Winter Storm Watch 17, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
330 PM PST MON DEC 3 2012

.SYNOPSIS...WIDESPREAD RAIN AND WINDY CONDITIONS WILL RESUME TONIGHT
AND TUESDAY AS ANOTHER STRONG PACIFIC FRONTAL SYSTEM MOVES ONSHORE.
COOLER AND MORE UNSTABLE AIR WILL FOLLOW FOR A SHOWERY WEATHER
PATTERN STARTING TUESDAY AFTERNOON AND LASTING THROUGH WEDNESDAY. A
WEAKER SYSTEM WILL ARRIVE THURSDAY...THEN COOLER AND SOMEWHAT DRIER
CONDITIONS WILL PREVAIL INTO THE WEEKEND.

&&

.SHORT TERM...RAIN AT TIMES HAS BEEN OCCURRING TODAY BUT AMOUNTS SO
FAR ARE UNIMPRESSIVE. THAT IS LIKELY TO CHANGE TONIGHT AS A STRONG
SYSTEM MOVES THROUGH THE AREA...BRINGING HEAVY RAIN TO THE COAST AND
OLYMPICS AND WINDY CONDITIONS TO THE COAST AND NORTH INTERIOR. WILL
ISSUE A WIND ADVISORY FOR THE COAST AND NORTH INTERIOR FOR TONIGHT
AND TUESDAY MORNING...LOOKING FOR WIND JUST BELOW WARNING CRITERIA
IN THOSE PLACES.

RAINFALL IS FORECAST TO BE 2-4 INCHES OVER THE OLYMPICS WITH LESS
ELSEWHERE...THOUGH THERE WILL BE SOME BULLSEYES IN THE CASCADES AND
ALSO THE WILLAPA HILLS. THE SNOW LEVEL WHICH IS CURRENTLY AROUND
4000 FEET WILL BRIEFLY RISE TO 7000 FEET TUESDAY MORNING...BUT THEN
FALL BELOW 4000 FEET TUESDAY NIGHT. THERE IS SOME QUESTION ABOUT
WHERE EXACTLY THE RAIN/SNOW LINE WILL BE. HIGHER ELEVATIONS MAY GET
HEAVY SNOW WHILE THE MAIN HIGHWAY PASSES MAY GET A MIX OF RAIN AND
SNOW WITH PERHAPS A LITTLE FREEZING RAIN THROWN IN FOR GOOD MEASURE.
WILL ISSUE A WINTER STORM WATCH FOR THE CASCADES AND OLYMPICS TO
COVER THE POSSIBILITY OF HEAVY SNOW FROM TUESDAY MORNING THROUGH
TUESDAY NIGHT.

WEDNESDAY CURRENTLY LOOKS LIKE THE QUIETEST DAY. ZONAL FLOW ALOFT
WILL SHIELD THE SEATTLE METRO AREA BUT THERE WILL BE SCATTERED
SHOWERS ELSEWHERE. THE MOUNTAINS WILL GET MORE SNOW BUT AMOUNTS LOOK
LESS THAN IMPRESSIVE.

MAIN CHANGE TO THE SHORT TERM WAS TO ACCOUNT FOR WHAT APPEARS TO BE
ANOTHER ORGANIZED SYSTEM ARRIVING ON WEDNESDAY NIGHT OR THURSDAY.
HAVE INCREASED POPS AND GENERALLY MADE THE FORECAST WETTER. BURKE

.LONG TERM...AFTER THURSDAY THE UPPER FLOW TURNS MORE NORTHWESTERLY
WHICH WILL BRING COOLER AND SOMEWHAT DRIER AIR INTO THE REGION.
TEMPERATURES WILL FALL. THE MODELS CONTINUE TO RIPPLE SHORT WAVES
THROUGH THE FLOW. HAVE KEPT CHANCE OR BETTER POPS IN EVERY PERIOD
THOUGH THERE ARE LIKELY TO BE SOME BREAKS. EVEN HAVE PARTLY SUNNY IN
THE FORECAST THIS WEEKEND. HOWEVER HIGHS WILL BE AROUND 40 AND LOWS
COULD FALL BELOW FREEZING. HAVE NOT INDICATED SNOW IN ANY ZONES BUT
THE GRIDS HAVE SNOW PEPPERING THE HIGHER HILLS SUCH AS THE CHUCKANUT
RANGE AND THE NORTHERN FOOTHILLS OF THE OLYMPICS. BURKE

&&

.HYDROLOGY...THE SKOKOMISH RIVER FELL SLIGHTLY TODAY BUT WILL RISE
SOMEWHAT TUESDAY IN RESPONSE TO THE RAIN TONIGHT. IT WILL REMAIN
ABOVE FLOOD STAGE THROUGH WEDNESDAY AT LEAST.

A FLOOD WARNING IS IN EFFECT FOR THE REACH OF THE CHEHALIS RIVER
NEAR GRAND MOUND...WITH A WATCH IN EFFECT FOR OTHER REACHES. GIVEN
HOW VIGOROUSLY THE CHEHALIS RIVER RESPONDED TO WHAT WAS NOT
PARTICULARLY HEAVY RAIN LAST NIGHT...IT SEEMS REASONABLE TO ASSUME
THAT THE GROUND IN THAT BASIN IS SATURATED FROM THE PAST SEVERAL
DAYS OF RAIN. THAT MEANS THE RAIN TONIGHT...WHICH ACTUALLY WILL BE
HEAVY AT TIMES...WILL PROBABLY RUN RIGHT OFF INTO THE RIVER. SO THE
CHEHALIS RIVER SEEMS LIKELY TO FLOOD...AT LEAST ALONG SOME REACHES.

OTHER RIVERS...NOTABLY THOSE FLOWING OFF THE CASCADES...ARE NOT
LIKELY TO FLOOD. PRECIPITATION IN THE CASCADES HAS MOSTLY BEEN IN
THE FORM OF SNOW OVER THE LAST SEVERAL DAYS. THERE WILL BE A 12 TO
18 HOUR WARMUP AS THE INCOMING SYSTEM PASSES...AND RAIN WILL BE
HEAVY IN SOME PLACES...BUT SO FAR THE CASCADE RIVERS ARE FORECAST TO
REMAIN WELL BELOW FLOOD STAGE. A COUPLE OF THE FLASHIER RIVERS SUCH
AS THE PUYALLUP NEAR ORTING AND THE TOLT NEAR CARNATION BEAR SOME
WATCHING. BURKE

&&

.AVIATION...A DEEP UPPER LEVEL LOW WILL SPIN OVER THE NE PAC TONIGHT
WITH MOIST WESTERLY FLOW ACROSS WESTERN WA. EXPECT RAIN AT TIMES
THROUGH TUES MORNING AS OUR NEXT PACIFIC FRONTAL SYSTEM MOVES
INLAND. CIGS WILL LIKELY FALL IN MVFR TO LOW-END VFR RANGE /NEAR
3000 FT/. GUSTY WINDS ARE ALSO ANTICIPATED WITH SOUTH WINDS
INCREASING IN THE INTERIOR LATE TUE MORNING. SHOWERS WILL TAPER DOWN
TUE NIGHT /MAINLY AFFECTING THE CASCADES/ AS THIS SYSTEM EXITS. 33

KSEA...EXPECT RAIN AT TIMES TONIGHT WITH CIGS LOWERING TO MVFR
RANGE. SURFACE WINDS WILL REMAIN SOUTHERLY...INCREASING TUE MORNING.
33

&&

.MARINE...SOUTHERLY FLOW WILL INCREASE TONIGHT AS ANOTHER STRONG
PACIFIC FRONTAL SYSTEM MOVES INLAND. GALE WARNINGS ARE IN EFFECT FOR
THE COASTAL WATERS...ENTRANCES TO THE STRAIT AND THE NORTH INTERIOR
WATERS. EXPECT GALES TO LAST THROUGH TUE MORNING. ELSEWHERE WINDS
WILL BE IN SMALL CRAFT ADVISORY RANGE WITH WINDS BECOMING SW/W TUE
AFTERNOON. ONSHORE FLOW WILL PREVAIL TUE NIGHT THROUGH WED FOR A
GENERALLY QUIET PERIOD. A WEAK SURFACE TROUGH WILL THEN SHIFT INLAND
ON THURSDAY...FOLLOWED BY A COLD FRONT ON FRIDAY. 33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WIND ADVISORY COAST AND NORTH INTERIOR TONIGHT AND TUESDAY
     MORNING.
     WINTER STORM WATCH CASCADES AND OLYMPICS TUESDAY AFTERNOON
     THROUGH TUESDAY NIGHT.

PZ...GALE WARNING COASTAL WATERS...ENTRANCES TO THE STRAIT OF JUAN
     DE FUCA...AND THE NORTH INTERIOR WATERS.
     SMALL CRAFT ADVISORY CENTRAL STRAIT...ADMIRALTY INLET...PUGET
     SOUND AND HOOD CANAL.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.

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