Small Craft Advisory 48, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
922 AM PST SUN FEB 28 2016

.SYNOPSIS...A COLD FRONT WAS CROSSING WESTERN WASHINGTON THIS
MORNING. IT WILL BE FOLLOWED BY WINDY AND SHOWERY WEATHER THIS
AFTERNOON...WITH LOWERING SNOW LEVELS OVER THE MOUNTAINS. AN
UPPER LEVEL RIDGE WILL BRING A BRIEF DRY PERIOD ON MONDAY. RAIN
WILL RETURN MONDAY NIGHT AND TUESDAY AS A WARM FRONT AND COLD
FRONT CROSS THE AREA. ANOTHER FRONTAL SYSTEM WILL ARRIVE WEDNESDAY
NIGHT WITH ACTIVE WEATHER CONTINUING INTO NEXT WEEKEND.

&&

.SHORT TERM...A WIND SHIFT WITHIN THE PAST HOUR AT HQM AND UIL
INDICATES THAT THE COLD FRONTAL PASSAGE HAS NOW OCCURRED ALONG THE
COAST. COLD FRONT WILL SWEEP INLAND OVER THE NEXT 2 HOURS...THEN
CROSS EAST OF THE CASCADES AROUND NOON. FOLLOWING THE FRONTAL
PASSAGE...THE AIR MASS WILL BECOME QUITE A BIT MORE UNSTABLE...
OWING TO THE ARRIVAL OF COLD AIR ALOFT. IN COMBINATION WITH LOW-
LEVEL ONSHORE FLOW...EXPECTING VIGOROUS CONVECTIVE SHOWER ACTIVITY
THIS AFTN AND EVNG...WITH AN ISOLATED CLAP OR TWO OF LIGHTNING IN
THE FIRST 2-6 HOURS FOLLOWING FROPA. STRONG SE GRADIENTS HAVE
PRECEDED THE FRONT...AND A STRONG SW GRADIENTS WILL FOLLOW THE
FRONT...PEAKING AROUND 4 PM. THIS WILL CAUSE A PICKUP IN S/SW WIND
IN THE METRO AREA ANYTIME NOW...WITH GUSTS NEAR 40 MPH EXPECTED
THIS AFTN. IN THE MTNS...TEMPS WILL BE HOLDING STEADY OR FALLING
THIS AFTN...WITH ABUNDANT SHOWER ACTIVITY AND UPSLOPE FLOW LEADING
TO MODERATE SNOW ACCUMULATIONS. A WINTER WEATHER ADVISORY IS IN
EFFECT FOR THE CASCADES TO COVER THE SNOW FORECAST.

WIND AND SHOWER ACTIVITY WILL SLOWLY TAPER OFF DURING THE COURSE
OF THE OVERNIGHT HOURS AND EARLY MORNING HOURS ON MONDAY. SHOWER
ACTIVITY WILL END LAST OVER THE CASCADES...WITH ACTIVITY ENDING
THERE BY NOON MONDAY. A DRY BREAK BETWEEN WEATHER SYSTEMS IS
EXPECTED FROM MID-DAY MONDAY INTO MON AFTN.

SW FLOW ALOFT WILL QUICKLY INCREASE LATE MON...PUSHING A WARM
FRONT AND STEADY RAIN INTO WRN WA EARLY MON EVNG. STEADY RAIN WILL
MOSTLY CONTINUE UNTIL THE FOLLOWUP OF A COLD FRONTAL PASSAGE
DURING THE DAY TUE. IT WILL BE PRECEDED BY GUSTY E/SE WINDS FOR
THE COAST AND NORTH INTERIOR...THEN FOLLOWED ON TUE AFTN BY GUSTY
W/SW WINDS MOST EVERYWHERE. SNOW LEVELS WILL BE NEAR 6000 FEET IN
THE WARM SECTOR TUE MORNING...THEN FALL TO ABOUT 3500 FEET ON TUE
EVNG BEFORE POST-FRONTAL SHOWER ACTIVITY ENDS.		HANER

.LONG TERM...FROM PREVIOUS DISCUSSION...AFTER TUESDAYS COLD FRONT
THE ASSOCIATED UPPER LEVEL TROUGH SHOULD BE E OF THE AREA BY
TUESDAY EVENING. ANOTHER TRANSITORY UPPER LEVEL RIDGE SHOULD
RESULT IN A DRY WEDNESDAY. THE NEXT FRONTAL SYSTEM SHOULD BEGIN
MOVING OVER THE AREA WEDNESDAY NIGHT. A DEEP BROAD UPPER LEVEL
TROUGH OVER THE NE PACIFIC SHOULD MAINTAIN MOIST SW FLOW ALOFT AND
AN ACTIVE WEATHER PATTERN OVER W WA THROUGH NEXT WEEKEND. KAM

&&

.AVIATION...A FRONT AND UPPER LEVEL TROUGH WILL MOVE THROUGH THE AREA
TODAY. UPPER LEVEL FLOW WILL BE SOUTHWESTERLY TODAY...WESTERLY THIS
EVENING...THEN NORTHWESTERLY LATE TONIGHT. SURFACE FLOW WILL BE
SOUTHEASTERLY AHEAD OF THE FRONT THEN SOUTHWESTERLY BEHIND IT. AIR
MASS IS MOIST AND STABLE EXCEPT SLIGHTLY UNSTABLE THIS AFTERNOON
OFF THE COAST.

CEILINGS THIS MORNING ARE VFR 3-5K FT INLAND BUT MVFR CEILINGS 2-3K
FT ARE SPREADING INLAND FROM THE COAST. RAIN WILL FALL AT TIMES
TODAY...TURNING MORE SHOWERY IN THE AFTERNOON. SUN BREAKS ARE
POSSIBLE LATE THIS AFTERNOON BUT CEILINGS WILL PROBABLY BE MOSTLY
MVFR TONIGHT.

KSEA...DISCUSSION ABOVE APPLIES. VFR BECOMING MVFR LATE THIS MORNING
WITH RAIN. SOUTHERLY WIND 8-12 KT INCREASING TO 15G25 KT BY LATE
MORNING. CHB

&&

.MARINE...A FRONTAL SYSTEM WILL MOVE THROUGH THE REGION TODAY. GALE
WARNINGS ARE IN EFFECT ON THE COAST...AT THE EAST ENTRANCE...AND
OVER THE NORTHERN INLAND WATERS. MOST OF THESE AREAS ARE ALREADY
SHOWING GALE FORCE WINDS. SMALL CRAFT ADVISORIES ARE IN EFFECT FOR
ALL OTHER WATERS. WINDS IN PUGET SOUND AND ADMIRALTY INLET COULD
APPROACH GALE FORCE THIS AFTERNOON. ONSHORE FLOW THIS EVENING WILL
BRING 20-30 KT WESTERLY WINDS TO THE STRAIT...AND THESE ALSO COULD
APPROACH GALE FORCE.

FLOW WILL BE LIGHT OFFSHORE ON MONDAY. ANOTHER SYSTEM COULD BRING
GALES TUESDAY. A WEAKER FRONT MAY ARRIVE THURSDAY. CHB/SMR

&&

.HYDROLOGY...A PERIOD OF MODERATE TO HEAVY RAIN IS FORECAST OVER
THE HEADWATERS OF THE SKOKOMISH RIVER ON MONDAY NIGHT AND
TUESDAY...CONCURRENT WITH SNOW LEVELS IN EXCESS OF 6000 FEET.
BETWEEN 2 AND 3 INCHES OF RAIN ARE FORECAST IN 24 HOURS. THIS MAY
BE ENOUGH TO BRING MINOR FLOODING ON THE SKOKOMISH RIVER STARTING
TUESDAY...BASED ON THE CURRENT FLOOD STAGE OF 16.5 FEET FOR THE
SKOKOMISH RIVER AT POTLATCH.

SEDIMENTATION IN THE WHITE RIVER HAS REDUCED THE RIVER'S ABILITY
TO CARRY MODERATE FLOWS OF WATER WITHOUT CAUSING FLOODING PROBLEMS
NEAR PACIFIC. NO SIGNIFICANT FLOOD IMPACTS HAVE BEEN REPORTED UP
TO THIS POINT...BUT THE RIVER IS NEAR THE LEVEL WHERE LOCALIZED
FLOODING IS POSSIBLE. CONTINUE TO MONITOR THE LATEST FLOOD
STATEMENTS FOR THE MOST UP TO DATE INFORMATION.

ELSEWHERE...NO RIVER FLOODING IS EXPECTED FOR THE NEXT 7 DAYS.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WINTER WEATHER ADVISORY UNTIL 4 AM PST MONDAY FOR CASCADES OF
     PIERCE AND LEWIS COUNTIES-CASCADES OF WHATCOM AND SKAGIT
     COUNTIES.

     WINTER WEATHER ADVISORY FROM NOON TODAY TO 4 AM PST MONDAY FOR
     CASCADES OF SNOHOMISH AND KING COUNTIES.

PZ...GALE WARNING COAST...EAST ENTRANCE...NORTHERN INLAND WATERS.

     SMALL CRAFT ADVISORY ALL OTHER WATERS.

     SMALL CRAFT ADVISORY FOR ROUGH BAR GRAYS HARBOR.

&&

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