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000
FXUS66 KSEW 100455
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 PM PST MON DEC 9 2013

.SYNOPSIS...A WEAK WEATHER SYSTEM WILL PRODUCE OCCASIONAL LIGHT SNOW
TONIGHT AND TUESDAY MORNING. BY TUESDAY AFTERNOON THERE WILL BE RAIN
IN THE MIX AS THE AIR MASS WARMS. TEMPERATURES WILL RISE TO NEAR
NORMAL WEDNESDAY. A PACIFIC FRONT WILL BRING MORE TYPICAL RAIN AND
WIND THURSDAY...FOLLOWED BY ANOTHER PACIFIC FRONT OVER THE WEEKEND.

&&

.SHORT TERM...AN UPPER LEVEL RIDGE REMAINS OFFSHORE ALONG 140W
THIS EVENING...WITH NORTHWEST FLOW ALOFT OVER THE PACIFIC NORTHWEST.
A VERY WEAK UPPER SHORTWAVE IN THE NORTHWEST FLOW MOVED ACROSS
WESTERN WASHINGTON THIS AFTERNOON...AND A SECOND ONE IS MOVING
TOWARD THE FORECAST AREA FROM BRITISH COLUMBIA THIS EVENING. THE AIR
MASS IS FAIRLY MOIST...ESPECIALLY THE LOWER 8000 FT...AND THE
RELATIVELY WARM PACIFIC MOISTURE OVERRUNNING THE COLD AIR MASS OVER
WESTERN WASHINGTON IS PRODUCING SPOTTY LIGHT SNOW FLURRIES.

THE SHORTWAVE TO OUR NORTH WILL MOVE INTO WESTERN WASHINGTON
TONIGHT...AND PRECIPITATION SHOULD BECOME MORE WIDESPREAD LATER
TONIGHT AND TUESDAY MORNING. PRECIPITATION AMOUNTS WILL BE LIGHT...
AND IN FACT THE QPF IN THE 00Z TUE MODEL RUNS IS A BIT LESS THAN IT
WAS IN THE 12Z MON RUNS. WE CAN EXPECT 0.05 TO 0.15 INCH FOR MOST OF
THE LOWLANDS TONIGHT THROUGH TUESDAY MORNING...EXCEPT AS NOTED IN
THE PARAGRAPH BELOW. GENERALLY THIS WILL FALL AS LIGHT SNOW WITH
ACCUMULATIONS UP TO AN INCH. THE IMMEDIATE COAST SHOULD GET LESS AS
PRECIPITATION WILL TURN TO RAIN THERE OVERNIGHT.

PRECIPITATION WILL BE A LITTLE HEAVIER OVER THE EAST PUGET SOUND
LOWLANDS NEAR THE CASCADES -- IE PLACES LIKE BUCKLEY...ENUMCLAW...
NORTH BEND...GOLD BAR...SULTAN...ETC. AMOUNTS THERE WILL BE MAINLY
0.10 TO 0.25 INCH WITH SNOW ACCUMULATIONS OF 1 TO 3 INCHES IN SOME
AREAS. A WINTER WEATHER ADVISORY FOR SNOW IS IN EFFECT FOR THE EAST
PUGET SOUND LOWLANDS THROUGH NOON TUESDAY.

THE SHORTWAVE WILL MOVE SOUTHEAST OF THE FORECAST AREA TUESDAY
AFTERNOON. PRECIPITATION WILL TAPER OFF AND TEMPERATURES WILL BE IN
THE MID TO UPPER 30S...SO NO ADDITIONAL SNOW ACCUMULATION IS
EXPECTED AFTER MIDDAY TUESDAY.

THE OFFSHORE UPPER RIDGE WILL APPROACH THE PACIFIC NORTHWEST TUESDAY
NIGHT AND MOVE INLAND WEDNESDAY. PRECIPITATION WILL BE LIGHT AND
SPOTTY AT BEST...AND ANY PRECIPITATION THAT DOES FALL WILL BE RAIN.
HIGHS WEDNESDAY WILL BE NEAR SEASONAL NORMALS AGAIN IN THE LOWER TO
MID 40S.

THE UPPER RIDGE WILL MOVE EAST OF THE CASCADES WEDNESDAY NIGHT...AND
A PACIFIC FRONTAL SYSTEM WILL MOVE THROUGH WESTERN WASHINGTON
THURSDAY AND THURSDAY NIGHT. IT DOES NOT LOOK LIKE AN ESPECIALLY
STRONG FRONT...BUT IT SHOULD BRING MEASURABLE RAIN TO ALL OF THE
LOWLANDS. IT WILL PROBABLY BRING ADVISORY LEVEL SNOW AMOUNTS TO THE
MOUNTAINS WITH THE SNOW LEVEL 2500 TO 3500 FT.   MCDONNAL

.LONG TERM...HERE IS THE LONG TERM SECTION FROM THE AFTERNOON
FORECAST DISCUSSION -- BOTH THE EURO AND GFS HAVE SLOWED THE
PROGRESS OF THE NEXT SYSTEM AND WEAKENED IT CONSIDERABLY. HAVE
DELAYED THE ONSET OF LIKELY POPS TO SATURDAY NIGHT AND SUNDAY.
SHOWERS FOLLOW MONDAY. THERE IS NO HEAVY PRECIPITATION OR SNOW IN
THE EXTENDED FORECAST. HIGHS WILL BE IN THE MID 40S WITH LOWS 35-40.
BURKE

&&

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

&&

.AVIATION...NW FLOW ALOFT. AMS STABLE. WEAK WARM FRONT GIVING CLOUDY
SKIES AND A FEW FLURRIES WHICH SHOULD INCREASE OVERNIGHT. THE UW
WRFGFS HAS PRECIP DEVELOPING LATE TONIGHT OVER THE NW INTERIOR FROM
ABOUT US2 NORTH SO THOSE AREAS COULD SEE AN INCH OF SNOW BUT
ELSEWHERE JUST A SKIFF IS A BETTER BET. THERE DOES NOT SEEM TO BE
MUCH MOISTURE WITH THIS RATHER WEAK WEATHER SYSTEM SO THE CLOUDS MAY
BREAK UP LATE TUESDAY WITH SOME CLEARING. IN FACT...THERE IS AN
UPPER RIDGE JUST OFFSHORE AND THAT WILL SHIFT EAST OVER THE PACNW
WED SO LATE TUE AND WED MAY SEE SOME CLEARING AND LIGHT OFFSHORE
FLOW.

.KSEA...CLOUDY SKIES THROUGH TUESDAY MORNING AND A FEW FLURRIES
POSSIBLE. I DON`T SHOW ANY CLEARING IN THE TAF YET BUT LATE TUESDAY
AN UPPER RIDGE AND LIGHT OFFSHORE FLOW WILL SHIFT OVER THE AREA AND
AT LEAST PARTIAL CLEARING SEEMS A GOOD BET TUE NIGHT.

&&

.MARINE...LIGHT PRESSURE GRADIENTS AS A WEAK WEATHER SYSTEM
DISSIPATES OVER THE AREA TONIGHT AND TUE. LIGHT OFFSHORE FLOW WILL
DEVELOP TUE NIGHT AND WED WITH HIGH PRESSURE INLAND AND LOW PRESSURE
OFFSHORE. THEN A PRETTY DECENT FRONT WILL ARRIVE THURSDAY.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WINTER WEATHER ADVISORY FOR EAST PUGET SOUND LOWLANDS NEAR THE
     CASCADES TONIGHT THROUGH TUESDAY MORNING.
PZ...NONE.

&&

$$

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