Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 030347
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
845 PM PDT MON MAY 2 2016

.SYNOPSIS...SOUTHERLY FLOW ALOFT WILL BRING INCREASING CLOUDS AND
SCATTERED SHOWERS TONIGHT WITH A CHANCE OF AN EVENING THUNDERSTORM. A
STALLED FRONTAL BOUNDARY WILL MAINTAIN A CHANCE OF SHOWERS OVER
WESTERN WASHINGTON THROUGH THURSDAY ALONG WITH LOWER DAYTIME
TEMPERATURES. DRY AND WARMER WEATHER IS EXPECTED BY THE WEEKEND.

.SHORT TERM...MID LEVEL CLOUDS STREAMING NORTH HAVE DROPPED THE ODD
TRACE HERE AND THERE...AND A FEW 0.01 INCH AMOUNTS IN THE CASCADES.
PARTLY CLOUDY WITH A CHANCE OF SHOWERS SEEMS TO COVER IT WELL. ONE
CELL MOVING ALONG THE COAST DEVELOPED THUNDER OVER VANCOUVER ISLAND
SO AN ISOLATED THUNDERSTORM IS ALSO POSSIBLE TONIGHT...MAINLY OVER
WESTERN SECTIONS.

MEANWHILE AT THE SURFACE ONSHORE FLOW HAS INCREASED AND SOME
AMOUNT OF LOW LEVEL PUSH IS LIKELY TONIGHT. GIVEN THE CURRENT
STRENGTH OF GRADIENTS WOULD NOT BE SURPRISED TO SEE STRATUS GET TO
KNUW AND KSHN TONIGHT...PERHAPS ALL THE WAY TO THE WEST SIDE OF
PUGET SOUND. THE MARINE PUSH IS LIKELY TO BE COMPLETED TUESDAY NIGHT
AS GRADIENTS INCREASE EVEN MORE.

IN THE BROADER PATTER AN UPPER LEVEL TROUGH WILL APPROACH THE AREA
TUESDAY THEN SLOWLY MOVE ACROSS WASHINGTON WEDNESDAY AND THURSDAY.
THERE WILL BE CLOUDS AND SCATTERED SHOWERS ALL THREE DAYS. ASIDE
FROM THE CLOUDINESS...THE MOST NOTICEABLE EFFECT WILL BE LOWER
TEMPERATURES. INLAND HIGHS WILL BE IN THE LOW 70S ON TUESDAY WITH
LOW 60S ON THE COAST UNDER CLOUDS. MORE CLOUDS EVERYWHERE WILL KEEP
HIGHS IN THE 60S MOST PLACES WEDNESDAY AND THURSDAY. BURKE

.LONG TERM...PREVIOUS DISCUSSION...THE GFS/ECMWF AGREE ON A RIDGE
NOSING NE OVER THE REGION FRIDAY AND SATURDAY. THIS WILL PROVIDE DRY
WEATHER AND YET ANOTHER WARMING TREND. BY SUNDAY...THE ECMWF IS MUCH
MORE AGGRESSIVE WITH A BRUSH BY TROUGH. THIS SOLUTION WOULD MOST
LIKELY STILL BE DRY BUT WOULD INDUCE A STRONG MARINE PUSH WITH
COOLER TEMPERATURES. THE GFS AND CANADIAN HAVE A STRONGER RIDGE INTO
MONDAY WITH THE TROUGH FURTHER N. TEMPERATURES SUNDAY AND MONDAY ARE
A COMPROMISE BUT TILTED TOWARD A SLIGHT WARMING TREND. MERCER

&&

.AVIATION...SOUTHERLY FLOW ALOFT OVER WESTERN WASHINGTON THIS
EVENING...BETWEEN THE UPPER HIGH OVER THE NORTHERN ROCKY MOUNTAINS
AND OFFSHORE UPPER TROUGH ALONG 138W. THE AIR MASS IS SOMEWHAT
MOIST ABOVE 10000 FT WITH WEAK INSTABILITY...PRODUCING ISOLATED
SHOWERS. THIS PATTERN WILL CONTINUE TONIGHT AND TUESDAY...WITH LOW
LEVEL ONSHORE FLOW DEVELOPING LATE TUESDAY AS THE UPPER TROUGH
APPROACHES THE PACIFIC NORTHWEST.

SCATTERED TO BROKEN ALTOCUMULUS ACROSS THE FORECAST AREA THIS
EVENING WITH CEILINGS AT OR ABOVE 10000 FT. THERE ARE ISOLATED
SHOWERS AND SCATTERED VIRGA FALLING FROM THESE CLOUDS. MARINE
STRATUS SHOULD MOVE NORTH UP THE COAST LATER TONIGHT BRINGING
LOW-END MVFR AND LOCAL IFR CONDITIONS TO THE COASTAL
TERMINALS...AND PROBABLY MOVE INLAND THROUGH THE CHEHALIS GAP TO
NEAR SHELTON FOR A BRIEF PERIOD EARLY TUESDAY MORNING. OTHERWISE
CEILINGS SHOULD REMAIN MOSTLY AT OR ABOVE 10000 FT.

KSEA...SOUTHWEST WIND 8-13 KT GUSTING 20 KT THIS EVENING...
BECOMING SOUTH 3-8 KT AFTER MIDNIGHT...THEN SOUTHWEST 8-14 KT
AGAIN TUESDAY AFTERNOON. CEILING SHOULD MOSTLY REMAIN AT OR ABOVE
10000 FT. MCDONNAL

&&

.MARINE...A THERMAL TROUGH IS OVER THE INTERIOR LOWLANDS OF
WESTERN WASHINGTON THIS EVENING...WITH WEAK ONSHORE FLOW
DEVELOPING ACROSS THE FORECAST AREA. SMALL CRAFT ADVISORY
WESTERLIES SHOULD GRADUALLY INCREASE TO 20 TO 30 KT IN THE CENTRAL
AND EASTERN STRAIT OF JUAN DE FUCA TONIGHT.

ONSHORE FLOW WILL INCREASE TUESDAY AND TUESDAY EVENING AS THE
THERMAL TROUGH MOVES EAST OF THE CASCADES AND HIGH PRESSURE BUILDS
OVER THE OFFSHORE WATERS. THERE IS A GOOD CHANCE OF GALE
WESTERLIES IN THE CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA
TUESDAY AFTERNOON AND EVENING...WITH SMALL CRAFT ADVISORY WINDS
LIKELY OVER ALL OTHER MARINE ZONES EXCEPT PUGET SOUND AND HOOD
CANAL. A GALE WATCH WILL BE ISSUED FOR THE CENTRAL AND EASTERN
STRAIT THIS EVENING. ONSHORE FLOW WILL CONTINUE WEDNESDAY THROUGH
FRIDAY. MCDONNAL

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...GALE WATCH FROM TUESDAY AFTERNOON THROUGH LATE TUESDAY NIGHT FOR
     CENTRAL U.S. WATERS STRAIT OF JUAN DE FUCA-EAST ENTRANCE
     U.S. WATERS STRAIT OF JUAN DE FUCA.

     SMALL CRAFT ADVISORY UNTIL 3 PM PDT TUESDAY FOR CENTRAL U.S.
     WATERS STRAIT OF JUAN DE FUCA-EAST ENTRANCE U.S. WATERS
     STRAIT OF JUAN DE FUCA.

&&

$$

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