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000
FXUS66 KSEW 011752
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
950 AM PST SUN DEC 1 2013

.SYNOPSIS...IT WILL BE WINDY AND WET THROUGH TONIGHT AS A STRONG
FRONTAL SYSTEM APPROACHES THE AREA FROM THE NORTHWEST. THE FRONT
WILL BRING MUCH COOLER AIR ON MONDAY WITH SNOW LEVELS DROPPING TO
AROUND 500 FEET IN THE INTERIOR DURING THE MORNING. DRIER AND MUCH
COLDER AIR WILL MOVE INTO THE AREA FROM THE INTERIOR OF CANADA
MONDAY NIGHT THROUGH THURSDAY. CLOUDS WILL INCREASE LATE THIS WEEK
AND THERE IS A CHANCE OF A LITTLE PRECIPITATION.

&&

.SHORT TERM...ON THE LARGER SCALE...MODELS REMAIN CONSISTENT THROUGH
ABOUT THURSDAY SHOWING A DEEP UPPER TROUGH IN THE GULF OF ALASKA
PASSING SOUTHEAST ACROSS THE AREA ON MONDAY FOLLOWED BY DRY AND COLD
NORTHERLY FLOW MONDAY NIGHT THROUGH ABOUT THURSDAY. THE FRONT
ASSOCIATED WITH THE SYSTEM MOVING IN FROM THE NORTHWEST HAS
ENTRAINED QUITE A BIT OF TROPICAL MOISTURE FROM A LOW NW OF
HAWAII...BUT THE MOISTURE IS DECREASING ON ITS LONG TRIP AROUND THE
RIDGE WEST OF CENTRAL CALIFORNIA AND THE FRONT APPEARS TO BE MOVING
IN FASTER THAN PREVIOUSLY EXPECTED.

THE REAL ISSUES TODAY CONCERN THE FASTER TIMING OF THE UPPER LOW.
THIS CAUSES MOUNTAIN PRECIPITATION THROUGH THIS EVENING TO STILL BE
HEAVY...BUT TO BE A QUICKER SHOT THAN PREVIOUSLY EXPECTED. THIS MAY
REDUCE THE FLOODING POTENTIAL SOMEWHAT FOR RIVERS NORTH OF ABOUT
PIERCE COUNTY LATER THIS AFTERNOON THROUGH EARLY MONDAY. BUT FLOOD
WATCHES WILL BE MAINTAINED FOR THE INTERIOR AREAS FROM SNOHOMISH
COUNTY SOUTHWARD...INCLUDING MASON COUNTY AT THIS TIME.

WITH THE FASTER TIMING...THE 12Z NAM AND GFS SOLUTIONS BRING THE
GREATEST THREAT OF WET SNOW TO HILLS ABOVE ABOUT 500 FEET IN
SNOHOMISH AND KING COUNTIES DURING THE MORNING HOURS. WOULD NOT BE
SURPRISED TO SEE A COUPLE INCH ACCUMULATION WITH A CONVERGENCE ZONE
AT FAVORED PLACES LIKE EVERETT AND ON HILLS EAST OF I-405. BUT
TEMPERATURES WILL BE ABOVE FREEZING WITH ANY SNOW THAT FALLS...SO
IMPACTS ON THE ROADWAYS WILL BE BRIEF AND MINIMAL AND ANYTHING THAT
FALLS WILL LIKELY MELT OFF IN A COUPLE OF HOURS.

FRASER OUTFLOW STARTS NOW IN THE AFTERNOON. FORECAST WIND SPEEDS
FROM THE SAN JUANS NORTHEASTWARD WERE INCREASED GIVEN THE -16MB PRES
GRADIENTS FROM BELLINGHAM TO WILLIAMS LAKE STARTING LATE IN THE
AFTERNOON AND CONTINUING THROUGH ABOUT TUESDAY. A WIND ADVISORY MAY
BE REQUIRED FOR THESE AREAS LATER.

IT WILL GET COLD STARTING MONDAY NIGHT AND CONTINUING THROUGH
WEDNESDAY. WHILE 850 MB TEMPERATURES ONLY FALL TO -7 TO -9C WITH
THIS COLD SPELL IN THE LATEST DETERMINISTIC MODEL SOLUTIONS...THE
GFS REMAINS ON THE WARM SIDE OF THE ENSEMBLE CLUSTER AND WE WILL
STILL GET A GOOD DEAL OF COLD AIR FROM ABOUT 5000 FT DOWNWARD FROM
THE NE. LOWS WILL FALL TO 15-25 WITH HIGHS STRUGGLING TO HIT
FREEZING TUE-THU.

FORECASTS WERE UPDATED TO REFLECT TIMING SHOWN BY LATEST MODEL
SOLUTIONS AND SATELLITE IMAGERY. ALBRECHT

.LONG TERM...FROM THE PREVIOUS LONG TERM SOLUTION...DRY AND COLD
CONDITIONS CONTINUE THROUGH MID-WEEK. APPROACHING THE
WEEKEND...MODELS ARE IN DISAGREEMENT AS TO WHEN NEXT CHANCE OF
PRECIP MAKES ITS WAY TO THE AREA. 00Z GFS REMAINS DRY FOR THE ENTIRE
WEEKEND WHILE THE 00Z ECMWF BRINGS IN A WEAK SYSTEM THAT MIGHT BRING
SLIGHT CHANCE TO CHANCE POPS TO THE FORECAST. INHERITED FORECAST
SEEMED TO REALLY LATCH ON TO THE ECMWF SOLUTION...BUT WITH SUCH A
WIDE DISCREPANCY BETWEEN THE TWO...FELT IT BEST TO PARE BACK A BIT
UNTIL SOME FORM OF CONSENSUS BEGINS TO EMERGE. PRECIP OR
NOT...CONDITIONS WILL REMAIN COLD...WITH ONLY SLIGHT WARMING
EXPECTED. SMR

&&

.HYDROLOGY...THE MOISTURE PLUME APPROACHING FROM THE WEST HAS LOST
SOME OF ITS PUNCH WITH TPW VALUES NOW ONLY AROUND 1.25 INCHES AND
THE PLUME SAGGING A BIT FASTER TO THE SOUTH. THIS MAY LIMIT THE
HEAVY RAINFALL TO A SHORTER TIME PERIOD TODAY THROUGH EARLY THIS
EVENING AND TO AREAS FROM ABOUT PIERCE COUNTY SOUTHWARD. SNOW LEVELS
AROUND 5000-6000 FEET WILL LOWER TO BELOW 500 FEET BY EARLY MONDAY
NORTH PIERCE COUNTY. RAINFALL AMOUNTS ARE EXPECTED TO BE A BIT LESS
NOW...ON THE ORDER OF 2 TO 5 INCHES WITH AN ISOLATED 6 INCH AMOUNT
AROUND MT RAINIER. THE THREAT OF FLOODING ON KING AND SNOHOMISH
COUNTY RIVERS AS DIMINISHED SOMEWHAT.

THE FLOOD WATCH WILL REMAIN IN EFFECT FOR SNOHOMISH...KING...
PIERCE...THURSTON...LEWIS AND MASON COUNTIES BEGINNING THIS
AFTERNOON AND CONTINUING TO NOON MONDAY.

ONCE THE SNOW LEVELS LOWER AND WATER IN RIVERS MOVE DOWNSTREAM...
THE THREAT OF ADDITIONAL FLOODING WILL COME TO AN END QUICKLY
TUESDAY WITH A DRY AND COLD AIR MASS MOVING INTO THE REGION. ALBRECHT

&&

.AVIATION...STRONG WEST-NORTHWEST FLOW ALOFT OVER WESTERN WASHINGTON
TODAY. AIR MASS MOIST UP TO 12000 FEET AND STABLE.

CEILINGS BELOW 1000 FEET OVER MOST OF THE AREA THIS MORNING WITH
LOCAL VISIBILITIES 2 TO 4 SM IN RA. A RAIN SHADOW IS BEGINNING TO
FORM ON THE EAST SIDE OF THE OLYMPICS AND WILL SPREAD OVER THE
CENTRAL SOUND LATER THIS MORNING INTO THE AFTERNOON HOURS. AS THIS
OCCURS CEILINGS WILL IMPROVE UP INTO THE 1000 TO 2000 FOOT RANGE
LATER THIS MORNING AND TO 2000 TO 3000 FEET BY LATE THIS AFTERNOON.
THE EXCEPTION TO THIS WILL BE IN THE CONVERGENCE ZONE NEAR KPAE THIS
AFTERNOON. FOR THE SOUTHWEST INTERIOR AND COAST IFR CONDITIONS WILL
CONTINUE INTO THE AFTERNOON HOURS. OVER THE NORTH SOUND CEILINGS
WILL ALSO IMPROVE THIS AFTERNOON UP INTO THE 2000-3000 FOOT RANGE.

KSEA...CEILINGS BELOW 1000 FEET IMPROVING THIS MORNING TO 1000 TO
2000 FEET AND TO 2000 TO 3000 FEET BY LATE AFTERNOON. VISIBILITIES 1
TO 3 SM AT TIMES THIS MORNING IN RAIN AND FOG. SOUTHERLY WIND 10 TO
15 KNOTS. FELTON

&&

.MARINE...710AM UPDATE...UIL-BLI WAS 4.8MB AT 7AM WITH RACE ROCKS
WSW 35KTS SO CHANGED THE GALE WARNING START TIME FROM 10AM TO RIGHT
AWAY. PREVIOUS DISCUSSION FOLLOWS...A STRONG COLD FRONT WILL MOVE
THROUGH THE AREA TODAY.  A 998 MB SURFACE LOW WILL MOVE ACROSS
SOUTHERN BRITISH COLUMBIA TONIGHT. GALE WARNINGS FOR THE COASTAL
WATERS REMAIN IN EFFECT UNTIL NOON TODAY. CONFIDENCE IS HIGH THAT
SOLID WESTERLY GALE WILL DEVELOP IN THE CENTRAL AND EASTERN STRAIT
LATER TODAY AND A GALE WARNING REMAINS IN EFFECT THERE AS WELL.
SMALL CRAFT ADVISORY WINDS ARE EXPECTED OVER THE REMAINDER OF THE
WATERS.

A MODIFIED ARCTIC FRONT WILL MOVE THROUGH WESTERN WASHINGTON FROM
THE NORTH MONDAY...WITH STRONG NORTHEAST FRASER OUTFLOW WINDS
DEVELOPING LATE MONDAY AND CONTINUING THROUGH TUESDAY. THESE WILL
PROBABLY REACH GALE FORCE OVER THE NORTHERN INLAND WATERS AND
POSSIBLY THE STRAIT. THE NORTHEASTERLY GRADIENTS WILL EASE IN THE
MIDDLE OF THE WEEK. FELTON

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WATCH NOON TODAY THROUGH NOON MONDAY FOR
     SNOHOMISH...KING...PIERCE...THURSTON...LEWIS AND MASON
     COUNTIES.
PZ...GALE WARNING COASTAL WATERS.
     GALE WARNING CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA.
     SMALL CRAFT ADVISORY REMAINING WATERS.
     SMALL CRAFT ADVISORY GRAYS HARBOR FOR ROUGH BAR CONDITIONS.

&&

$$

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