Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 251202
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
400 AM PST THU DEC 25 2014

.SYNOPSIS...WEAK WEATHER SYSTEMS MOVING BY THE AREA WILL KEEP A
CHANCE OF SHOWERS IN THE FORECAST TODAY AND FRIDAY. A STRONGER AND
MORE ORGANIZED SYSTEM WILL MOVE THROUGH WESTERN WASHINGTON SATURDAY
AND SATURDAY NIGHT WITH SIGNIFICANT SNOW IN THE MOUNTAINS. SUNDAY
WILL BE A TRANSITION DAY TO DRIER AND COOLER WEATHER WHICH WILL LAST
WELL INTO NEXT WEEK.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS CLOUDY SKIES FOR THE MOST PART
OF WESTERN WASHINGTON EARLY THIS MORNING. A CONVERGENCE ZONE FROM
NEAR PORT TOWNSEND DOWN TO NEAR NORTH BEND HAS STAYED INTACT
OVERNIGHT. OUTSIDE OF THE CONVERGENCE ZONE JUST SOME ISOLATED
SHOWERS. A FEW BREAKS IN THE CLOUD COVER ALLOWED THE TEMPERATURE TO
DROP INTO THE UPPER 20S OVER THE SOUTHWEST INTERIOR AT 3 AM/11Z.
MOST OF THE REMAINDER OF THE AREA WAS IN THE 30S.

UPPER LEVEL RIDGE REMAINING WELL OFFSHORE TODAY WITH A WEAK SYSTEM
CURRENTLY OVER VANCOUVER ISLAND MOVING DOWN OVER WESTERN WASHINGTON
IN THE NORTHWESTERLY FLOW ALOFT KEEPING A CHANCE OF SHOWERS IN THE
FORECAST. WESTERLY WINDS THROUGH THE STRAIT OF SLOWLY DECREASED
OVERNIGHT AND WILL CONTINUE TO WEAK THIS MORNING. THIS WILL BRING
ABOUT AN END TO THE CONVERGENCE ZONE THIS MORNING. A FEW BREAKS IN
THE CLOUD COVER ALLOWED PATCHY FOG TO FORM FROM ABOUT TACOMA TO
CHEHALIS. THIS WILL DISSIPATE LATER THIS MORNING. HIGH TEMPERATURES
WILL BE NEAR NORMAL...IN THE 40S.

ANOTHER WEAK UPPER LEVEL SYSTEM MOVING OVER THE TOP OF THE RIDGE
LATE TONIGHT INTO FRIDAY KEEPING A CHANCE OF SHOWERS ALONG THE COAST
AND OVER THE NORTHERN PORTION OF THE AREA TONIGHT AND OVER THE
REMAINDER OF THE AREA ON FRIDAY. THE AIR MASS OVER WESTERN
WASHINGTON WILL REMAIN COOL WITH MODEL 850 MB TEMPERATURES BETWEEN
-1 AND -6C OVERNIGHT SO THERE IS A CHANCE THE COLDER LOCATIONS WILL
ONCE AGAIN BE BELOW FREEZING FRIDAY MORNING. MOST OF THE AREA WILL
SEE LOWS IN THE 30S. HIGHS ON FRIDAY WILL BE SIMILAR TO TODAYS
READINGS...IN THE 40S.

A STRONGER AND MORE ORGANIZED SYSTEM WILL DROP DOWN FROM THE NORTH
ON SATURDAY THE THE PRECIPITATION OUT AHEAD OF THE SYSTEM REACHING
THE NORTHWEST INTERIOR BY FRIDAY NIGHT. WITH THE INCREASING CLOUD
COVER OUT AHEAD OF THE SYSTEM SPREADING OVER THE AREA LOWS FRIDAY
NIGHT WILL BE A COUPLE OF DEGREES WARMER WITH READINGS STAYING ABOVE
FREEZING...IN THE MID AND UPPER 30S.

SYSTEM MOVING INTO WESTERN WASHINGTON SATURDAY AND SATURDAY NIGHT
WITH RAIN OVER THE LOWLANDS. WITH THE SNOW LEVEL NEAR 2000 FEET THIS
SYSTEM WILL BRING SNOW TO THE MOUNTAINS WITH A FOOT OR MORE OF SNOW
SNOW EXPECTED BY SATURDAY NIGHT.

.LONG TERM...EXTENDED MODELS CONTINUING TO SHOW GOOD RUN TO RUN
CONSISTENCY IN THE 00Z MODEL CYCLE. AS HAS BEEN THE CASE FOR THE
LAST THREE MORNINGS THE ECMWF IS A LITTLE SLOWER IN KICKING THE
SYSTEM SOUTH OF THE AREA ON SUNDAY VERSUS THE FASTER GFS SOLUTION.
CURRENT FORECAST KEEPS A CHANCE OF SHOWERS OVER THE SOUTHERN PORTION
OF THE AREA ON SUNDAY AND NO REASON TO CHANGE THIS WITH THE CURRENT
MODELS. HIGH AMPLITUDE RIDGE BUILDING OFFSHORE SUNDAY AND SUNDAY
NIGHT WITH THE LOW LEVEL FLOW TRANSITIONING TO OFFSHORE DURING THE
DAY IN SUNDAY AS A STRONG SURFACE HIGH DEVELOPS OVER CENTRAL BRITISH
COLUMBIA. UPPER LEVEL RIDGE CONTINUES TO BUILD ON SUNDAY NIGHT WITH
THE SURFACE HIGH SAGGING SOUTH INTO SOUTHERN BRITISH COLUMBIA. THIS
WILL BE THE BEGINNING OF A DRY AND COOL SPELL IN THE WEATHER ACROSS
WESTERN WASHINGTON WITH THE UPPER LEVEL RIDGE REMAINING IN PLACE
THROUGH THE MIDDLE OF THE WEEK. SOME OUTFLOW NORTHEAST WINDS ARE
POSSIBLE IN THE BELLINGHAM AREA LATER SUNDAY INTO SUNDAY NIGHT BE
WILL BUT WILL DIE OFF QUICKLY ON MONDAY AS THE SURFACE HIGH
CONTINUES TO DRIFT SOUTH. HIGH TEMPERATURES MONDAY THROUGH WEDNESDAY
IN THE MID 30S TO LOWER 40S WILL BE COMMON WITH LOWS BELOW FREEZING
ACROSS THE ENTIRE AREA EACH NIGHT. FELTON

&&

.HYDROLOGY...FLOODING IS NOT EXPECTED FOR THE NEXT 7 DAYS.

&&

.AVIATION...NORTHERLY FLOW ALOFT WILL PREVAIL OVER WESTERN
WASHINGTON THROUGH TONIGHT...AS AN UPPER RIDGE REMAINS OVER THE
NORTHEAST PACIFIC. AT THE SURFACE...WEAK HIGH PRESSURE WILL BUILD
OVER THE REGION. THE AIR MASS WILL BE MOIST AND STABLE.

SCATTERED SHOWERS CONTINUE EARLY THIS MORNING MAINLY AT THE COAST
AND IN A WEAK PUGET SOUND CONVERGENCE ZONE. THE CONVERGENCE ZONE
SHOULD WEAKEN AND DISSIPATE EARLY THIS MORNING...REMAINING NORTH OF
SEATTLE. THERE IS A MIX OF CONDITIONS ACROSS THE FORECAST AREA...BUT
IN GENERALLY LOW LEVEL MOISTURE IS RESULTING IN MVFR TO HIGH-END IFR
CEILINGS WITH LOCAL FOG. THERE WILL BE MARGINAL IMPROVEMENT LATE
THIS AFTERNOON AND EVENING.

KSEA...SOUTH TO SOUTHEAST WIND 6 KT OR LESS. THE CONVERGENCE ZONE
SHOULD REMAIN NORTH OF BOTH KBFI AND KSEA.   MCDONNAL

&&

.MARINE...WINDS WILL EASE TODAY WITH WEAK HIGH PRESSURE OVER THE
REGION. SMALL CRAFT ADVISORIES WILL REMAIN IN EFFECT FOR THE COASTAL
WATERS AND WEST ENTRANCE STRAIT OF JUAN DE FUCA FOR HAZARDOUS SEAS
AS THE WINDS EASE.

A DISSIPATING FRONT WILL MOVE SLOWLY EAST ACROSS THE COASTAL WATERS
LATE TONIGHT AND FRIDAY. ANOTHER FRONT WILL MOVE THROUGH FROM THE
NORTHWEST ON SATURDAY...FOLLOWED BY ONSHORE FLOW. SMALL CRAFT
ADVISORY WINDS SHOULD BE WIDESPREAD. NORTHERLY OFFSHORE FLOW WILL
DEVELOP SUNDAY AND MONDAY AS HIGH PRESSURE MOVES SOUTH THROUGH
BRITISH COLUMBIA.

SOME OF THE HIGHER ASTRONOMICAL HIGH TIDES OF THE YEAR WILL OCCUR
THE NEXT FEW DAYS. WITH LIGHT WIND AND WEAK HIGH PRESSURE TODAY AND
FRIDAY...POSITIVE TIDAL ANOMALIES AND TIDAL OVERFLOW ARE UNLIKELY.
MCDONNAL

&&

.SEW WATCHES/WARNINGS/ADVISORIES...

WA...NONE.
PZ...SMALL CRAFT ADVISORY COASTAL WATERS AND WEST ENTRANCE STRAIT
       OF JUAN DE FUCA.
     SMALL CRAFT ADVISORY FOR ROUGH BAR GRAYS HARBOR BAR.

&&

$$

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








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