High Wind Watch 3, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
355 AM PST FRI DEC 12 2008

.SYNOPSIS...LOW PRESSURE IS FORECAST TO EXPLOSIVELY DEEPEN OFFSHORE
THEN MOVE ACROSS WESTERN WASHINGTON THIS AFTERNOON AND EVENING. THIS
LOW WILL BRING STRONG WINDS TO THE COAST. THE LOW IS FORECAST TO
MOVE THROUGH THE CENTRAL SOUND LATE THIS AFTERNOON AND CONTINUE TO
MOVE EAST TONIGHT. RAIN WILL TURN TO SNOW NEAR AND NORTH OF THE LOW
THIS EVENING WITH THE PRECIPITATION TAPERING OFF FROM THE NORTH LATE
TONIGHT AND SATURDAY MORNING. MODIFIED ARCTIC AIR WILL MOVE SOUTH
OVER THE WEEKEND MAKING ALL OF WESTERN WASHINGTON COLD. SNOW SHOWERS
ARE POSSIBLE THIS WEEKEND AS PACIFIC MOISTURE OVERRUNS THE LOW LEVEL
COLD AIR. COLD WEATHER WILL CONTINUE THROUGH NEXT WEEK.

&&

.SHORT TERM...WHERE IS THE LOW GOING TO GO??? THE ANSWER TO THIS
QUESTION WILL BE THE DRIVING FORCE BEHIND THE FORECASTS THIS
MORNING. HARD TO PICK UP THE CURRENT LOCATION ON THE IR SATELLITE
IMAGERY. WATER VAPOR IMAGERY PUTS THE LOW SOMEWHERE NEAR 49N/132W.
THE FORECAST MODELS ARE DIFFERING ON THE TRACK OF THE QUICKLY
DEVELOPING LOW OFFSHORE. THE NAM MODEL RUNS TAKE THE LOW INLAND NEAR
THE OLYMPICS AND TRACK THE LOW NORTH OF SEATTLE AS IT MOVES EAST
TONIGHT. THE GFS SOLUTIONS HAVE A FURTHER SOUTH TRACK WITH THE LOW
TRACKING OVER TO JUST TO THE SOUTH OF SEATTLE IN THE 00Z-06Z
TIMEFRAME. AT THIS POINT IN TIME WITH THE COLD AIR SPILLING OUT
BEHIND THE LOW DIGGING THE TROUGH FURTHER SOUTH AND THE
NORTHWESTERLY WINDS ALOFT BEHIND LOW WHICH WILL HELP FORM A LEE SIDE
LOW NEAR THE OLYMPICS OVER THE CENTRAL SOUND PREFER THE SOUTHERN
TRACK OF THE GFS MODEL RUNS. THIS MORE SOUTHERLY TRACK WILL RESULT
IN...

FOR WIND...HIGH WIND WARNING ONLY UP FOR THE COAST AT THIS POINT.
STILL EXPECTING STRONG NORTHWESTERLY WINDS BEHIND THE LOW TO REACH
THE COAST THIS AFTERNOON. WINDS AHEAD OF THE LOW WILL PICK UP OUT OF
THE SOUTHEAST BUT IT WILL BE THE POST FRONTAL NORTHWESTERLIES THAT
WILL BE THE STRONGEST WINDS ALONG THE COAST TODAY. LATE MORNING INTO
THE AFTERNOON HOURS IS THE TIMING FOR THE WINDS. WITH THE SOUTHERLY
TRACK OF THE LOW HAVE DROPPED THE HIGH WIND WATCH FOR THE STRAIT AND
FOR THE NORTHWESTERLIES COMING OUT OF THE STRAIT OF GEORGIA INTO THE
NORTHERN AREA LATER THIS AFTERNOON INTO THIS EVENING. GALES STILL
POSSIBLE THROUGH THE STRAIT BUT HIGH WINDS TO NOT LOOK LIKELY. A
HIGH WIND WATCH HAS BEEN ISSUED FOR SATURDAY FOR WESTERN WHATCOM AND
SKAGIT COUNTIES AS WELL AS THE SAN JUANS FOR NORTHEASTERLY OUTFLOW
WINDS SATURDAY.

PRECIPITATION...PRECIPITATION WILL BEGIN AS RAIN THIS MORNING ON THE
COAST AND LATE MORNING INTO THE AFTERNOON HOURS FOR THE INTERIOR. AS
THE LOW MOVES INTO THE CENTRAL PUGET SOUND AREA LATE THIS AFTERNOON
THE WINDS NORTH OF THE LOW WILL TURN NORTHERLY. THIS WILL DRIVE COOL
AIR INTO THE INTERIOR WITH THE PRECIPITATION CHANGING OVER FROM RAIN
TO RAIN AND SNOW MIXED THEN SNOW OVER THE NORTHERN SECTIONS OF THE
CWA THIS EVENING. AS THE LOW CONTINUES TO TRACK TO THE EAST THE
PRECIPITATION WILL TAPER OFF FORM THE NORTH LATER THIS EVENING. SO
WHAT WILL HAPPEN IN THE CENTRAL SOUND. WITH THE CURRENT FORECAST
TRACK OF THE LOW SNOW WILL BEGIN OVER ON THE KITSAP PENINSULA LATE
THIS AFTERNOON INTO THE EARLY EVENING HOURS. FOR THE REMAINDER OF
THE AREA THE AIR MASS WILL BE TOO WARM INITIALLY AND PRECIPITATION
WILL STAY IN THE FORM OF RAIN. THE EXCEPTION TO THIS WILL BE WHERE
CONVERGENCE DEVELOPS. THIS WILL INCREASE THE INTENSITY OF THE
PRECIPITATION WHICH WILL DRIVE THE SNOW LEVEL DOWN TO NEAR THE
SURFACE THIS EVENING. WHERE THE CONVERGENCE FORMS IS A TOUGH CALL AT
THIS POINT. THIS WILL NOT BE THE TYPICAL CONVERGENCE ZONE WHERE THE
CONVERGENCE DEVELOPS NEAR KPAE. WITH THE TRACK OF THE LOW
CONVERGENCE COULD DEVELOP OVER THE CENTRAL SOUND THIS EVENING. MODEL
CROSS SECTIONS SHOW THE WINDS ALOFT SWITCHING TO NORTHWESTERLY AFTER
00Z AND REMAINING NORTHWESTERLY THROUGH THE NIGHT. THIS WILL PUSH
COOLER AIR INTO THE CENTRAL SOUND INCREASING THE CHANCES FOR SNOW AS
THE NIGHT WEARS ON. WILL GO AHEAD AND UPGRADE THE WATCH TO A WARNING
FOR CENTRAL SOUND LOCATIONS BUT STILL BE RATHER VAGUE ON THE EXACT
LOCATION OF THE HIGHER SNOW AMOUNTS. EVEN WITH THE CONVERGENCE
LOCATIONS NEAR THE WATER PROBABLY WONT SEE ANY ACCUMULATING SNOW. BY
LATE TONIGHT THE SNOW LEVEL OUTSIDE THE CONVERGENCE WILL BE LOW
ENOUGH FOR THE SHOWERS IN THE HIGHER HILLS TO BE IN THE FORM OF
SNOW. WILL RUN THE WARNING INTO THE MORNING HOURS ON SATURDAY WITH
THE PRECIPITATION DECREASING QUICKLY SATURDAY MORNING.

SOUTH OF THE LOW TRACK THE PRECIPITATION WILL BE IN THE FORM OF RAIN
TONIGHT. AS THE COOLER AIR FILTERS DOWN INTO THE AREA LATE TONIGHT
INTO SATURDAY MORNING THERE IS A CHANCE THE PRECIPITATION COULD
CHANGE OVER TO SNOW SO WILL KEEP A WINTER WEATHER WATCH UP FOR THE
SOUTHWEST INTERIOR...LOWER CHEHALIS VALLEY AND COAST AREAS.

ON SATURDAY THE REALLY COLD AIR STREAMS INTO THE AREA WITH STRONG
NORTHEASTERLY OUTFLOW WINDS IN BELLINGHAM AREA. WITH THESE WINDS THE
POSSIBILITY OF UPSLOPE SNOWS INTO THE NORTHERN SLOPES OF THE
OLYMPICS WILL CONTINUE THROUGHOUT SATURDAY. WITH THE COLDER AIR MASS
SETTLING IN SHOWERS ON SATURDAY WILL MOSTLY BE IN THE FORM OF SNOW.
WITH THE INCREASING OUTFLOW WINDS THE AIR MASS WILL ALSO BEGIN TO
DRY OUT AS WELL. WILL LOWER THE POPS ON SATURDAY.

ANOTHER COLD UPPER LEVEL LOW DROP DOWN OVER WESTERN WASHINGTON FROM
THE NORTH ON SUNDAY GIVING THE AREA ANOTHER ROUND OF SNOW SHOWERS.

.LONG TERM...NOT MUCH CHANGE IN THE EXTENDED MODELS THIS MORNING
WITH COLD AND DRY OFFSHORE FLOW CONTINUING INTO THE LATTER PART OF
NEXT WEEK. BOTH THE GFS AND THE EURO CONTINUE TO SHOW A REINFORCING
ARCTIC BOUNDARY COMING DOWN WED MAYBE GIVING A BRIEF SHOT OF SNOW.
HIGH TEMPERATURES WILL STRUGGLE TO GET ABOVE FREEZING OVER THE
UPCOMING WEEK. FELTON

&&

.AVIATION...FLOW ALOFT HAS BECOME WEST-SOUTHWESTERLY AHEAD OF A
STRONG STORM SYSTEM RAPIDLY DEVELOPING OFFSHORE THIS MORNING. A
DEEPENING SURFACE LOW WILL PUSH A FRONT INTO WESTERN WASHINGTON 21Z
TO 00Z. THE DEEP SURFACE LOW WILL CREATE STRONG LOW LEVEL WINDS THIS
AFTERNOON AND EVENING...ESPECIALLY OVER COASTAL AREAS AND THE
SOUTHERN HALF OF THE WESTERN WASHINGTON INTERIOR. A MODIFIED ARCTIC
FRONT WILL USHER IN NORTHERLY FLOW ON SATURDAY. MVFR CEILINGS WILL
REMAIN WIDESPREAD THROUGH THE FORECAST PERIOD...WITH POSSIBLE IFR
NEAR FRONTAL PASSAGE AS WELL AS CONVERGENCE ACTIVITY THIS EVENING.

KSEA...MVFR CEILINGS ARE EXPECTED TO CONTINUE THIS MORNING...PERHAPS
LIFTING SLIGHTLY TO AROUND OVC025-030 PRIOR TO THE ONSET OF PRECIP.
MVFR IS EXPECTED TO DOMINATE THROUGH MUCH OF THE FORECAST
PERIOD...WITH TEMPO IFR POSSIBLE NEAR FRONTAL PASSAGE 22-00Z. LIGHT
SE SURFACE WINDS WILL BECOME SOUTHERLY LATER THIS MORNING...THEN
RAPIDLY INCREASE AND BECOME RATHER GUSTY BY MID OR LATE AFTERNOON.
BY 21Z...WINDS NEAR 2000 FEET COULD APPROACH 45 KNOTS...AND 60 KNOTS
NEAR 5000 FEET.

&&

.MARINE...A SURFACE LOW IS EXPECTED TO RAPIDLY DEEPEN OVER THE
OFFSHORE WATERS THIS MORNING...THEN STRENGTHEN TO BELOW 990 MB
AS IT MOVES ONTO THE WASHINGTON COAST THIS AFTERNOON. THIS IS
EXPECTED TO PRODUCE STORM FORCE WIND OVER THE COASTAL WATERS...WITH
GALE FORCE EXPECTED OVER MUCH OF THE INLAND WATERS LATER THIS
AFTERNOON AND EVENING. THE LOW AND ASSOCIATED FRONT WILL SHIFT INTO
THE INLAND WATERS THIS AFTERNOON AND EVENING. A COASTAL FLOOD
ADVISORY WILL BE ISSUED FOR MINOR TIDAL OVERFLOW CAUSED BY A
COMBINATION OF LOW PRESSURE AND HIGH TIDES MIDDAY INTO THIS
AFTERNOON. HIGH SURF CONDITIONS ALONG WITH ANOTHER HIGH TIDE MAY
RENEW THE THREAT OF COASTAL FLOODING ON SATURDAY. NORTHERLY FLOW
WILL DEVELOP ON SATURDAY AS THE SURFACE LOW MOVES SHIFTS EAST OF THE
CASCADES AND A MODIFIED ARCTIC BOUNDARY SLIDES SOUTHWARD ACROSS THE
WATERS. 27

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WINTER STORM WATCH FOR THE OLYMPICS AND THE CENTRAL AND
     NORTH CASCADES.
     HIGH WIND WATCH FOR THE CENTRAL AND NORTH COAST...STRAIT
     OF JUAN DE FUCA AREA...SAN JUAN ISLANDS AND WESTERN
     WHATCOM COUNTY.
     COASTAL FLOOD ADVISORY CENTRAL COAST...EAST STRAIT...NORTHWEST
     INTERIOR...AND GREATER PUGET SOUND/HOOD CANAL AREA.

PZ...STORM WARNING IN EFFECT FOR THE COASTAL WATERS.
     GALE WARNING IN EFFECT FOR THE REMAINING WATERS.
     SMALL CRAFT ADVISORY IN EFFECT FOR ROUGH GRAYS HARBOR BAR
     CONDITIONS.

WEATHER.GOV/SEATTLE