TONIGHT. MCDONNAL

&&

.MARINE...NORTHWEST FLOW WILL PERSIST TODAY THROUGH
MONDAY...WITH HIGH PRESSURE OFFSHORE AND LOW PRESSURE EAST OF THE
CASCADES. THE STRONGEST WINDS WILL BE OVER THE COASTAL WATERS
MOST DAYS...WITH MARGINAL SMALL CRAFT ADVISORY IN EFFECT THROUGH
AT LEAST FRIDAY. MARGINAL SMALL CRAFT ADVISORY WESTERLIES ARE
LIKELY IN THE CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA THIS
EVENING AND AGAIN FRIDAY EVENING. THERE IS ALSO A GOOD CHANCE OF
WESTERLY GALES IN THE STRAIT OF JUAN DE FUCA SATURDAY EVENING
WHEN A STRONG MARINE PUSH OCCURS. MCDONNAL

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO MIDNIGHT PDT
     TONIGHT FOR CENTRAL U.S. WATERS STRAIT OF JUAN DE FUCA-EAST
     ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA.

     SMALL CRAFT ADVISORY UNTIL 6 PM PDT FRIDAY FOR COASTAL WATERS
     FROM CAPE FLATTERY TO JAMES ISLAND 10 TO 60 NM-COASTAL
     WATERS FROM JAMES ISLAND TO POINT GRENVILLE 10 TO 60 NM-
     COASTAL WATERS FROM POINT GRENVILLE TO CAPE SHOALWATER 10
     TO 60 NM.

&&

$$

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