Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 192341
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PST WED NOV 19 2014

.SYNOPSIS...A FRONT WILL BRING SOME RAIN TONIGHT. ANOTHER STRONGER
FRONT WILL IMPACT THE AREA ON FRIDAY AND FRIDAY NIGHT...BRINGING
RAIN...WIND...AND SNOW TO THE MOUNTAINS. ADDITIONAL WEATHER SYSTEMS
WILL ARRIVE EVERY DAY OR TWO THROUGH THE MIDDLE OF NEXT WEEK.

&&

.SHORT TERM...AS A FRONTAL SYSTEM ASSOCIATED WITH A SHORTWAVE TROUGH
MOVES INTO THE AREA...PRECIPITATION WILL SPREAD INTO WESTERN
WASHINGTON FROM SOUTHWEST TO NORTHEAST OVERNIGHT. THERE IS A CHANCE
OF FREEZING RAIN IN THE PASSES DUE TO EASTERLY FLOW BRINGING IN COLD
AIR AT LOWER LEVELS. THURSDAY MORNING THE PRECIPITATION WILL ALSO
TAPER OFF FROM SOUTHWEST TO NORTHEAST AS THE SYSTEM MOVES OUT OF THE
AREA. LINGERING SHOWERS ARE POSSIBLE ON THURSDAY AS THE AIR MASS
WILL BE A BIT UNSTABLE. THURSDAY NIGHT WILL BE FAIRLY DRY AS A WEAK
SURFACE LOW MOVES SOUTHEAST INTO NORTHERN CALIFORNIA.

ON FRIDAY AND FRIDAY NIGHT...A STRONGER COLD FRONT STEMMING FROM A
DEEP LOW IN THE GULF OF ALASKA WILL IMPACT THE AREA. WIND ADVISORY
LEVEL CONDITIONS ARE POSSIBLE FRIDAY ON THE COAST...AND FRIDAY NIGHT
IN THE NORTH INTERIOR WITH THIS SYSTEM. AREAS IN THE NORTH CASCADES
ABOVE 4000 FEET COULD ALSO SEE A GOOD AMOUNT OF SNOWFALL WITH THIS
SYSTEM.

ON SATURDAY A WEAK SHORTWAVE TROUGH WILL MOVE THROUGH WESTERN
WASHINGTON...LIKELY CONTINUING THE PRECIPITATION. JSMITH

&&

.LONG TERM...A COUPLE MORE SHORTWAVE TROUGHS WILL LIKELY IMPACT THE
AREA ON SUNDAY AND MONDAY...KEEPING BREEZY CONDITIONS AND
PRECIPITATION IN THE FORECAST. ON TUESDAY...MODELS ARE BEGINNING TO
AGREE THAT A PLUME OF MOISTURE CARRIED BY THE JET STREAM WILL IMPACT
THE NORTHWEST...AS PREDICTED BY THE ECMWF YESTERDAY. HOWEVER...A LOT
OF UNCERTAINTY EXISTS AS TO WHERE THIS MOISTURE WILL COME
ASHORE...THE ECMWF HAS IT HITTING OREGON WHEREAS THE GFS HAS IT
IMPACTING NORTHWEST WASHINGTON AND SOUTHWEST BC. THERE IS ALSO
UNCERTAINTY AS TO WHETHER IT WILL BE ACCOMPANIED BY A SURFACE LOW
PRESSURE SYSTEM.

MODELS DISAGREE ON ABOUT JUST ABOUT EVERYTHING WEDNESDAY AND
BEYOND...SO THE FORECAST IS VERY UNCERTAIN AT THIS POINT. JSMITH

&&

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

&&

.AVIATION...A COLD FRONT OVER THE OREGON OFFSHORE WATERS WILL MOVE
NE ACROSS W WA TONIGHT...WITH RAIN SPREADING OVER SW WA THIS EVENING
AND THEN OVER THE N HALF OF W WA AFTER 06Z. CIGS BKN060-100 AHEAD OF
THE FRONT WILL LOWER TO MVFR LEVELS WITH AND BEHIND THE FRONT. LOCAL
IFR CIGS ARE POSSIBLE AFTER 12Z. FROPA ALONG A HQM-CLS LINE WILL BE
AROUND 08Z...THEN AT BLI AROUND 15Z. WEAK POST-FRONTAL WESTERLY FLOW
ALOFT WILL PREVAIL ON THURSDAY. A MOIST AIR MASS WILL KEEP CIGS
MAINLY IN THE 2000-5000 FOOT RANGE.

KSEA...GOOD VFR CONDITIONS WITH CIGS ABOVE BKN080-100 WILL CONTINUE
THROUGH ABOUT 05Z TONIGHT. RAIN FROM THE APPROACHING FRONT SHOULD
REACH THE TERMINAL AFTER 05Z...WITH CIGS GRADUALLY LOWERING TO MVFR
OVC015-025 AROUND 09Z...THEN CONTINUING THROUGH 18Z. SURFACE WINDS
ARE EXPECTED TO SHIFT FROM LIGHT N TO S 5-10 KT BY 02Z AND CONTINUE
THROUGH TONIGHT. KAM

&&

.MARINE...A COLD FRONT APPROACHING FROM THE SOUTHWEST WILL MOVE
ACROSS W WA LATE TONIGHT. MODERATE SOUTHEAST FLOW WILL BRING SMALL
CRAFT ADVISORY WINDS OVER MOST WATERS. POST FRONT SCA WINDS WILL
CONTINUE OVER MOST WATERS THROUGH THURSDAY MORNING.

A WEAKER TRAILING SYSTEM WILL HEAD TOWARD N CA ON THURSDAY AND WILL
HAVE NO IMPACT ON THE PACNW.

MODELS REMAIN FAIRLY CONSISTENT IN BRINGING A STRONGER FRONTAL
SYSTEM FROM THE WEST ON FRIDAY. HOWEVER THE WRF-GFS AND HIRES-ARW-W
HAVE BACKED OFF SLIGHTLY ON THE DURATION OF GALE FORCE WINDS...WITH
THE STRONGEST WINDS OVER THE COASTAL WATERS FRIDAY AFTERNOON...AND
OVER THE NORTH INTERIOR WATERS FRIDAY EVENING.

WESTERLY FLOW ALOFT OVER THE NE PACIFIC SATURDAY THROUGH MONDAY WILL
BRING SEVERAL WEAK SYSTEMS ACROSS THE AREA. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY ALL WATERS EXCEPT THE CENTRAL STRAIT.
     GALE WATCH COAST FRIDAY.

&&

$$

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