Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 231215
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
415 AM PST TUE DEC 23 2014

.SYNOPSIS...A COLD FRONT MOVING DOWN OVER THE AREA FROM THE
NORTHWEST WILL STALL OVER WESTERN WASHINGTON TONIGHT INTO WEDNESDAY
MORNING. THE FRONT WILL MOVE SOUTH INTO OREGON WEDNESDAY AFTERNOON.
AN UPPER LEVEL RIDGE WILL BUILD OFFSHORE WEDNESDAY NIGHT AND REMAIN
OFFSHORE INTO THE WEEKEND. THE RIDGE WILL NOT BE STRONG ENOUGH TO
PREVENT WEAK SYSTEMS FROM MOVING OVER THE TOP OF THE RIDGE INTO
WESTERN WASHINGTON.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS A SURFACE LOW OFF THE SOUTHERN
PORTION OF HAIDA GWAII WITH THE COLD FRONT ASSOCIATED WITH THE LOW
EXTENDING SOUTH THROUGH THE NORTHERN TIP OF VANCOUVER ISLAND THEN
BENDING BACK TO THE SOUTHWEST INTO THE OFFSHORE WATERS OF WESTERN
WASHINGTON. LANGLEY HILL DOPPLER RADAR STARTING TO PICK UP
PRECIPITATION AHEAD OF THE COLD FRONT JUST WEST OF CAPE FLATTERY.
WITH CLOUDY SKIES OVER THE AREA AT 3 AM/11Z TEMPERATURES WERE QUITE
UNIFORM...IN THE 40S.

COLD FRONT WILL SLOWLY MOVE SOUTH AND EAST TODAY WITH THE FRONT
STILL OFFSHORE BY LATE THIS AFTERNOON. RAIN OUT AHEAD OF THE FRONT
WILL SPREAD OVER THE AREA TODAY. FLOW ALOFT INITIALLY NORTHWESTERLY
WHICH WILL CREATE A RAIN SHADOW OVER THE CENTRAL SOUND AT LEAST IN
THE MORNING HOURS. AS THE FLOW ALOFT TURNS MORE WESTERLY THIS
AFTERNOON THE RAIN SHADOW WILL FILL IN. TEMPERATURES WILL ONCE AGAIN
BE WELL ABOVE NORMAL...IN THE LOWER TO MID 50S FOR HIGHS.

COLD FRONT STALLING OVER WESTERN WASHINGTON TONIGHT WITH RAIN OVER
THE ENTIRE AREA. SNOW LEVELS AROUND 5000 FEET TODAY WILL SLOWLY
BEGIN TO LOWER TONIGHT DOWN TO AROUND 4000 FEET THEN DROP DOWN TO
AROUND 2000 FEET BY EARLY WEDNESDAY MORNING. PRECIPITATION RATES ARE
NOT THAT HIGH BY THE TIME THE SNOW LEVEL LOWERS BUT STILL A FEW
INCHES OF NEW SNOW IS LIKELY OVERNIGHT INTO WEDNESDAY MORNING.
TEMPERATURES WILL DROP INTO THE MID 40S OVERNIGHT.

COLD FRONT MOVING THROUGH WESTERN WASHINGTON WEDNESDAY MORNING WITH
THE STEADY RAIN GIVING WAY TO JUST A CHANCE OF SHOWERS IN THE
AFTERNOON. WITH THE COLDER AIR MASS OVER THE AREA BEHIND THE FRONT
TEMPERATURES WILL ACTUALLY REMAIN IN THE MID 40S ALL DAY. SNOW
LEVELS WILL CONTINUE TO HOVER AROUND 2000 FEET BUT THERE WILL NOT BE
MUCH PRECIPITATION LEFT ON WEDNESDAY TO CREATE SIGNIFICANT SNOWS IN
THE MOUNTAINS.

SHOWER ACTIVITY DRYING UP WEDNESDAY NIGHT WITH MOST OF THE SHOWER
CONFINED TO THE MOUNTAIN AFTER MIDNIGHT. THERE IS A CHANCE OF A
BRIEF CONVERGENCE ZONE OVER THE CENTRAL SOUND WEDNESDAY EVENING.
LOWS WILL BE IN THE 30S.

NOT MUCH GOING ON CHRISTMAS DAY WITH WEAK SURFACE HIGH PRESSURE OVER
THE AREA AND NORTHWESTERLY FLOW ALOFT. STILL COULD BE SOME LINGERING
SHOWERS EMBEDDED IN THE NORTHWEST FLOW ALOFT KEEPING A CHANCE OF
SHOWERS IN THE FORECAST IN THE MORNING HOURS. HIGH TEMPERATURES WILL
ONCE AGAIN BE IN THE MID 40S.

CONCERNING KING TIDES...SOME OF THE HIGHER ASTRONOMICAL HIGH TIDES
OF THE YEAR WILL OCCUR THIS WEEK ALONG WITH SLIGHT TIDAL ANOMALIES.
MINOR TIDAL OVERFLOW IS POSSIBLE EACH DAY FOR THE NEXT FEW DAYS WITH
THE BEST AND MOST WIDESPREAD CHANCES WEDNESDAY MORNING OVER PUGET
SOUND AND THE NORTHERN INLAND WATERS. SCHNEIDER

.LONG TERM...EXTENDED MODELS IN FAIRLY GOOD AGREEMENT THIS MORNING
WITH THE UPPER LEVEL RIDGE REMAINING OFFSHORE ON FRIDAY WITH A WEAK
SHORTWAVE MOVING OVER THE TOP OF THE RIDGE INTO WESTERN WASHINGTON
KEEPING AT LEAST A CHANCE OF RAIN IN THE FORECAST. RIDGE RETROGRADES
ON SATURDAY OPENING THE DOOR FOR A STRONGER SHORTWAVE TO MOVE DOWN
OUT OF THE NORTHWEST FRIDAY NIGHT AND SATURDAY. LOW LEVEL FLOW
REMAIN ONSHORE DURING THE PERIOD WITH MODEL 1000-850 MB THICKNESS
VALUES 1310-1320 METERS KEEPING THE PRECIPITATION IN THE FORM OF
RAIN IN THE LOWLANDS. COOLER AIR MOVING INTO THE AREA BEHIND THE
SHORTWAVE LATE SATURDAY NIGHT INTO SUNDAY WITH THE 1000-850 MB
THICKNESS VALUES STARTING TO APPROACH 1300 METERS DURING THE DAY ON
SUNDAY. PRECIPITATION STILL HASN`T CLEARED THE AREA COMPLETELY.
TEMPERATURES LOOK TO WARM DURING THE DAY FOR ANY SNOW IN THE LOWER
ELEVATIONS BUT SOME SNOW SHOWERS ABOVE 1000 FEET WILL NOT BE OUT
OF THE QUESTION. COOLER AIR CONTINUING TO FILTER INTO WESTERN
WASHINGTON SUNDAY NIGHT WITH THE SNOW LEVEL LOWERING TO NEAR 500
FEET AS THE LOW LEVEL FLOW TRANSITIONS TO OFFSHORE FLOW. THIS WILL
ALSO DRY THE LOWER LEVELS OF THE AIR MASS OUT. WILL STAY WITH THE
LOW SNOW LEVELS/CHANCE POPS FORECAST FOR SUNDAY NIGHT. OFFSHORE FLOW
INCREASING ON MONDAY AS A 1050 MB HIGH BUILDS OVER SOUTHERN BRITISH
COLUMBIA GIVING THE AREA COOL BUT SUNNY DAY. LITTLE CHANGE TO THE
EXTENDED FORECAST THIS MORNING. FELTON

&&

.HYDROLOGY...ONE TO TWO INCHES OF RAIN IS EXPECTED OVER THE OLYMPICS
IN THE NEXT 24 HOURS. THIS WILL NOT BE ENOUGH TO DRIVE THE SKOKOMISH
BACK ABOVE FLOOD STAGE. FLOODING IS NOT EXPECTED THE NEXT 7 DAYS.

&&

.AVIATION...A FRONTAL SYSTEM WILL MOVE THROUGH AREA TODAY WITH
WESTERLY FLOW ALOFT. AIR MASS STABLE AND BECOMING INCREASINGLY MOIST
AT ALL LEVELS.

MID AND HIGH CLOUDS EARLY THIS MORNING WITH LOW CLOUDS AND RAIN
BEGINNING TO REACH THE COAST. LOW CLOUDS AND RAIN WILL SPREAD INLAND
THIS MORNING AS THE FRONT MOVES ONSHORE.

KSEA...MID AND HIGH CLOUDS EARLY THIS MORNING. LOW CLOUDS AND RAIN
WILL DEVELOP MID TO LATE MORNING AND CONTINUE MOST OF THE DAY. LIGHT
WIND BECOMING SOUTH 5-10 KNOTS THIS MORNING. SCHNEIDER

&&

.MARINE...A FRONTAL SYSTEM WILL BRING SMALL CRAFT ADVISORY WINDS TO
MOST WATERS TODAY. THERE WILL ALSO BE WEST SWELL 10-13 FEET OVER THE
COASTAL WATERS.

MODERATE ONSHORE FLOW WILL DEVELOP BEHIND THE FRONT TONIGHT AND
WEDNESDAY WITH HIGH PRESSURE OFFSHORE AND LOWER PRESSURE INLAND.
WEAKER WINDS WILL PREVAIL THURSDAY AND FRIDAY AS ONSHORE FLOW
RELAXES. A FRONT AND SURFACE LOW WILL REACH THE AREA ON SATURDAY.

SOME OF THE HIGHER ASTRONOMICAL HIGH TIDES OF THE YEAR WILL OCCUR
THIS WEEK ALONG WITH SLIGHT TIDAL ANOMALIES. MINOR TIDAL OVERFLOW IS
POSSIBLE EACH DAY FOR THE NEXT FEW DAYS WITH THE BEST AND MOST
WIDESPREAD CHANCES WEDNESDAY MORNING OVER PUGET SOUND AND THE
NORTHERN INLAND WATERS. SCHNEIDER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...

WA...COASTAL FLOOD ADVISORY CENTRAL AND NORTH COAST AND INLAND
     WATERS EXCLUDING THE STRAIT OF JUAN DE FUCA.

PZ...SMALL CRAFT ADVISORY ALL WATERS.
     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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