Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 211312
AFDSEW

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE SEATTLE WA
512 AM PST FRI NOV 21 2014

CORRECTED THE LONG TERM SEGMENT.

.SYNOPSIS...A STRONG PACIFIC STORM WILL BRING GUSTY WINDS TO THE
AREA AND SNOW TO THE MOUNTAINS THROUGH TONIGHT. EXPECT THE
OCCLUDED FRONT TO SWEEP ACROSS THE REGION LATE TODAY THROUGH THIS
EVENING. UNSETTLED CONDITIONS WILL PREVAIL ON SATURDAY. ALAS...
ANOTHER LOW PRESSURE SYSTEM WILL IMPACT THE AREA ON SUNDAY FOR
MORE SNOW IN THE MOUNTAINS AND LOCALLY GUSTY WINDS.

&&

.SHORT TERM...
PRECIP WAS STARTING TO INCREASE ACROSS THE CWA AHEAD OF THE MAIN
PRECIP SHIELD THAT WAS STILL OFFSHORE AT THIS TIME. SATELLITE
DERIVED PRECIPITABLE WATER /PWAT/ IMAGERY SHOWED THAT THE VIGOROUS
PACIFIC STORM APPROACHING THE PACIFIC NORTHWEST HAS A DECENT
MOISTURE FEED OR PLUME ASSOCIATED WITH IT. THE SATELLITE DERIVED
PERCENT OF NORMAL TOTAL PRECIPITABLE WATER PRODUCT SHOWED THAT
THERE WERE AMOUNTS OVER 200 PERCENT OF NORMAL ASSOCIATED WITH THE
UPCOMING SYSTEM.

THE HEAVIEST PRECIP IS EXPECTED TO FALL ON THE COAST AND IN THE
MOUNTAINS...WHERE TOTAL LIQUID PRECIP AMOUNTS ARE EXPECTED TO BE
IN THE 1 TO 2.5 INCH RANGE DURING THE 24 HOUR PERIOD ENDING AT 4
AM PST SATURDAY. THE CASCADES ABOVE THE 3500 FOOT LEVEL IS
EXPECTED TO RECEIVE 10 TO 16 INCHES OF NEW SNOW BY SATURDAY
MORNING.

STRONG WESTERLY WINDS WILL ALSO HELP TO ENHANCE SNOWFALL AMOUNTS
IN THE CASCADES...SO THERE WILL LIKELY BE LOCALIZED HIGHER
AMOUNTS. ALSO...A PUGET SOUND CONVERGENCE ZONE /PSCZ/ IS EXPECTED
TO DEVELOP LATE TONIGHT OR EARLY SATURDAY AND THIS WILL RESULT
IN LOCALLY HEAVY SNOW IN THE CASCADES NEAR THE KING/SNOHOMISH
COUNTY LINE. THE SNOW LEVELS WILL BRIEFLY RISE LATER TODAY OR
EARLY THIS EVENING BEFORE PLUMMETING TO NEAR 3000 FEET EARLY
SATURDAY. WILL NEED TO KEEP AN EYE ON EXACTLY WHERE THE PSCZ WILL
FORM BECAUSE THERE IS A DISTINCT POSSIBILITY THAT SNOQUALMIE PASS
COULD RECEIVE LOW END ADVISORY CRITERIA SNOWFALL AMOUNTS /6 OR 7
INCHES/ ON SATURDAY.

OTHER THAN THE SNOW IN THE MOUNTAINS...ANTICIPATE GUSTY WINDS
AHEAD OF AND WITH THE OCCLUDED FRONT THAT WILL SWEEP ACROSS LATE
TODAY THROUGH THIS EVENING. A WIND ADVISORY WAS ISSUED FOR THE
MORE WIND PRONE AREAS...NAMELY THE COAST AND PARTS OF THE
NORTHWEST INTERIOR.

THE UPPER TROF WILL MOVE ACROSS THE REGION SATURDAY MORNING BUT
EMBEDDED DISTURBANCES WITHIN THE STRONG WESTERLY FLOW WILL SERVE
TO KEEP WEATHER CONDITIONS UNSETTLED ACROSS THE CWA ON SATURDAY.
THE BEST CHANCE OF PRECIP WILL BE OVER THE MOUNTAINS...COAST...AND
WITHIN THE PSCZ.

THERE MAY BE A BRIEF BREAK IN THE ACTION SATURDAY EVENING BETWEEN
SYSTEMS BUT CANNOT COMPLETELY COUNT ON IT. THE NEXT SYSTEM WILL
QUICKLY FOLLOW ON THE HEELS OF THE DEPARTING ONE...WITH STEADY
PRECIP REDEVELOPING SATURDAY NIGHT. THIS NEXT SYSTEM WILL BE A
FAST ONE...THUS EXPECT THE COLD OR OCCLUDED FRONT TO SWEEP ACROSS
THE CWA LATE SUNDAY MORNING OR EARLY SUNDAY AFTERNOON. SHOWERY
CONDITIONS SHOULD PREVAIL SUNDAY AFTERNOON IN THE WAKE OF THE
FRONT. THE CASCADES ABOVE 3500 FEET CAN EXPECT TO RECEIVE ANOTHER
9 TO 15 INCHES OF NEW SNOW FROM THIS SYSTEM.

.LONG TERM...
CONFIDENCE IN THIS PERIOD WAS NOT HIGH DUE TO LACK OF AGREEMENT
BETWEEN THE MEDIUM RANGE SOLUTIONS AS WELL AS LACK OF RUN TO RUN
CONSISTENCY IN THE MODELS. EITHER THERE WILL BE AN UPPER TROF OVER
THE REGION ON WED OR AN UPPER RIDGE. DECIDED TO LEAVE THE INHERITED
FORECAST PRETTY MUCH INTACT.

&&

.HYDROLOGY...
RIVER FLOODING IS NOT EXPECTED THE NEXT 7 DAYS.

&&

.AVIATION...WESTERLY FLOW ALOFT AS A STRONG FRONTAL SYSTEM
APPROACHES THE COAST. THE AIR MASS IS MOIST AND STABLE EXCEPT FOR
ISOLATED SHOWERS NORTH PART. RAIN FROM THE APPROACHING FRONT WILL
SPREAD INLAND AROUND 15Z. THE FRONT WILL REACH THE COAST AROUND 00Z
AND PUGET SOUND AROUND 04Z. AT THE SURFACE STRONG GUSTY SOUTHEAST
WINDS WILL DEVELOP ALONG THE COAST AND OVER PARTS OF THE NORTH
INTERIOR THIS AFTERNOON AND CONTINUE INTO THE EVENING.

CEILINGS ARE GENERALLY VFR 4K-6K FT. CEILINGS WILL FALL TO MVFR
2K-3K FT IN RAIN 12Z-15Z AND STAY THERE ALL DAY. CEILINGS WILL NOT
IMPROVE MUCH TONIGHT IN ONSHORE SURFACE FLOW AND A SHOWERY PATTERN.

KSEA...DISCUSSION ABOVE APPLIES. WINDS SOUTHEAST 5-9 KT. RAIN AND
MVFR CONDITIONS WILL PREDOMINATE TODAY. WINDS WILL RISE TO SOUTHERLY
8-12 KT IN THE AFTERNOON. CHB

&&

.MARINE...A STRONG FRONTAL SYSTEM WILL MOVE THROUGH THE AREA TODAY.
GALE WARNINGS ARE UP FOR THE COASTAL WATERS AND THE EAST ENTRANCE
AND NORTH INLAND WATERS WITH SMALL CRAFT ADVISORIES ELSEWHERE.
FRONTAL PASSAGE ALONG THE COAST SHOULD BE AROUND 00Z...THEN AROUND
04Z OVER PUGET SOUND. A WESTERLY PUSH BEHIND THE FRONT WILL PRODUCE
SMALL CRAFT ADVISORY WEST WINDS THROUGH THE STRAIT...THOUGH A BRIEF
GALE IS ALSO POSSIBLE.

ANOTHER SYSTEM ON SUNDAY IS GAINING STRENGTH IN THE MODELS. THIS
COULD GIVE GALES ON THE COAST AND DOWN THE STRAIT. SWELLS IN THE
15-20 FOOT RANGE ARE FORECAST TO REACH THE COAST SUNDAY. CHB

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WIND ADVISORIES ARE IN EFFECT FOR THE COAST AND PARTS OF THE
     NORTHWEST INTERIOR.

     WINTER WEATHER ADVISORY IN EFFECT FOR THE CASCADES ABOVE 3500
     FEET FROM 10 AM UNTIL 6 AM SATURDAY.

PZ...GALE WARNING IN EFFECT UNTIL 10 PM TONIGHT FOR THE COASTAL
     WATERS...EAST ENTRANCE TO THE STRAIT OF JUAN DE FUCA...AND
     THE NORTHERN INLAND WATERS.

     SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE REMAINING WATERS.

     SMALL CRAFT ADVISORY IN EFFECT FOR ROUGH BAR UNTIL 10 AM
     SATURDAY FOR THE GRAYS HARBOR BAR.

&&

$$

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