Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 182340
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PST TUE NOV 18 2014

.SYNOPSIS...AS AN UPPER RIDGE MOVES EAST TONIGHT AND WEDNESDAY...THE
COLD AND DRY WEATHER WILL COME TO AN END. A WEAK FRONTAL SYSTEM WILL
MOVE THROUGH THE AREA WEDNESDAY NIGHT AND ANOTHER STRONGER SYSTEM
WILL MOVE THROUGH ON FRIDAY. BOTH WILL BRING RAIN AND LOCALLY WINDY
CONDITIONS TO WESTERN WA. WEAK SYSTEMS WILL CONTINUE TO IMPACT THE
AREA THROUGH EARLY NEXT WEEK.

&&

.SHORT TERM...A SHARP UPPER LEVEL RIDGE OVER WESTERN WASHINGTON WILL
MOVE EAST THIS EVENING AND INTO WEDNESDAY...MAKING WAY FOR A
SHORTWAVE TROUGH AND ITS ASSOCIATED FRONTAL SYSTEM TO ENTER THE AREA
WEDNESDAY NIGHT AND BRING AN END TO THE COLD AND DRY SPELL WE HAVE
BEEN HAVING. TEMPERATURES WILL MODERATE A BIT AND RAIN IS LIKELY
ACROSS THE AREA WITH THIS FRONTAL SYSTEM. WINDS ON THE COAST WILL
SWITCH FROM SOUTHEASTERLY TO SOUTHWESTERLY LATE WEDNESDAY NIGHT WITH
THE COLD FRONTAL PASSAGE AND SOUTH WINDS WILL PICK UP IN THE NORTH
INTERIOR AS WELL.

THURSDAY AND THURSDAY NIGHT A BREAK IN THE RAIN IS LIKELY AS THE
SHORTWAVE TROUGH MOVES TO THE NORTHEAST AND ANOTHER UPPER LEVEL
TROUGH MOVES INTO NORTHERN CALIFORNIA. HOWEVER...SKIES WILL REMAIN
MOSTLY CLOUDY.

ON FRIDAY...ANOTHER SLIGHTLY STRONGER AND WETTER FRONTAL SYSTEM WILL
MOVE INTO WESTERN WASHINGTON. SNOW LEVELS WITH THIS SYSTEM WILL BE
LOWER...POSSIBLY IN THE 4000 FOOT RANGE...SO MORE OF THE
PRECIPITATION IN THE MOUNTAINS WILL FALL AS SNOW.
HOWEVER...UNCERTAINTY IN THE SNOW LEVEL IS HIGH AT THIS POINT.
LOCALLY WINDY CONDITIONS WILL LIKELY OCCUR ACROSS THE AREA WITH
LOWER PRESSURE IN THE NORTH AND HIGHER PRESSURE IN THE SOUTH. JSMITH

&&

LONG TERM...A SERIES OF WEAK SYSTEMS WILL MOVE THROUGH THE AREA
SATURDAY THROUGH MONDAY NIGHT...BRINGING A CHANCE OF RAIN INTO THE
AREA. TUESDAY...THE ECMWF HAS A PLUME OF MOISTURE CARRIED BY THE JET
STREAM HITTING THE NORTHWEST...WHEREAS THE GFS SHOWS A DEEP SURFACE
LOW DEVELOPING OFF THE COAST OF ALASKA AND ITS ASSOCIATED FRONTAL
SYSTEM MOVING INTO THE NORTHWEST. UNCERTAINTY ON TUESDAY IS HIGH AND
WE WILL SEE IF EITHER OF THESE SOLUTIONS PAN OUT. JSMITH

&&

.HYDROLOGY...RIVER FLOODING IS NOT EXPECTED IN THE NEXT 7 DAYS.

&&

.AVIATION...A STRONG UPPER LEVEL RIDGE WILL REMAIN OVER WESTERN
WASHINGTON THROUGH TONIGHT. A SURFACE RIDGE OVER EASTERN WASHINGTON
WILL MAINTAIN DRY EASTERLY LOW LEVEL OFFSHORE FLOW. THE LOWER AIR
MASS WILL REMAIN DRY AND STABLE WITH UNRESTRICTED VFR CONDITIONS.
HIGH CLOUDS WILL CONTINUE OVER THE AREA THIS EVENING...IN ADVANCE OF
AN APPROACHING COLD FRONT. CLOUD LAYERS WILL GRADUALLY LOWER TO
AROUND 10000 FEET LATE TONIGHT THROUGH WEDNESDAY. THE COLD FRONT
WILL MOVE ACROSS W WA WEDNESDAY NIGHT WITH CIGS LOWERING TO MVFR TO
IFR LEVELS.

KSEA...HIGH CLOUDS WILL CONTINUE OVER THE AREA THOUGH 08Z WITH
UNRESTRICTED VISIBILITY. MID LEVEL CLOUDS AROUND 10000 FEET WILL
INCREASE AFTER 08Z...AHEAD OF A DEVELOPING FRONT OFFSHORE. SURFACE
WINDS WILL BE 6 KT OR LESS FAVORING E TO SE. KAM

&&

.MARINE...THE SURFACE RIDGE OVER EASTERN WASHINGTON COMBINED WITH
LOWER PRESSURE FROM A DEVELOPING FRONT OFFSHORE WILL MAINTAIN
EASTERLY FLOW ACROSS WESTERN WASHINGTON THROUGH WEDNESDAY MORNING.

A COLD FRONT WILL APPROACH FROM THE SOUTHWEST ON WEDNESDAY... THEN
MOVE NORTHEAST ACROSS THE AREA WEDNESDAY NIGHT. MODERATE SOUTHEAST
FLOW WILL DEVELOP WITH SMALL CRAFT ADVISORY WINDS OVER THE COASTAL
WATERS AND THE NORTHERN INTERIOR WATERS. A STRONGER FRONTAL SYSTEM
ARRIVING FROM THE WEST ON FRIDAY COULD GENERATE SOUTHERLY GALES OVER
THE COASTAL AND NORTHERN INTERIOR WATERS. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY WEST ENTRANCE AND ADJACENT COASTAL ZONE
      PZZ150.

&&

$$

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YOU CAN SEE AN ILLUSTRATED VERSION OF THIS FORECAST DISCUSSION AT
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