Winter Storm Warning 9, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 AM PST THU DEC 14 2006

.SYNOPSIS...A DEEP LOW PRESSURE SYSTEM AND ITS FRONT WILL SPREAD
RAIN ACROSS WESTERN WASHINGTON TODAY...AND PRODUCE DAMAGING WINDS
LATE THIS AFTERNOON THROUGH FRIDAY MORNING AS IT MOVES ACROSS THE
AREA. THE SYSTEM WILL ALSO PRODUCE HEAVY SNOW IN THE MOUNTAINS. A
WEAK UPPER TROUGH WILL BRING COOL AND QUIETER WEATHER THIS WEEKEND
...AND A WEAK UPPER RIDGE WILL BUILD EARLY NEXT WEEK.

&&

.SHORT TERM...WE ARE CURRENTLY IN THE LULL BETWEEN FRONTAL SYSTEMS
...WITH A MINOR UPPER RIDGE BUILDING OVER WRN WA AHEAD OF THE NEXT
MAJOR STORM. A WEAK PUGET SOUND CONVERGENCE ZONE DIED OUT OVERNIGHT
...LEAVING ONLY SPOTTY SHOWERS.

THE CENTER OF THE NEXT SYSTEM UPSTREAM IS NEAR 44N/140W...AND IT IS
ON TRACK TO BECOME A SIGNIFICANT WIND EVENT FOR MUCH OF WRN WA LATE
TODAY THROUGH FRI MORNING -- AS WE HAVE BEEN ADVERTISING. THE STORM
IS IN A GOOD ENVIRONMENT FOR STRONG SURFACE DEVELOPMENT -- IN THE
LEFT EXIT REGION OF A 190 KT JET AND NEAR THE RIGHT ENTRANCE REGION
OF A DOWNSTREAM JET. THE SURFACE LOW -- CURRENTLY AROUND 988 MB --
WILL DEEPEN TO AROUND 972 MB AND PROBABLY MAKE LANDFALL NEAR THE
NORTH TIP OF THE OLYMPIC PENINSULA AROUND MIDNIGHT TONIGHT. IT WILL
MOVE QUICKLY INTO SOUTHWEST BRITISH COLUMBIA LATE TONIGHT...WITH ITS
BENT BACK OCCLUSION SWINGING THROUGH WRN WA.

SATELLITE DATA ALREADY SHOW A FAIRLY LARGE AREA OF 40 KT OR HIGHER
WINDS AHEAD OF AND WITH THE OCCLUSION. I PLAN TO UPGRADE THE WATCH
TO A HIGH WIND WARNING WITH THE MORNING FORECAST PACKAGE. SOUTHERLY
WINDS AHEAD OF THE SURFACE LOW WILL RISE INTO THE 40 TO 50 MPH RANGE
THU EVENING WITH GUSTS TO AROUND 65 MPH. THE STRONGEST WINDS WILL
PROBABLY WITH THE OCCLUSION THU NIGHT...WITH STRONG WESTERLIES
REACHING THE COAST AND SURGING THROUGH THE STRAIT OF JUAN DE FUCA
AND ACROSS THE WHIDBEY ISLAND AREA. THESE WINDS COULD BE AS STRONG
AS 50 TO 60 MPH WITH THE POTENTIAL FOR GUSTS AS HIGH AS 80 TO 90 MPH.

I WILL ISSUE A WINTER STORM WARNING FOR THE CASCADES FOR THIS FRONT
... AS IT WILL PRODUCE ONE TO TWO FEET OF NEW SNOW WITH THE SNOW
LEVEL AROUND 3000 FT. WE WILL ALSO HAVE A CONTINUING FLOOD WARNING
FOR THE SKOKOMISH RIVER.

THE WIND WILL DROP OFF FRI MORNING...AND SHOWERS WILL DECREASE WITH
SOME SUN BREAKS LIKELY FRI AFTERNOON. THE SNOW LEVEL BEHIND THE
FRONT WILL FALL TO AROUND 1000 FT ON FRI...AND FAIRLY STRONG
WESTERLY FLOW WILL KEEP SNOW FALLING IN THE MOUNTAINS. A WEAKENING
SHORTWAVE WILL REACH THE AREA ON SAT. MCDONNAL

&&

.LONG TERM...THE LONGER RANGE MODELS ARE IN GENERAL AGREEMENT THAT
SUN THROUGH WED WILL BE A RELATIVELY QUIET PERIOD. AN UPPER RIDGE
OVER THE AREA SUN AND MON WILL PROBABLY GIVE WAY TO A FRONTAL SYSTEM
AROUND TUE AND THEN REBOUND ON WED. MCDONNAL

&&

.AVIATION...DELAYED.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...

1. HIGH WIND WARNING FOR MOST OF WESTERN WASHINGTON (INCLUDES THE
OLYMPICS BUT NOT THE CASCADES) THIS AFTERNOON THROUGH FRI MORNING.
2. HEAVY SNOW WARNING FOR THE CASCADES NOON TODAY THROUGH NOON
FRI.
3. STORM WARNING ALL WATERS.
4. HIGH SURF ADVISORY AND COASTAL FLOOD WATCH IN EFFECT FOR THE
WASHINGTON COAST.