Heavy Snow in Washington, February 24 to 25, 2012

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
415 AM PST FRI FEB 24 2012

.SYNOPSIS...A WARM FRONT WILL BRING RAIN TO THE NORTHWEST PART OF
WESTERN WASHINGTON THIS MORNING. A STRONG COLD FRONT WILL MOVE
THROUGH LATE THIS AFTERNOON AND EARLY THIS EVENING WITH RAIN AND
GUSTY WINDS AND HEAVY SNOW IN THE MOUNTAINS. A COLD SHOWERY AIR MASS
WILL MOVE INLAND SATURDAY WITH THE SNOW LEVEL FALLING TO AROUND 1000
FEET. RAIN OR SNOW SHOWERS ARE POSSIBLE SUNDAY.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS WARM FRONT LIFTING NORTH OF
WESTERN WASHINGTON THIS MORNING WITH THE TRAILING COLD FRONT BACK
OUT NEAR 133W. LOTS OF ECHOES ON THE WSR-88D'S THIS MORNING BUT MOST
OF THE PRECIPITATION IS REMAINING ALOFT WITH JUST A FEW HUNDREDTHS
REPORTED ALONG THE NORTH COAST AND NORTHWEST INTERIOR. SHARP BACK
EDGE TO THE COLD FRONT ON THE SATELLITE IMAGERY A GOOD INDICATION
THAT THE FRONT WILL HAVE SOME PUNCH TO IT. CURRENT TIMING HAS THE
FRONT TO THE COAST NEAR 00Z AND INTO THE CASCADES BY 06Z. THE FRONT
IS FAIRLY NARROW WITH THE PRECIPITATION OUT AHEAD OF THE FRONT
BEGINNING ABOUT 3 TO 6 HOURS AHEAD OF THE FRONTAL PASSAGE. THIS PUTS
THE BEGINNING OF THE COLD FRONT RAIN FOR THE INTERIOR INTO THE
AFTERNOON HOURS. WINDY CONDITIONS OVER THE NORTHERN PORTION OF THE
AREA AHEAD OF THE FRONT WITH STRONG ONSHORE FLOW BEHIND THE FRONT
RESULTING IN WINDY CONDITIONS FOR THE ENTIRE AREA ON SATURDAY. AT
THIS POINT IT LOOKS LIKE WINDS WILL STAY BELOW WARNING
CRITERIA...SUSTAINED 40 MPH OR GUSTS TO 60 MPH...BUT NOT BY MUCH
WITH WIND ADVISORIES LIKELY FOR PORTIONS OF THE AREA ON SATURDAY.

SNOW LEVELS AHEAD OF THE FRONT WILL BRIEFLY RISE TO NEAR 4000 FEET
OVER THE CENTRAL CASCADES THEN PLUMMET QUICKLY BEHIND THE FRONT
FRIDAY EVENING TO BELOW ALL PASS LEVELS. STRONG OROGRAPHICS JUST
AHEAD AND WITH THE FRONT WILL RESULT IN PERIODS OF HEAVY SNOW FOR
THE MOUNTAINS. LATER TODAY INTO TONIGHT. WHILE THE OROGRAPHIC FLOW
WEAKENS A TOUCH BEHIND THE FRONT 850-700 MB WINDS STILL IN THE 25 TO
40 KNOT RANGE INTO SATURDAY AFTERNOON. THIS WILL KEEP THE SNOW
PILING UP AND WITH THE COLD AIR MASS COULD SEE AN INCH ACCUMULATION
FROM ONLY .05 INCHES OF WATER. WILL UPGRADE THE WINTER STORM WATCH
TO A WARNING FOR THE CENTRAL CASCADES AND KEEP THE WARNING GOING FOR
THE NORTH CASCADES INTO SATURDAY AFTERNOON.

COLD AIR MASS MOVING INTO WESTERN WASHINGTON BEHIND THE FRONT WITH
THE SNOW LEVELS LOWERING DOWN TO AROUND 1000 FEET ON SATURDAY.
SATELLITE IMAGERY SHOWS PLENTY OF SHOWER ACTIVITY BEHIND THE FRONT.
ALTHOUGH THE AIR MASS WILL BECOME UNSTABLE POST FRONTAL LIFTED
INDEXES REMAIN ABOVE 0 AND THERE IS LITTLE WIND SHEAR ALOFT SO WILL
KEEP THE MENTION OF THUNDERSTORMS OUT OF THE FORECAST. THIS DOES NOT
RULE OUT THAT THE PRECIPITATION IN SOME OF THE SHOWERS WILL BE HEAVY
WHICH COULD TEMPORALLY LOWER THE SNOW LEVEL DOWN TO NEAR THE SURFACE
ON SATURDAY. BY LATE SATURDAY EXPECT ANYWHERE FROM 18 TO 30 INCHES
OF NEW SNOW IN THE NORTH CASCADES AND 12 TO 24 INCHES IN THE CENTRAL
CASCADES.

A SHORTWAVE EMBEDDED IN THE NORTHWESTERLY FLOW ALOFT MOVING DOWN
OVER WESTERN WASHINGTON SUNDAY MORNING INTO THE EARLY AFTERNOON.
THIS WILL BE THE BEST CHANCE FOR ANY ACCUMULATING SNOW IN THE
LOWLANDS WITH SNOW LEVELS DOWN TO NEAR 500 FEET. EVEN IF THERE IS
ACCUMULATING SNOW IT WILL BE LOCALIZED AND NOW WIDESPREAD. HIGH
TEMPERATURES ON SUNDAY WILL BE AROUND 40 DEGREES SO DO NOT EXPECT
THE SNOW TO STICK AROUND EVEN IF WE GET SOME.

.LONG TERM...EXTENDED MODELS ONCE AGAIN IN GOOD AGREEMENT WITH AN
UPPER LEVEL RIDGE BUILDING INTO CENTRAL BRITISH COLUMBIA SUNDAY
NIGHT AND MOVING DOWN OVER WESTERN WASHINGTON ON MONDAY RESULTING IN
A DRY DAY FOR THE REGION. RIDGE SLIDES EAST MONDAY NIGHT OPENING THE
DOOR FOR THE NEXT FRONT TO MOVE INTO WESTERN WASHINGTON DURING THE
LATTER HALF OF TUESDAY. SIMILAR SCENARIO WITH THIS FRONT AS WITH THE
ONE FOR TONIGHT WITH A COLD UPPER LEVEL TROUGH SETTLING OVER THE
AREA BEHIND THE FRONT WEDNESDAY RESULTING IN ANOTHER ROUND OF LOW
SNOW LEVELS AND SIGNIFICANT SNOWS FOR THE MOUNTAINS. POSSIBLE BREAK
IN THE ACTION THURSDAY WITH AN UPPER LEVEL RIDGE BUILDING OFFSHORE
BUT FOR NOW WILL STAY WITH THE CHANCE POPS FOR DAY 7. FELTON

&&

.HYDROLOGY...MINOR FLOODING WILL COME TO AN END THIS MORNING ALONG A
REACH OF THE GREEN RIVER. THE FLOOD WATCH WILL REMAIN IN EFFECT FOR
THE WHITE RIVER. IT IS RUNNING CLOSE TO FLOOD STAGE AS WATER IS
RELEASED FROM MUD MOUNTAIN DAM...AND MINOR FLOODING THERE IS STILL A
POSSIBILITY.

THE NEXT FRONTAL SYSTEM WILL ARRIVE LATE THIS AFTERNOON INTO THIS
EVENING. IT DOES NOT POSE A THREAT OF FLOODING FOR THE
RIVERS...WITH THE POSSIBLE EXCEPTION OF THE SKOKOMISH RIVER AND EVEN
THAT POSSIBILITY LOOKS SLIGHT. IT WILL BRING STORM TOTAL
PRECIPITATION AMOUNTS OF 1 TO 2.5 INCHES TO THE MOUNTAINS. THE SNOW
LEVEL WILL BE FAIRLY LOW...EXCEPT FOR A BRIEF RISE TO AROUND 4000 FT
THIS AFTERNOON AHEAD OF THE FRONT. A COOL WEATHER PATTERN WILL
PREVAIL THIS WEEKEND AND EARLY NEXT WEEK...AND THERE WILL NOT BE ANY
FLOODING. FELTON

&&

.AVIATION...A WARM FRONT IS BRUSHING WESTERN WA THIS MORNING AND THE
COLD FRONT WILL REACH THE COAST THIS AFTERNOON AND MOVE INTO THE
CASCADES THIS EVENING. GUSTY SOUTH WINDS WILL ACCOMPANY THIS
SYSTEM...ESPECIALLY ALONG THE COAST AND IN THE NORTH
INTERIOR...ESPECIALLY THE TYPICAL AREAS FROM ADMIRALTY INLET AND
WHIDBEY ISLAND UP THRU THE SAN JUANS. MTNS OBSCD. 19

KSEA...RAIN AT TIMES THIS AFTERNOON AND EVENING AND BREEZY BY THIS
EVENING. WINDY SATURDAY MORNING...PDX-BLI GRADIENT ON THE NAM AT 12Z
SAT IS FCST TO BE ARND +13MB.

&&

.MARINE...SLY GALES FORECAST FOR THE COASTAL WATERS...EAST
ENTRANCE...ADMIRALTY INLET AND NORTHERN INLAND WATERS. THE SYSTEM
WILL MOVE INLAND TONIGHT INTO SAT AND THE MODELS HAVE BEEN
CONSISTENTLY SHOWING STRONG SW FLOW INTO PUGET SOUND BY DAYBREAK
SATURDAY AND STRONG NW FLOW OVER THE COASTAL WATERS...AND A FULL WLY
GALE IN THE STRAIT OF JUAN DE FUCA SAT. SEAS WILL BUILD TO ARND 22FT
SAT OVER THE COASTAL WATERS. ONSHORE FLOW WILL WEAKEN BY SUNDAY
AFTERNOON. THE NEXT COLD FRONT WILL ARRIVE ON TUESDAY. 19

&&

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WARNINGS/WATCHES REMAIN IN EFFECT FOR PARTS OF THE CWA.

     WINTER STORM WARNING FROM 6 AM TODAY TO 6 PM PST SATURDAY
     FOR THE WEST SLOPES NORTHERN CASCADES ABOVE 2000 FEET.

     WINTER WEATHER ADVISORY FROM 6 AM TODAY TO 4 AM PST SATURDAY
     FOR THE OLYMPICS ABOVE 2500 FEET.

     WINTER STORM WARNING FROM 3 PM TODAY TO 6 PM SATURDAY FOR THE
     WEST SLOPES CENTRAL CASCADES ABOVE 3000 FEET.

PZ...GALE WARNING COASTAL WATERS...ENTRANCES TO THE STRAIT
     ...ADMIRALTY INLET...NORTHERN INLAND WATERS.
     SMALL CRAFT ADVISORY PUGET SOUND AND HOOD CANAL.
     SMALL CRAFT ADVISORY GRAYS HARBOR BAR.

&&

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