Heavy Snow in Washington, March 14 to 15, 2012

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 AM PDT WED MAR 14 2012

.SYNOPSIS...A VIGOROUS FRONTAL SYSTEM WILL MOVE THROUGH THE AREA
TODAY...FOLLOWED QUICKLY BY ANOTHER WEATHER SYSTEM TONIGHT AND
THURSDAY...FOR WET AND OCCASIONALLY WINDY WEATHER AND HEAVY SNOW IN
THE MOUNTAINS. SHOWERY WEATHER WILL CONTINUE ON FRIDAY. THE WEATHER
PATTERN WILL REMAIN ACTIVE ON SATURDAY AS ANOTHER STRONG SURFACE LOW
MOVES INLAND.

&&

.SHORT TERM...THE UPPER TROUGH THAT MOVED THROUGH WESTERN WASHINGTON
TUESDAY IS WELL EAST OF THE REGION NOW...AND THE NEXT FRONTAL SYSTEM
IS APPROACHING FROM THE OFFSHORE WATERS. SO WE HAVE A BRIEF LULL IN
THE ACTIVE WEATHER PATTERN EARLY THIS MORNING...WITH MAINLY CLOUDY
SKIES AND SPOTTY LIGHT PRECIPITATION. A COLD AIR MASS REMAINS OVER
THE FORECAST AREA WITH TEMPERATURES IN THE 30S AND THE SNOW LEVEL
WITHIN A FEW HUNDRED FEET OF SEA LEVEL.

PRECIPITATION WILL SPREAD ACROSS WESTERN WASHINGTON THIS MORNING...
AND THE SURFACE FRONT WILL SWING NORTHEAST ACROSS THE AREA THIS
AFTERNOON. FAIRLY STRONG SOUTHEAST PRESSURE GRADIENTS ACROSS THE
REGION SHOULD PRODUCE WIND ADVISORY WINDS (IE SUSTAINED UP TO 35 MPH
AND GUSTS UP TO 55 MPH) IN THE COASTAL AND NORTHWEST INTERIOR ZONES.
A WIND ADVISORY IS ALREADY IN EFFECT TODAY FOR THOSE AREA. IT WILL
BE BREEZY TO WINDY ELSEWHERE.

THIS SYSTEM WILL REPLACE THE COLD AIR MASS WITH A MILDER ONE...
HOWEVER AS PRECIPITATION STARTS THIS MORNING IT WILL STILL BE COLD
ENOUGH FOR SNOW IN THE WESTERN WASHINGTON LOWLANDS. WITH ONE MAIN
EXCEPTION...ACCUMULATIONS SHOULD BE LIMITED TO AROUND 1 INCH AS THE
COLD LOW LEVEL AIR IS QUICKLY SCOURED AWAY. THE EXCEPTION IS THE
AREA ALONG THE EAST SIDE OF THE OLYMPIC MOUNTAINS...IN OTHER WORDS
THE HOOD CANAL AREA ZONE. COLD AIR IS NATURALLY TRAPPED THERE DURING
LOW LEVEL EASTERLY FLOW AHEAD OF A FRONT...AND SIGNIFICANT
PRECIPITATION AMOUNTS WILL OCCUR WHILE IT IS STILL THERE. A WINTER
STORM WARNING IS IN EFFECT THERE FOR ACCUMULATIONS OF 2 TO 6 INCHES
THIS MORNING.

ANOTHER STRONG FRONTAL SYSTEM...WHICH IS BEGINNING TO DEVELOP OUT
NEAR 155W...WILL MOVE THROUGH WESTERN WASHINGTON TONIGHT AND
THURSDAY. THIS FEATURE...ASSOCIATED WITH A STRONG WESTERLY JET...
WILL BRING ANOTHER ROUND OF WINDY CONDITIONS ESPECIALLY TO THE COAST
AND NORTHWEST INTERIOR. THE DEVELOPING SURFACE LOW IS FORECAST TO
CURL NORTHEAST OUTSIDE OF 130W INTO HAIDA GWAII -- RECENTLY KNOWN AS
THE QUEEN CHARLOTTES -- WHICH SUGGESTS HIGH WIND IS UNLIKELY FOR
WESTERN WASHINGTON. SO WE WILL STAY WITH THE IDEA OF ANOTHER WIND
ADVISORY LEVEL EVENT.

PRECIPITATION WITH THIS SYSTEM WILL ALSO BE SUBSTANTIAL FOR BOTH THE
LOWLANDS AND THE MOUNTAINS. THE TWO SYSTEMS COMBINED WILL PRODUCE
STORM TOTAL PRECIPITATION AMOUNTS OF 1 TO 2.5 INCHES FOR THE
COASTAL...SOUTHWEST WASHINGTON...AND HOOD CANAL AREA ZONES AND
ROUGHLY 0.5 TO 1.5 INCHES ELSEWHERE IN THE INTERIOR LOWLANDS. THE
MOUNTAINS WILL GET 2 TO 5 INCHES OF PRECIPITATION AS THE SNOW LEVEL
RISES GRADUALLY TO AROUND 4500 FT ON THURSDAY. A WINTER STORM
WARNING IS IN EFFECT FOR THE MOUNTAINS ALREADY.

A COOL AND UNSTABLE AIR MASS WILL FOLLOW THE FRONT FOR THURSDAY
NIGHT FOR WIDESPREAD SHOWERS. A SHOWERY REGIME WILL CONTINUE FRIDAY
AHEAD OF ANOTHER DEVELOP SYSTEM OFFSHORE. THE SNOW LEVEL WILL FALL
TO AROUND 2500 FT THURSDAY NIGHT AND FRIDAY.   MCDONNAL

.LONG TERM...A FEW DAYS AGO IT LOOKED LIKE SATURDAY WOULD BE A COOL
BUT RATHER QUIET DAY WITH A MIX OF LIGHT SHOWERS AND SOME SUN
BREAKS. THE FORECAST HAS CHANGED THOUGH...AND IT COULD CHANGE MORE
OVER THE NEXT DAY OR SO.

ON FRIDAY THERE WILL BE ANOTHER DEEP COLD UPPER TROUGH CENTERED
OFFSHORE ALONG 140W...AND A VERY STRONG NORTHWEST JET OF 180 KT OR
SO WILL BEGIN TO INTERACT WITH IT. ALL THE MODELS ARE FORECASTING
THE DEVELOPMENT OF ANOTHER FRONTAL SYSTEM...BUT THEY ARE HAVING LOTS
OF DIFFICULTY WITH STRENGTH...TIMING AND TRACK. SOME RUNS OF THE
EUROPEAN MODEL HAVE INDICATED A WINDSTORM SCENARIO. I DO NOT FEEL
ENOUGH CONFIDENCE TO MAKE LONG TERM FORECAST CHANGE AT THIS
TIME...BUT IT WILL BE INTERESTING TO SEE HOW THIS DEVELOPS.

SUNDAY AND MAYBE MONDAY WILL PROBABLY BE QUIETER DAYS BEFORE ANOTHER
STRONG FRONTAL SYSTEM ARRIVES TUESDAY...OR MAYBE IT WILL ARRIVE
MONDAY. THE MODELS ARE TRENDING TOWARD THE IDEA OF A BRIEFER AND
BRIEFER BREAK LATE THIS WEEKEND AND EARLY NEXT WEEK BEFORE A VERY
ACTIVE WEATHER PATTERN RESUMES NEXT WEEK.   MCDONNAL

&&

.HYDROLOGY...AS DISCUSSED ABOVE THE PRECIPITATION FROM THE STORM
TODAY AND THE STORM TONIGHT AND THURSDAY WILL BE SUBSTANTIAL...WITH
GENERALLY 2 TO 5 INCHES IN THE MOUNTAINS DURING A 48-HOUR PERIOD.
THE HEAVIEST AMOUNTS WILL OCCUR OVER THE SOUTH SLOPES OF THE
OLYMPICS...AND THE MEAN AREAL PRECIPITATION OVER THE SKOKOMISH RIVER
BASIN WILL LIKELY BE AROUND 3 INCHES. THE SNOW LEVEL WILL GRADUALLY
RISE TO AROUND 4500 FT THURSDAY.

EVEN WITH RELATIVELY LOW SNOW LEVELS DURING MOST OF THE EVENT...
THERE IS SOMETHING LIKE A 20 PERCENT CHANCE THAT THE UNIQUELY
FLOOD-PRONE SKOKOMISH RIVER WILL HAVE MINOR FLOODING ON THURSDAY.
HOWEVER THE LATEST NORTHWEST RIVER FORECAST CENTER MODEL KEEPS IT
BELOW FLOOD STAGE...SO WE FEEL IT DOES NOT WARRANT A FLOOD WATCH AT
THIS TIME.

FLOODING IS NOT EXPECTED ON ANY OTHER RIVER IN THE FORECAST AREA
DURING THE NEXT 7 DAYS.   MCDONNAL

&&

.AVIATION...MODERATE SOUTHWESTERLY FLOW ALOFT WILL CONTINUE TODAY.
AT THE SURFACE STRONG SOUTHEASTERLY GRADIENTS WILL PERSIST TODAY AS
A FRONT MOVES INLAND. THE AIR MASS IS MOIST AND STABLE.

WESTERN WASHINGTON WILL BE BETWEEN SYSTEMS UNTIL 12Z-15Z. A STRONG
WEATHER SYSTEM WILL REACH THE COAST WEDNESDAY MORNING AND MOVE
INLAND DURING THE DAY. PRECIPITATION WILL BEGIN AS SNOW IN SOME
AREAS BUT TURN TO ALL RAIN BY 18Z OR SO. CEILINGS WILL FALL FROM VFR
TO MVFR EVERYWHERE.

KSEA...DISCUSSION ABOVE APPLIES. WINDS WILL BE SOUTHEAST 8-12 KT
EARLY THIS MORNING RISING TO SOUTH 12G22 KT AFTER 18Z. CHB

&&

.MARINE...A STRONG WEATHER SYSTEM WILL MOVE ONSHORE THIS MORNING.
STRONG SOUTHEAST GALES WILL RESULT OVER MOST WATERS TODAY. AFTER A
RELATIVE LULL THIS EVENING...ANOTHER SYSTEM WILL BRING MORE
SOUTHEAST GALES ON THURSDAY. A SURGE OF SOUTHWESTERLY WIND WILL
FOLLOW ON FRIDAY.

THE FORECAST GETS HAZY AFTER THAT AS MODELS DIFFER SIGNIFICANTLY IN
THE TRACK OF THE NEXT LOW. THE NEW GFS AND EURO MODELS MOVE THE LOW
RIGHT OVER WESTERN WASHINGTON...MOVING FROM SOUTHWEST TO NORTHEAST.
THIS IS A WINDY BUT NOT TOO WINDY SCENARIO. THE NEW NAM WANTS TO
KEEP THE LOW IN OREGON. THIS STORM CERTAINLY BEARS WATCHING. CHB

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WINTER STORM WARNING FOR THE CASCADES AND OLYMPICS THROUGH
     THROUGH THURSDAY.
    .WINTER STORM WARNING FOR THE HOOD CANAL AREA THIS MORNING.
    .WIND ADVISORY FOR THE COAST AND NORTH INTERIOR TODAY.
PZ...GALE WARNING ALL WATERS EXCEPT CENTRAL STRAIT AND PUGET SOUND.
     SMALL CRAFT ADVISORY CENTRAL STRAIT AND PUGET SOUND.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.

&&

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