Winter Storm Warning 2, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
930 AM PDT SUN MAR 28 2010

.SYNOPSIS...SHOWERS WILL CONTINUE TODAY WITH SOME SUN BREAKS. A
STRONG COLD FRONT WILL APPROACH THE AREA TONIGHT THEN MOVE INLAND
EARLY MONDAY MORNING...BRINGING RAIN...WINDY CONDITIONS...AND SNOW
TO THE MOUNTAINS. A BROAD UPPER LEVEL TROUGH WILL SETTLE OVER THE
PACIFIC NORTHWEST FOR COOL SHOWERY WEATHER THROUGH MIDWEEK. ANOTHER
FRONT WILL ARRIVE THURSDAY NIGHT OR FRIDAY.

&&

.SHORT TERM...FRONT MOVED THROUGH PUGET SOUND AROUND 10Z IF THE WIND
SWITCHING FROM SOUTHEAST TO SOUTHWEST IS ANY INDICATION. RADAR SHOWS
STEADY PRECIPITATION LIMITED TO THE CASCADES WITH SHOWERY CONDITIONS
ELSEWHERE. VISIBLE SATELLITE PICTURE SHOWS A LARGE CLEAR AREA OFF
THE COAST. FLOW IS PROGRESSIVE SO THERE WILL BE SOME CLEARING OVER
WESTERN WASHINGTON THIS AFTERNOON. WITH SLIGHTLY UNSTABLE CONDITIONS
SKIES WILL NOT GET ANY BETTER THAN MOSTLY CLOUDY...AND A FEW SUN
BREAKS MIGHT BE ALL SOME AREAS GET. HIGHS WILL BE IN THE MID 50S.

A STRONGER STORM IS BARRELING TOWARD THE COAST. RAIN WILL BEGIN
AGAIN THERE LATE THIS AFTERNOON AND INCREASE THIS EVENING. THE
OLYMPICS WILL GET 2-4 INCHES OF MOISTURE IN THE 12 HOUR PERIOD FROM
00Z THIS AFTERNOON TO 12Z MONDAY MORNING. THIS IS LIKELY TO MAKE THE
SKOKOMISH RIVER FLOOD ON MONDAY. MORE ON THIS IN THE HYDROLOGY
SECTION BELOW.

PRESSURE GRADIENTS ARE FORECAST TO BE STRONG WITH THE STORM TONIGHT.
STRONGEST WIND WILL BE ON THE COAST AND A HIGH WIND WARNING IS
LOOKING INCREASINGLY LIKELY THERE...WITH ADVISORY LEVEL WINDS OVER
AT LEAST THE NORTH INTERIOR AND POSSIBLY EVEN THE SEATTLE METRO
AREA. WILL ANALYZE THIS MORE FOR THE AFTERNOON PACKAGE. WINDS CALM A
BIT ON MONDAY AND RAIN WILL CHANGE TO SHOWERS. HIGHS MONDAY WILL BE
LOWER THAN TODAY...PROBABLY AROUND 50.

SNOW LEVELS WILL START THIS EVENING AROUND 4000 FEET BUT WILL FALL
TO 2000 FEET ON MONDAY. HEAVY SNOW IN THE MOUNTAINS IS LIKELY AND
WILL PROBABLY GO TO A WINTER STORM WARNING THIS AFTERNOON FOR THE
MOUNTAINS. THE HEAVIEST SNOW WILL BE TONIGHT THROUGH MONDAY NIGHT
BUT SNOW WILL KEEP FALLING IN THE MOUNTAINS OFF AND ON TUESDAY. IN
FACT NEXT WEEK IS QUITE COOL AND WITH SHOWERS IN THE FORECAST...CAN
NOT RULE OUT SNOW FLURRIES IN THE LOWLANDS ON COLD MORNINGS NEXT
WEEK. BURKE

.LONG TERM...PREVIOUS DISCUSSION...A LARGE UPPER LEVEL TROUGH
FOLLOWING MONDAYS COLD FRONT WILL MAINTAIN SW FLOW ALOFT OVER W WA
TUESDAY AND WEDNESDAY...WITH THE TROUGH AXIS REACHING THE WA COAST
THURSDAY MORNING. THE AIR MASS WILL BE COOL AND GENERALLY UNSTABLE
FOR SCATTERED SHOWERS THROUGH THE PERIOD. LOOKS LIKE THURSDAY WILL
END UP BEING THE DRIEST PERIOD WITH THE TROUGH DEPARTING. GFS/ECMWF
STILL DIFFER ON HOW QUICKLY THE NEXT FRONTAL SYSTEM
ARRIVES...THURSDAY NIGHT FOR THE GFS AND FRIDAY FOR THE ECMWF.
ANOTHER UPPER LEVEL TROUGH AND A SHOWERY PERIOD FOLLOWED THE FRONT
FRIDAY NIGHT THROUGH NEXT WEEKEND. KAM

&&

.HYDROLOGY...MODELS CONSISTENT IN SHOWING 2-4 INCHES OF RAIN OVER
THE OLYMPICS TONIGHT AND MONDAY MORNING...WITH THE BULK FALLING IN A
12 HOUR PERIOD 00Z-12Z. THIS EVENT IS SIMILAR TO AN EVENT ON OCTOBER
31 2009...WHEN HEAVY RAIN OVER 12 HOURS DROVE THE SKOKOMISH RIVER
OVER FLOOD STAGE. THE VOLUME OF WATER FORECAST TO FALL ON THE
SKOKOMISH BASIN IS AS MUCH OR MORE THAN FELL ON OCTOBER 31. SNOW
LEVEL WILL BE AROUND 4000 FEET DURING MOST OF THIS EVENT WHICH MEANS
BASICALLY THE WHOLE SKOKOMISH BASIN WILL HAVE RAIN NOT SNOW.

CURRENT RIVER GUIDANCE REFLECTS THIS THINKING WITH THE RIVER
FORECAST TO REACH FLOOD STAGE ON MONDAY. A FLOOD WATCH IS IN EFFECT
FOR MASON COUNTY. UNLESS THERE IS A RADICAL CHANGE IN THE MODELS
WILL PROBABLY GO TO A WARNING FOR THE SKOKOMISH THIS AFTERNOON. BURKE

WITH THE STRONGEST FLOW OUT OF THE SOUTH...THIS FRONTAL SYSTEM IS
NOT EXPECTED TO PRODUCE A FLOOD THREAT FOR OTHER WESTERN WASHINGTON
RIVERS...INCLUDING THE GREEN RIVER. BURKE

&&

.AVIATION...SHOWERS EXPECTED ACROSS MUCH OF W WA TODAY AS A BROAD
UPPER LEVEL TROUGH SHIFTS INLAND. SLY WINDS WILL ALSO INCREASE
TONIGHT AS ANOTHER STRONG COLD FRONT MOVE IN. HIGHEST WINDS WILL BE
ALONG THE COAST AND NORTH INTERIOR. THIS NEXT SYSTEM WILL PASS
THROUGH THE AREA EARLY MON MORNING AROUND 12Z...WITH STRONG
PERSISTENT ONSHORE FLOW DEVELOPING. 33

KSEA...SHOWERS ACROSS THE PUGET SOUND AREA WILL DECREASE BY THE
AFTERNOON. WINDS WILL REMAIN SLY...INCREASING TONIGHT. RAIN WILL
ALSO INCREASE TONIGHT AS ANOTHER FRONT PASSES SE THROUGH THE REGION.
33

&&

.MARINE...FIRST COLD FRONT PASSED THROUGH W WA EARLY THIS
MORNING...WITH A SECOND ONE APPROACHING TONIGHT. THIS SECOND FRONT
WILL ALSO BE STRONG WITH GALE WARNINGS POSTED FOR MOST WATERS. MAY
NEED TO ADD GALES FOR PUGET SOUND/HOOD CANAL AND THE CENTRAL STRAIT.
COASTAL WATERS WILL BE HIGH END GALE...WITH BRIEF STORM FORCE WINDS
POSSIBLE. WILL RE-EVALUATE LATEST GUIDANCE FOR THE AFTERNOON
PACKAGE. THIS SYSTEM WILL PASS THROUGH MON MORNING...WITH STRONG
ONSHORE FLOW PERSISTING THROUGH TUE. ANOTHER FRONT WILL ARRIVE LATE
IN THE WEEK. 33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WATCH FOR MASON COUNTY.
     HIGH WIND WATCH FOR THE WASHINGTON COAST TONIGHT.
     WINTER STORM WATCH FOR THE OLYMPICS AND CASCADES TONIGHT
     THROUGH MONDAY NIGHT.
PZ...GALE WARNING COASTAL WATERS...ENTRANCES TO THE
     STRAIT...NORTHERN INLAND WATERS AND ADMIRALTY INLET.
     SMALL CRAFT ADVISORY CENTRAL STRAIT AND PUGET SOUND.

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