Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 010409
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
915 PM PDT TUE MAR 31 2015

.SYNOPSIS...AN UPPER TROUGH WILL BRING SHOWERS AND COOLER WEATHER
TONIGHT AND WEDNESDAY. SHOWERS WILL DIMINISH THURSDAY AS WEAK HIGH
PRESSURE BUILDS OVER THE AREA. A FRONTAL SYSTEM WILL AFFECT THE AREA
ON FRIDAY. AN UPPER LEVEL LOW WILL MAINTAIN A CHANCE OF SHOWERS
THROUGH THE WEEKEND.

&&

.SHORT TERM...SHOWERS HAVE DIMINISHED A BIT SINCE SUNDOWN EXCEPT
OVER THE CASCADES WHERE RADAR SHOWS THEM CONTINUING. PARADISE ON
MOUNT RAINIER PICKED UP A QUICK SEVEN INCHES SO HAVE EXTENDED THE
WINTER WEATHER ADVISORY TO THE CASCADES OF PIERCE AND LEWIS
COUNTIES. IT SEEMS LIKELY THE HEAVIEST SNOW WILL STILL BE IN THE
CONVERGENCE ZONE WHICH IN THE CASCADES APPEARS TO BE BETWEEN STEVENS
AND SNOQUALMIE PASSES. ANYWAY THE PATTERN IS SHOWERY AND HIT AND
MISS SO THE THREE TO NINE INCHES FORECAST IS PROBABLY GOOD ENOUGH.

UPPER FLOW TURNS MORE NORTHWESTERLY WEDNESDAY. ANOTHER IMPULSE WILL
MOVE THROUGH THE FLOW IN THE AFTERNOON WHICH SHOULD ENHANCE THE
SHOWERS. HIGHS WILL BE IN THE LOW TO MID 50S. AN UPPER RIDGE BUILDS
ON THURSDAY WHICH WILL ALLOW A BIT OF SUN AND SOME WARMING. THE NEXT
FRONT WILL SPREAD RAIN INTO THE AREA ON FRIDAY AFTERNOON. BURKE

.LONG TERM...PREVIOUS DISCUSSION...THE AIR MASS WILL REMAIN COOL AND
UNSTABLE THIS WEEKEND THROUGH EARLY NEXT WEEK AS AN UPPER LEVEL LOW
SPINS OFFSHORE. THIS SYSTEM WILL CONTINUE TO PUMP MOISTURE INTO
WESTERN WA FOR A CHANCE OF SHOWERS EACH DAY. THE UPPER LOW WILL
WEAKEN AND MOVE INLAND ON MONDAY. A WARM FRONT WILL THEN ARRIVE
MONDAY NIGHT OR TUE FOR MORE RAIN. THERE IS GOOD AGREEMENT SO FAR
BETWEEN THE GFS AND ECMWF. 33

&&

.AVIATION...A BROAD UPPER TROUGH OVER THE REGION THIS EVENING WILL
MOVE SLOWLY EAST TONIGHT...BUT ANOTHER SHORTWAVE UPPER TROUGH WILL
MOVE INTO WESTERN WASHINGTON WEDNESDAY AFTERNOON. MOIST ONSHORE FLOW
WILL CONTINUE AT LOW LEVELS. THE AIR MASS WILL REMAIN WEAKLY
UNSTABLE.

SCATTERED SHOWERS CONTINUE ACROSS WESTERN WASHINGTON AT 8 PM...
ESPECIALLY IN THE PUGET SOUND CONVERGENCE ZONE WHICH EXTENDED FROM
THE NORTHERN KITSAP PENINSULA EASTWARD ALONG THE BORDER OF SNOHOMISH
AND KING COUNTIES TO THE CASCADES CREST. CEILINGS WERE MOSTLY
HIGH-END MVFR TO LOW-END VFR IN THE CONVERGENCE ZONE WITH SCT-BKN025
BKN-OVC040 BKN-OVC080...AND ELSEWHERE GENERALLY SCT TO LOCALLY
BKN030-050 BKN-OVC100. THESE CONDITIONS WILL CONTINUE WITHOUT MUCH
CHANGE THROUGH WEDNESDAY...AND THERE IS A CHANCE FOR THUNDERSTORMS
AGAIN WEDNESDAY AFTERNOON.

KSEA...SOUTH TO SOUTHWEST WIND 6-14 KT THROUGH WEDNESDAY. CLOUD
COVER WILL PROBABLY CONTINUE TO BE SCT-BKN AROUND 3000 FT WITH BKN
LAYERS 5000-8000 FT.   MCDONNAL
&&

.MARINE...A RIDGE OVER THE OFFSHORE WATERS WILL MAINTAIN ONSHORE
FLOW TONIGHT AND WEDNESDAY...THEN MOVE TO THE WASHINGTON COAST
THURSDAY. AN UPPER SHORTWAVE MOVING THROUGH THE AREA LATE WEDNESDAY
AND WEDNESDAY NIGHT WILL PROBABLY RESULT IN SMALL CRAFT ADVISORY
WEST OR NORTHWEST WINDS OVER THE COASTAL WATERS AND IN THE CENTRAL
AND EASTERN STRAIT OF JUAN DE FUCA.

A COLD FRONT WILL MOVE THROUGH THE AREA FRIDAY...AND IT SHOULD
PRODUCE SMALL CRAFT ADVISORY SOUTHERLIES FOR MUCH OF THE FORECAST
AREA. A LOW OVER THE OFFSHORE WATERS OF BRITISH COLUMBIA ON SATURDAY
WILL MOVE SOUTHEAST TO THE WASHINGTON OFFSHORE WATERS ON SUNDAY. AT
THIS TIME IT LOOKS LIKE THERE WILL NOT BE MUCH WIND ASSOCIATED WITH
THIS FEATURE.   MCDONNAL

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WINTER WEATHER ADVISORY CASCADES OF SNOHOMISH AND KING
     COUNTIES...CASCADES OF PIERCE AND LEWIS COUNTIES.
PZ...SMALL CRAFT ADVISORY CENTRAL AND EAST STRAIT OF JUAN DE FUCA.
     SMALL CRAFT ADVISORY GRAYS HARBOR FOR ROUGH BAR.

&&

$$

YOU CAN SEE AN ILLUSTRATED VERSION OF THIS FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML




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