Heavy Snow in Washington, February 12 to 13, 2011

AREA FORECAST DISCUSSION...CORRECTED TYPO AVIATION SECTION
NATIONAL WEATHER SERVICE SEATTLE WA
300 AM PST SAT FEB 12 2011

.SYNOPSIS...A COLD FRONT WILL SPREAD RAIN ACROSS WESTERN WASHINGTON
TODAY AND TONIGHT...WITH WINDY CONDITIONS ESPECIALLY ALONG THE COAST
AND IN THE NORTHWEST INTERIOR. THERE WILL BE A LULL BETWEEN WEATHER
SYSTEMS SUNDAY...WITH WET AND WINDY WEATHER RETURNING SUNDAY NIGHT
THROUGH MONDAY NIGHT AS ANOTHER FRONT MOVES THROUGH. AN UPPER TROUGH
WILL KEEP THINGS COOL AND SHOWERY TUESDAY THROUGH FRIDAY.

&&

.SHORT TERM...A FLAT UPPER RIDGE IS JUST EAST OF THE CASCADES EARLY
THIS MORNING...AND A FAIRLY VIGOROUS PACIFIC FRONTAL SYSTEM IS
POISED JUST OFF THE COAST OF THE PACIFIC NORTHWEST. IN FACT THE WARM
FRONT OF THIS SYSTEM BRUSHED THE NORTHWEST CORNER OF WESTERN
WASHINGTON FRIDAY AFTERNOON AND EVENING AS IT HEADED INTO BRITISH
COLUMBIA. IT PRODUCED JUST SPOTTY LIGHT RAIN IN THAT AREA...BUT
SURPRISINGLY 9 INCHES OF SNOW AT MOUNT BAKER. AT 2 AM WARM FRONTAL
CLOUDS REMAINED OVER THE NORTH PART OF THE AREA WITH TEMPERATURES IN
THE MID 40S TO LOWER 50S...WHILE SKIES HAD CLEARED SOMEWHAT TO THE
SOUTH WITH TEMPERATURES IN THE MID 30S TO MID 40S.

THE COLD FRONT WILL BRING A MORE SIGNIFICANT ROUND OF PRECIPITATION
TO WESTERN WASHINGTON THROUGH THIS EVENING. RAIN WILL DEVELOP ALONG
THE COAST AND IN THE NORTH THIS MORNING AND GENERALLY SPREAD
SOUTHEAST DURING THE DAY. AS THE FRONT MOVES THROUGH TONIGHT THE
STEADY PRECIPITATION WILL TURN TO SHOWERS. THE FRONT WILL ALSO
PRODUCE WINDY CONDITIONS ALONG THE COAST AND IN THE NORTHWEST
INTERIOR. IT SHOULD REMAIN COMFORTABLY BELOW HIGH WIND CRITERIA BUT
I THINK A LOW-END WIND ADVISORY FOR THE NORTHWEST INTERIOR IS
WARRANTED. WE WILL HAVE BREEZY CONDITIONS ELSEWHERE IN THE LOWLANDS.

THE MOST SIGNIFICANT PRECIPITATION AMOUNTS WILL BE IN THE
MOUNTAINS...WHERE FAIRLY HEAVY PRECIPITATION WILL CONTINUE IN STRONG
WESTERLY FLOW TONIGHT BEHIND THE COLD FRONT. THE SNOW LEVEL WILL
INITIALLY BE 4000 TO 5000 FEET TODAY BUT FALL TO AROUND 3000 FEET
TONIGHT. THE HEAVIEST PRECIPITATION WILL PROBABLY FALL AROUND MT
BAKER...AND THAT IS ALSO WHERE THE SNOW LEVEL WILL BE LOWEST. SO
SNOWFALL ACCUMULATION THERE COULD EXCEED 18 INCHES THROUGH TONIGHT.
PRECIPITATION WILL DEVELOP LATER AT MT RAINIER BUT PARADISE HAS A
GOOD CHANCE OF PICKING UP 12 INCHES OF SNOW TONIGHT. THE WINTER
STORM WATCH WILL BE UPGRADED TO WARNING FOR THE CASCADES...BUT NOTE
THAT STEVENS PASS AND ESPECIALLY SNOQUALMIE PASS WILL RECEIVE LESS
SNOW THAN THE VOLCANOES. I WILL GO WITH AN ADVISORY FOR THE
OLYMPICS.

THERE WILL BE A LULL IN THE ACTION SUNDAY...WITH JUST A FEW SHOWERS
IN THE SOMEWHAT COOL AIR MASS BEHIND THE COLD FRONT. ANOTHER WARM
FRONT WILL SPREAD A NEW ROUND OF RAINFALL ACROSS WESTERN WASHINGTON
SUNDAY NIGHT AS IT LIFTS NORTHWARD FROM OREGON. RAIN WILL CONTINUE
AT TIMES MONDAY AND MONDAY NIGHT AS THE WARM FRONT REMAINS OVER THE
AREA AND THEN AS A COLD FRONT MOVES THROUGH FROM THE WEST. THE SNOW
LEVEL WILL RISE TO AROUND 4000 FEET IN THE WARM SECTOR MONDAY...THEN
FALL TO 3000 FEET AGAIN BEHIND THE COLD FRONT MONDAY NIGHT.

THE WINDS WITH THE SYSTEM ON MONDAY ARE AN UNCERTAINTY. WE CAN BE
CONFIDENT THAT IT WILL BE ANOTHER WINDY DAY FOR THE COAST AND THE
NORTHWEST INTERIOR. HOWEVER SOME MODEL SOLUTIONS...ESPECIALLY
PREVIOUS RUNS...INDICATED THE POTENTIAL FOR AT LEAST LOCALIZED HIGH
WINDS. THE LATEST MODEL RUNS ARE IN FAIRLY GOOD AGREEMENT THAT THE
SURFACE LOW WILL TRAVEL ALMOST DUE NORTH ALONG 130W...MOVING ACROSS
QUEEN CHARLOTTE SOUND INTO BRITISH COLUMBIA. THIS SCENARIO WOULD
PROBABLY PRESENT ONLY A POSSIBILITY OF LOW-END WARNING SPEEDS AT THE
COAST.  MCDONNAL

.LONG TERM...LONGER RANGE MODELS ARE IN ROUGH AGREEMENT THAT AN
UPPER TROUGH WILL MOVE OVER THE REGION TUESDAY BEHIND THE FRONTAL
SYSTEM DISCUSSED ABOVE. IT WILL TAKE A FEW DAYS TO MOVE SLOWLY
EASTWARD...WITH NORTHERLY FLOW DEVELOPING AROUND FRIDAY AHEAD OF A
LARGE UPPER RIDGE OFFSHORE. SO TUESDAY THROUGH FRIDAY SHOULD BE A
RATHER COOL PERIOD WITH GENERALLY LIGHT SCATTERED SHOWERS. MOST
LIKELY THERE WILL BE NO ORGANIZED FRONTS MOVING THROUGH.  MCDONNAL

&&

.HYDROLOGY...THE PERIOD OF WETTER WEATHER BEGINNING TODAY AND
CONTINUING THROUGH MONDAY NIGHT COULD EVENTUALLY RESULT IN SOME
FLOODING ON THE SKOKOMISH RIVER...WITH THE BASIN MEAN PRECIPITATION
PROBABLY IN THE 4 TO 5 INCH RANGE. FOR ALL OTHER RIVER BASINS IN
WESTERN WASHINGTON THE PRECIPITATION TOTALS WILL BE MARGINAL...WITH
BREAKS IN PRECIPITATION AND PERIODS OF LOWER SNOW LEVELS PROBABLY
PRECLUDING ANY FLOODING. BEYOND THAT THERE IS NO APPARENT THREAT OF
FLOODING THROUGH THE NEXT TEN DAYS.

FLOODING IS NOT EXPECTED ON THE GREEN RIVER THROUGH THE TEN DAY
PERIOD.  MCDONNAL

&&

.AVIATION...A BROAD FLAT UPPER LEVEL RIDGE OVER CA AND OREGON IS
PRODUCING STRONG W-SW FLOW ALOFT ACROSS W WA. MOISTURE AND S-SE LOW
LEVEL WINDS WILL INCREASE BY LATE MORNING AS A COLD FRONT APPROACHES
FROM THE NW...CROSSING THE N COAST LATE THIS AFTERNOON AND PUGET
SOUND THIS EVENING. EXPECT CIGS TO BEGIN LOWERING AHEAD OF THE COLD
FRONT BY MIDDAY...THEN DROP TO MVFR LATE THIS AFTERNOON AND EVENING.
VISIBILITY SHOULD BE DOWN TO 5SM AT TIMES IN RAIN.

KSEA...EXPECT GOOD VFR CONDITIONS TO CONTINUE THROUGH THIS MORNING
WITH CIGS ABOVE BKN050...THEN DROP TO BKN030-050 IN -RA THIS
AFTERNOON. COULD SEE CIGS DOWN TO BKN020-030 LATE THIS AFTERNOON
JUST AHEAD OF THE COLD FRONT. S SURFACE WINDS 5-10 KT WILL CONTINUE
THROUGH THIS MORNING THEN INCREASE TO 15 TO 25 KT AROUND 21Z. SW
WINDS ALOFT FL050-FL100 WILL BE 40-60KT FROM 15Z THROUGH FROPA THIS
EVENING AROUND 04Z. KAM

&&

.MARINE...A COLD FRONT EXTENDING FROM N VANCOUVER ISLAND SW OVER THE
OFFSHORE WATERS WILL MOVE SE...REACHING THE N COAST LATE THIS
AFTERNOON THEN SWEEPING ACROSS PUGET SOUND THIS EVENING. PER 00Z 4KM
WRF-GFS EXPECT S-SE FLOW INCREASE TO GALES IN MOST ZONES BY LATE
THIS MORNING...ALTHOUGH GALE WINDS WILL NOT BE CONTINUOUS THROUGHOUT
THE PERIOD. STILL EXPECT A WESTERLY PUSH BEHIND THE FRONT THROUGH
THE STRAIT THIS EVENING...SO A SCA IS IN EFFECT FOR THAT. HAVE
GENERALLY FOLLOWED THE GFS FOR SUNDAY THROUGH WEDNESDAY...ALTHOUGH
THERE IS A LACK OF CONFIDENCE IN THE DETAILS ESPECIALLY AFTER
MONDAY. GFS SHOWS A PAIR OF SURFACE LOWS MOVING NORTHWARD OFFSHORE
EARLY NEXT WEEK. THE STRONGER ONE BRINGS ANOTHER ROUND OF GALES TO
THE COAST AND NORTHERN WATERS ON MONDAY WITH A WEAKER LOOKING LOW
LATER ON TUESDAY. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WIND ADVISORY FOR THE NORTHWEST INTERIOR FROM 9 AM THIS MORNING
       TO 9 PM PST THIS EVENING.

     WINTER STORM WARNING FOR THE CASCADES FROM 9 AM THIS MORNING TO
       6 AM PST SUNDAY.

     WINTER WEATHER ADVISORY FOR THE OLYMPICS FROM 6 AM THIS MORNING
       TO 6 AM PST SUNDAY.

PZ...SMALL CRAFT ADVISORY IN EFFECT FOR ALL WATERS EXCEPT THE PUGET
     SOUND/HOOD CANAL THRU TONIGHT.

     GALE WARNING IN EFFECT FOR ALL WATERS EXCEPT THE CENTRAL
     STRAIT OF JUAN DE FUCA SATURDAY MORNING THRU SATURDAY EVENING.

     SMALL CRAFT ADVISORY GRAYS HARBOR FOR ROUGH BAR CONDITIONS.
     SMALL CRAFT ADVISORY SATURDAY EVENING CENTRAL AND EAST STRAIT.

FOR AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION...PLEASE SEE
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML.