Heavy Snow and High Wind in Washington, March 11, 2010

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
855 PM PST WED MAR 10 2010

.SYNOPSIS...A STRONG COLD FRONT WILL BRING RAIN AND LOCALLY WINDY
CONDITIONS TO WESTERN WASHINGTON TONIGHT AS IT MOVES INLAND. PERIODS
OF RAIN WILL CONTINUE THURSDAY AND THURSDAY NIGHT AS THE FRONT
STALLS OVER THE AREA. RAIN AND WIND WILL INCREASE FRIDAY MORNING AS
A SURFACE LOW TRAVELING UP THE STALLED FRONT MOVES NORTHWARD ACROSS
THE WASHINGTON COAST. THE RAIN WILL CHANGE TO SHOWERS FRIDAY
AFTERNOON AS AN APPROACHING UPPER LEVEL TROUGH PUSHES THE FRONT EAST
OF THE AREA. SHOWERS WILL DECREASE SATURDAY AND END SUNDAY AS AN
UPPER LEVEL RIDGE MOVES OVERHEAD. ANOTHER FRONTAL SYSTEM WILL STALL
JUST OFFSHORE SUNDAY INTO EARLY NEXT WEEK.

&&

.SHORT TERM...THE APPROACHING COLD FRONT HAS JUST MOVED EAST OF
50N/130W AT 02Z AND APPEARS TO BE ON TRACK TO REACH THE N COAST
AROUND 12Z. THE MAIN SURFACE WELL OFFSHORE NEAR 53N/138W IS HEADING
TOWARD THE AK PANHANDLE...BUT VERY STRONG PRESSURE GRADIENTS ALONG
THE COLD FRONT WILL GENERATE VERY WINDY CONDITIONS ALONG THE COAST
AND OVER THE N INTERIOR TONIGHT. LATEST 7 PM OBS SHOW THE BLI-YZT
GRADIENT UP TO 17.1 MB AND WINDS STARTING TO COME UP ALONG THE COAST
AND OVER THE N INTERIOR. EXPECT HIGHEST SUSTAINED WINDS IN THE 30S
WITH GUSTS TO 45-55 MPH. WIND ADVISORY FOR THE N INTERIOR LOOKS GOOD
AT THIS POINT WITH THE HIGHEST WINDS BETWEEN 06Z-15Z.

THE MAIN SHORT TERM PROBLEM IS SNOW AMOUNT OVER THE MOUNTAINS. THE
FREEZING LEVEL AT UIL WAS 2600 FEET THIS EVENING AND FREEZING LEVELS
ARE SIMILARLY LOW OVER THE CASCADES. MODELS SHOW SNOW LEVELS
REMAINING AT OR BELOW PASS LEVELS THROUGH THURSDAY MORNING THEN
RISING SLOWLY TO 5000 FEET OR BY EARLY FRIDAY MORNING. THE INBOUND
FRONT WILL GENERATE SOME DECENT SNOW FALL OVER NIGHT...BUT LIGHTER
SNOW SHOULD CONTINUE THIS AFTERNOON AND TONIGHT AS THE FRONT HANGS
UP OVER THE AREA. BOTH 00Z NAM AND 12Z 4 KM WRF-GFS SHOW ENOUGH
QPF/SNOW ACCUMULATION OVER 12 AND 24 HOUR PERIODS THE NEXT COUPLE OF
DAYS TO JUSTIFY A WINTER STORM WARNING. WILL COVER THE PERIOD
THROUGH THURSDAY NIGHT...FIGURING THAT SNOW LEVELS WILL BE ABOVE THE
MAIN CASCADE PASSES ON FRIDAY. SNOW LEVELS WILL BE LOW ENOUGH WITH
THIS FIRST FRONT SO THAT RIVER FLOODING WILL NOT BE A PROBLEM.

AS MENTIONED ABOVE...AFTER THE COLD FRONT MOVES INLAND AFTER 12Z
THURSDAY...IT WILL END UP STALLING OVER W WA DURING THE DAY. STRONG
SW FLOW ALOFT WILL DIMINISH SO THE HEAVY PRECIP OVER THE MOUNTAINS
WILL EASE...BUT PERIODS OF RAIN/SNOW WILL CONTINUE.

NEW 00Z GFS/NAM ARE IN RATHER GOOD AGREEMENT SHOWING AN UPPER LEVEL
TROUGH APPROACHING FROM THE W THURSDAY NIGHT. THIS FEATURE CAUSES A
WAVE TO FORM ON THE FRONT...DEVELOPING INTO A SURFACE LOW THAT MOVES
N JUST W OF THE COASTAL WATERS EARLY FRIDAY MORNING. THIS MAY
PRODUCE ANOTHER VERY WINDY PERIOD MAINLY FOR THE COAST...AND ANOTHER
INCREASE IN RAIN FOR THE REST OF THE AREA. WILL HAVE TO WATCH THE
SKOKOMISH RIVER WITH THIS WAVE...SINCE THE SNOW LEVELS WILL BE
AROUND 5000 FEET.

THE APPROACHING UPPER LEVEL TROUGH DOES MANAGE TO PUSH THE STALLED
FRONT EAST OF THE CASCADES BY FRIDAY AFTERNOON...WITH A SHOWERY
REGIME SETTING UP FOR FRIDAY NIGHT/SATURDAY MORNING. KAM

.LONG TERM...PREVIOUS DISCUSSION FROM THE 4 PM AFD...MODELS TEND TO
BE AGREEING ON BUILDING A RIDGE OVER THE IDAHO/MT BORDER SUNDAY INTO
MONDAY. THIS WILL STAND UP THE NEXT FRONTAL SYSTEM JUST OFFSHORE.
LEFT RAIN IN THE FORECAST FOR THE COAST AND NORTHERN INTERIOR...BUT
REMOVED POPS FROM THE INTERIOR WITH A NOD TO THE DRYING TREND.
DEPENDING ON THE AMOUNT OF SUNSHINE MONDAY COULD END UP BEING QUITE
WARM WITH SURFACE OFFSHORE FLOW DEVELOPING. THE TROUGH WILL PASS
OVER THE AREA ON TUESDAY WITH SHOWERS LINGERING INTO WEDNESDAY.
DAMICO

&&

.HYDROLOGY...RAIN/SNOW DEVELOPS TONIGHT AS A COLD FRONT APPROACHES
THE AREA. SNOW LEVELS ARE LOW...FREEZING LEVEL 2600 FEET AT UIL THIS
EVENING...AND WILL REMAIN BELOW PASS LEVELS THROUGH FRIDAY. THIS
INITIAL FRONT HAS STRONG SW FLOW NEAR 50 KT AT 850 MB THAT WILL
GENERATE HEAVY PRECIP OVER THE OLYMPICS AND N CASCADES...BUT WITH
THE SNOW LEVEL SO LOW...LOWER RUNOFF WILL KEEP RIVERS BELOW FLOOD
STAGE. THE FRONT WILL STALL OVER THE AREA THURSDAY...BUT SNOW LEVELS
WILL REMAIN ON THE LOW SIDE AND PRECIP WILL BE LIGHTER.

A WAVE MOVES UP THE STALLED FRONT EARLY FRIDAY MORNING...FOR ANOTHER
ROUND OF STRONG S-SW FLOW...MAINLY AFFECTING THE OLYMPICS. SNOW
LEVELS LOOK TO BE 4000-4500 FEET WITH PERHAPS ANOTHER 1.5 INCHES OF
RAIN. WILL HAVE TO KEEP AN EYE ON PRECIP TOTALS AND SNOW LEVELS WITH
THIS SECOND WAVE...BUT AT THIS POINT THE RIVER MODELS ARE KEEPING
EVERYTHING BELOW FLOOD STAGE.

AN UPPER LEVEL TROUGH KEEPS SHOWERS GOING THROUGH SATURDAY AND AN
UPPER LEVEL RIDGE SHOULD DRY THE AREA OUT SUNDAY AND MONDAY...AND
POSSIBLY STALLING THE NEXT FRONT OFFSHORE THROUGH TUESDAY. SO...NO
THREAT OF FLOODING IS EXPECTED SATURDAY THROUGH EARLY NEXT WEEK.
THE FLOOD RISK IS LOW THROUGH THE NEXT 10 DAYS FOR THE GREEN RIVER.
KAM

&&

.AVIATION...A STRONG FRONT WILL REACH THE COAST AROUND 09Z...THEN
STALL OVER INTERIOR WRN WA THROUGH THU MORNING. STRONG SLY WINDS
ALOFT WILL BECOME SWLY ON THU. MOISTURE WILL INCREASE AT ALL LEVELS
ACROSS WRN WA THIS EVENING WITH RAIN DEVELOPING AND CONTINUING INTO
FRI MORNING. MVFR CIGS WILL BECOME WIDESPREAD BY MIDNIGHT WITH AREAS
OF IFR.

KSEA...RAIN WILL INCREASE AT THE TERMINAL BY 06Z. CIGS WILL LOWER TO
PREDOMINATELY MFR CONDITIONS AFTER MIDNIGHT. S WIND 8-12
KT...BECOMING AFTER 11Z SW 12-18 KT WITH GUSTS TO 30 KT. DTM

&&

.MARINE...A COUPLE OF STRONG FRONT WILL BRING STRONG WINDS TO ALL
THE COASTAL WATERS AT TIMES THROUGH THE END OF THE WEEK. THE FIRST
FRONT ALREADY ENTERING THE COASTAL WATERS WILL PRODUCE GALE FORCE
WINDS THERE TONIGHT AS WELL AS SOME OF THE INLAND WATERS THROUGH THU
AS THE FRONT WILL BE SLOW TO PUSH THROUGH. STRONG SMALL CRAFT WINDS
ARE EXPECTED IN PLACES LIKE PUGET SOUND NOT UNDER A GALE WARNING. DTM

THE SECOND SYSTEM WILL BE A DEEPENING LOW CENTER THAT WILL LIFT
NORTH OFF THE COAST JUST INSIDE 130W ON FRI. THIS SHOULD BRING
ANOTHER ROUND OF GALES FOR AT LEAST THE COAST AND WEST ENTRANCE. THE
12Z GFS WOULD SUGGEST THE POSSIBILITY OF STORM-FORCE WINDS FOR THE
OUTER COASTAL WATERS ON FRI MORNING...BUT IT SEEMS TO BE AN OUTLIER
FOR NOW. HANER/DTM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WIND ADVISORY NORTH INTERIOR AND ADMIRALTY INLET TONIGHT. SNOW
     ADVISORY MOUNTAINS TONIGHT THROUGH THURSDAY EVENING.
PZ...GALE WARNING COASTAL WATERS...ENTRANCES TO THE STRAIT...
        NORTHERN INLAND WATERS AND ADMIRALTY INLET.
     SMALL CRAFT ADVISORY CENTRAL STRAIT AND PUGET SOUND/HOOD CANAL.
     SMALL CRAFT ADVISORY FOR ROUGH BAR GRAYS HARBOR BAR.

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