Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 200501
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 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...A COLD FRONT WILL LIFT NORTH THROUGH WESTERN WA
TONIGHT BRINGING A LITTLE RAIN TO THE AREA. THE FRONT IS NOW
REACHING KHQM...BUT THERE ARE A FEW LIGHT SHOWERS ALSO AFFECTING THE
NORTH INTERIOR. EAST WINDS WILL KEEP TEMPS BELOW FREEZING IN THE
PASSES AND MAY SEE FREEZING RAIN AT SNOQUALMIE AND STEVENS PASS.
TEMPS WILL REMAIN ABOVE FREEZING ACROSS THE LOWLANDS TONIGHT. THIS
FRONT WILL EXIT NORTH THURSDAY MORNING WITH RAIN TAPERING DOWN. A
WEAK UPPER TROUGH WILL SHIFT INLAND FOR JUST ISOLATED TO SCATTERED
SHOWERS ACROSS THE REGION DURING THE AFTERNOON.

A STRONGER PAC SYSTEM WILL BRING WET AND WINDY WEATHER TO WESTERN WA
ON FRI. SO FAR MODELS ARE PRETTY CONSISTENT WITH THIS SYSTEM. RAIN
WILL BEGIN ON THE COAST FRI MORNING...WITH RAIN SPREADING INLAND BY
THE AFTERNOON. IT WILL BE WINDY ALONG THE COAST AND NORTH INTERIOR.
RAIN WILL CONTINUE THROUGH THE EVENING AS THE COLD FRONT MOVES
INLAND. THE SNOW LEVEL WILL LOWER TO AROUND 4000 FT FRIDAY NIGHT AND
STEVENS PASS MAY SEE A FEW INCHES OF SNOW...WITH WINTER WEATHER
ADVISORY AMOUNTS POSSIBLE AT MOUNT BAKER. THE AIR MASS WILL REMAIN
COOL AND UNSETTLED THROUGH EARLY SAT MORNING AS THE UPPER TROUGH
PASSES THROUGH.

ONSHORE FLOW WILL CONTINUE ON SAT FOR ADDITIONAL SHOWERS ACROSS THE
REGION. MAY ALSO SEE A PUGET SOUND CONVERGENCE ZONE DEVELOP IN
SNOHOMISH/KING COUNTIES...WITH MORE SNOW EXPECTED IN THE MOUNTAINS.
33

.LONG TERM...PREVIOUS DISCUSSION...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
NORTHEAST ACROSS WESTERN WASHINGTON TONIGHT. CEILINGS BKN060-100
AHEAD OF THE FRONT WILL LOWER TO MVFR LEVELS WITH AND BEHIND THE
FRONT. LOCAL IFR CIGS ARE POSSIBLE AFTER 12Z. WEAK POST-FRONTAL
WESTERLY FLOW ALOFT WILL PREVAIL ON THURSDAY. A MOIST AIR MASS WILL
KEEP CEILINGS MAINLY IN THE 2000-5000 FOOT RANGE.

KSEA...GOOD VFR CONDITIONS WITH CEILINGS ABOVE BKN080-100 WILL
CONTINUE THROUGH ABOUT 08Z TONIGHT. RAIN FROM THE APPROACHING FRONT
SHOULD REACH THE TERMINAL AROUND 08Z WITH MVFR CEILINGS AFTER 09Z.
WINDS SOUTHEAST 6-10 KT. CHB

&&

.MARINE...A COLD FRONT APPROACHING FROM THE SOUTHWEST WILL MOVE
ACROSS WESTERN WASHINGTON LATE TONIGHT. MODERATE SOUTHEAST FLOW WILL
BRING SMALL CRAFT ADVISORY WINDS TO MOST WATERS. POST FRONT ADVISORY
LEVEL WINDS WILL CONTINUE THROUGH THURSDAY MORNING.

MODELS REMAIN 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/CHB

&&

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

&&

$$

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