Winter Storm Watch 6, NWS Seattle, WA

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE SEATTLE WA
344 PM PST THU FEB 23 2012

UPDATED THE SHORT TERM SECTION.

.SYNOPSIS...A WARM FRONT WILL BRUSH THE FAR WESTERN PART OF THE
STATE FRIDAY MORNING. THIS WILL BE FOLLOWED BY A STRONG COLD FRONT
LATE IN THE DAY FRIDAY. THIS FRONT WILL NOT ONLY BRING GUSTY WINDS
AND LOCALLY HEAVY PRECIPITATION BUT IT WILL ALSO USHER IN A COLDER
AIR MASS. THE SNOW LEVELS WILL PLUMMET TO NEAR 1000 FEET ON
SATURDAY. A CHILLY AND UNSTABLE AIR MASS WILL REMAIN OVER THE AREA
THROUGH SUNDAY FOR A THREAT OF RAIN OR SNOW SHOWERS.

&&

.SHORT TERM...
THE LANGLEY HILL RADAR /KLGX/ SHOWED THE LEADING EDGE OF THE RAIN
SHIELD ASSOCIATED WITH A WMFNT ABOUT 50 MILES OFFSHORE. THERE WERE
SOME LIGHT SHOWERS POPPING OVER THE CWA THIS AFTERNOON WELL AHEAD OF
THE WMFNT. WENT ON AHEAD AND SPED UP THE TIMING OF THE PRECIP OVER
THE CWA...HOWEVER THE NW PORTION WILL HAVE THE HIGHEST THREAT OF
MEASURABLE PRECIP.

THE WMFNT WILL BRUSH THE FAR WRN PART OF THE CWA TOMORROW MORNING
AND THERE WILL PROBABLY BE A BREAK IN THE PRECIP ACROSS MUCH OF THE
INTERIOR BEFORE THE COLD OR OCCLUDED FRONT ARRIVES LATER. THE PRECIP
RATES WILL DEFINITELY INCREASE ON THE SW FACING SLOPES OF THE
OLYMPICS AND N CASCADES DURING THE DAY FRI...THUS A WINTER WEATHER
ADVISORY WAS ISSUED FOR THE OLYMPICS AND A WINTER STORM WARNING FOR
THE N CASCADES. THE PRECIP WILL NOT PICK UP OVER THE CENTRAL
CASCADES UNTIL LATER FRI AFTERNOON...THUS A WINTER STORM WATCH WAS
ISSUED FOR THIS AREA. THE WIND IN THE LOWER TO MID LEVELS OF THE
ATMOSPHERE WILL HAVE A SOUTHERLY COMPONENT TO IT...THUS STEVENS AND
SNOQUALMIE PASSES WILL END UP SOMEWHAT PRECIP SHADOWED UNTIL LATE
FRI NIGHT WHEN THE FLOW BECOMES WLY. SNOWFALL AMOUNTS IN THE
CASCADES WILL BE ON THE ORDER OF 1-2 FT BY LATE IN THE DAY SATURDAY.

THE COLD...UPPER TROF WILL MOVE OVER THE REGION ON SATURDAY AND THE
SNOW LEVELS WILL FALL TO NEAR 1K FT. BOTH THE NAM AND GFS WERE
INDICATING BANDED SHOWERS OVER THE CWA ON SATURDAY...WITH ONE OF
THOSE BANDS MOST LIKELY THE PUGET SOUND CONVERGENCE ZONE /PSCZ/. THE
AIR MASS WILL BE UNSTABLE ENOUGH FOR A SLIGHT RISK OF ISOLATED
TSTMS...MOST LIKELY WITHIN THE ORGANIZED SHOWER BANDS. DUE TO THE
COLDER AIR MASS...ANTICIPATE THE HEAVY SHOWERS TO CONTAIN A LARGE
AMOUNT OF SMALL HAIL OR GRAUPEL ON SATURDAY. IN FACT...DO NOT BE
SURPRISED IF THE SHOWERS FALL AS SNOW AT TIMES OVER THE HIGHER
ELEVATIONS OF THE EAST PUGET SOUND LOWLANDS.

EXPECT THE UPPER LOW TO SETTLE OVER THE REGION ON SUNDAY FOR A
CONTINUED THREAT OF RAIN OR SNOW SHOWERS. THE PRECIP WILL MOST
LIKELY FALL AS SNOW ON THE HIGHER HILLS ON THE LOWLANDS SATURDAY
NIGHT AND SUNDAY. THESE WILL BE OF THE HIT OR MISS VARIETY. IT IS
POSSIBLE THAT A FEW SPOTS COULD RECEIVE AN INCH OR TWO...ESPECIALLY
IF THE SHOWERS ARE ORGANIZED.

IMPROVING CONDITIONS WILL OCCUR SUNDAY NIGHT AS THE UPPER LOW MOVES
INTO OREGON AND DRY...NORTHERLY FLOW ALOFT BECOMES ESTABLISHED OVER
THE CWA.

.LONG TERM...
IT APPEARS THAT MON WILL BE A DRY DAY UNDER RIDGING ALOFT.  BEYOND
MON...THE WEATHER PATTERN WILL BECOME ACTIVE AGAIN FOR UNSETTLED
WEATHER CONDITIONS. THE REGION WILL ALSO REMAIN IN A COOL PATTERN...
THUS THERE WILL BE THE POSSIBILITY OF LOWLAND SNOW WITH THESE
SYSTEMS. IN SHORT...EXPECT BELOW NORMAL TEMPS AND NEAR NORMAL PRECIP
DURING THIS PERIOD.

&&

.HYDROLOGY...
FLOODING CONTINUED ON THE GREEN RIVER AT AUBURN AND THE SNOQUALMIE
RIVER AT CARNATION BUT BOTH HAVE ALREADY CRESTED AND WERE RECEDING.
A FLOOD WATCH WAS ISSUED FOR THE WHITE RIVER IN KING AND PIERCE
COUNTIES DUE TO RELEASES FROM MUD MOUNTAIN DAM. THERE IS A
POSSIBILITY THAT THE RELEASES WILL REACH OR EXCEED THE FLOOD FLOW OF
8000 CFS DURING THE NEXT 24 HOURS.

THE NEXT SYSTEM WILL BRING ANOTHER ROUND OF HEAVY PRECIP ON THE SW
FACING SLOPES OF THE OLYMPICS AND CASCADES ON FRI. THE SNOW LEVELS
WILL BRIEFLY POP UP TO 3500-4K FT ON THE OLYMPICS AND UP TO 4500 FT
ON THE CENTRAL CASCADES FRI. ANOTHER 1-2 INCHES OF RAIN IS EXPECTED
IN THE 24-HOUR PERIOD ENDING AT 4 AM PST SATURDAY ON THE SW FACING
SLOPES. THIS SHOULD BE ENOUGH TO CAUSE SOME RISES ON SOME RIVERS...
WITH SHARP RISES EXPECTED ON THE SKOKOMISH. AT THIS TIME...NEW OR
ADDITIONAL RIVER FLOODING IS NOT EXPECTED.

ANTICIPATE THE SNOW LEVEL TO FALL TO NEAR 1K FT ON SATURDAY AND THIS
WILL END OF THE THREAT OF SIGNIFICANT RAINFALL ON THE RIVERS
FLOWING OUT OF THE MOUNTAINS. A COOL PATTERN WILL PERSIST THRU NEXT
THU...WHICH WILL MEAN THAT FLOODING WILL BE NOT BE EXPECTED SATURDAY
THRU THE END OF NEXT WEEK.

&&

.AVIATION...KATX RADAR IS SHOWERING WEAK ECHOES ACROSS WESTERN WA
THIS AFTERNOON...MAINLY AFFECTING THE CASCADES. CIGS DID POP UP TO
VFR RANGE AND THIS TREND WILL CONTINUE THIS EVENING.

A WARM FRONT WILL BRUSH THE AREA LATE TONIGHT WITH A COLD FRONT
MOVING INLAND ON FRI. EXPECT LOWERING CIGS WITH RAIN AFFECTING THE
COAST AFTER MIDNIGHT. LIGHT PRECIP IS POSSIBLE IN THE INTERIOR FRI
MORNING...BUT HEAVIER PRECIP WILL HOLD OFF UNTIL THE AFTERNOON. MAY
SEE MVFR CONDITIONS. GUSTY SOUTH WINDS WILL ACCOMPANY THIS
SYSTEM...ESPECIALLY ALONG THE COAST AND NORTH PART. 33

KSEA...VFR CONDITIONS THIS EVENING WITH LIGHT SLY WINDS. MAY SEE
LIGHT PRECIP FRI MORNING...BUT EXPECT HIGHER CHANCES IN THE
AFTERNOON AS A COLD FRONT MOVES INLAND. CIGS WILL LOVER TO MVFR WITH
GUSTY S WINDS. 33

&&

.MARINE...A VIGOROUS LOW PRES CENTER WILL SPIN OFF THE WA COAST ON
FRI WITH S/SE GALES FORECAST OVER THE WATERS...PARTICULARLY THE
COASTAL WATERS...EAST ENTRANCE...ADMIRALTY INLET AND NORTHERN INLAND
WATERS. A GALE WARNING IS IN EFFECT FOR THE ZONES MENTIONED AND
SHOULD SEE SOUTH WINDS INCREASING TO 25 TO 35 KT DURING THE EARLY
MORNING HOURS. THIS SYSTEM WILL MOVE INLAND FRI NIGHT INTO SAT BUT
MODELS SHOW STRONG NW FLOW BEHIND. SO EXPECT NW GALES AGAIN OVER THE
COASTAL WATERS AND PROBABLY THROUGH THE STRAIT OF JUAN DE FUCA
THROUGH SAT. SEAS WILL ALSO BUILD TO 20-25 FT. ONSHORE FLOW WILL
WEAKEN BY SUNDAY AFTERNOON. THE NEXT COLD FRONT WILL ARRIVE ON
TUESDAY. 33

&&

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

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

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

     WINTER STORM WATCH FROM FRIDAY AFTERNOON THROUGH SATURDAY
     AFTERNOON FOR THE WEST SLOPES CENTRAL CASCADES ABOVE 3000 FEET.

PZ...GALE WARNINGS ARE IN EFFECT FOR ALL WATERS EXCEPT THE
     CENTRAL STRAIT OF JUAN DE FUCA AND THE PUGET SOUND/HOOD
     CANAL.

     SMALL CRAFT ADVISORY FROM 4 AM TO 6 PM PST FRIDAY FOR THE
     PUGET SOUND AND HOOD CANAL.

     SMALL CRAFT ADVISORY FOR ROUGH BAR IN EFFECT UNTIL 4 PM PST
     FRIDAY FOR THE GRAYS HARBOR BAR.

&&

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