High Surf Advisory 5, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
910 PM PST WED NOV 23 2011

CORRECTED AVIATION AND MARINE

.SYNOPSIS...ANOTHER STRONG FRONT WILL BRING MORE RAIN...MOUNTAIN
SNOW...AND WIND TO PARTS OF WESTERN WASHINGTON ON THANKSGIVING DAY
THROUGH FRIDAY MORNING.  THEN...YET ANOTHER FRONT WILL BRING ANOTHER
ROUND OF RAIN AND WIND OVER THE WEEKEND.  DRY WEATHER IS POSSIBLE
NEXT TUESDAY BEFORE ANOTHER FRONT ARRIVES.

&&

.SHORT TERM...CONVERGENCE ZONE DEVELOPED FOR A PERIOD OF TIME THIS
EVENING BUT IS CURRENTLY DISSIPATING AND THE SHOWERS ARE RETREATING
NORTH.   A FEW MORE SHOWERS OFFSHORE WILL ROLL ACROSS THE AREA
TONIGHT BUT THEY ARE RATHER LIGHT AND NOT NEWS WORTHY.

EYES FOCUSING ON THE NEXT IN THE SERIES OF FRONTAL SYSTEM TO AFFECT
THE PACIFIC NORTHWEST.  THIS SYSTEM IS CURRENTLY OUT NEAR 140W AND
THE LOW CENTER ITSELF WILL SWING TO THE NORTHEAST ACROSS THE
NORTHERN TIP OF VANCOUVER ISLAND.  THE LOW WILL DIRECT A RATHER
STRONG COLD FRONT ACROSS THE AREA DURING THE AFTERNOON HOURS
TOMORROW.  MODELED 925 MB WINDS EXCEED 55KT ALONG THE COAST WITH
GUSTY SURFACE WINDS EXPECTED.  ALREADY HAVE A WIND ADVISORY IN
AFFECT FOR THE COAST BUT HAVE DECIDED TO ELEVATE THAT TO A HIGH WIND
WARNING THIS EVENING WITH THE THOUGHT THAT IT WILL BE A LOW END
WARNING EVENT.

WE HAVE A WIND ADVISORY IN EFFECT FOR THE NORTHWEST INTERIOR FOR
SOUTHEAST WINDS IN ADVANCE OF THE FRONT AND WHILE THERE MAY BE A FEW
LOCATIONS PUSHING CLOSE TO WARNING CRITERIA I BELIEVE AN ADVISORY
COVERS THE SITUATION WELL THERE AND WILL LEAVE IT BE.

THE NEXT PROBLEM TO DEAL WITH IS THE POTENTIAL SNOWFALL WITH THIS
SYSTEM FOR THE MOUNTAIN...NOT THAT I IMAGINE THAT IS A PROBLEM FOR
THE SKI RESORTS.  AIR MASS IS COLD ENOUGH FOR SNOW LEVELS REMAINING
BELOW 3000 FEET THROUGH THE EVENT FOR A GOOD FOOT OR SO OF SNOWFALL
AT PASS LEVEL LATE THURSDAY THROUGH THURSDAY NIGHT.  A WINTER STORM
WARNING IS ALREADY IN EFFECT FOR THIS ASPECT OF THE STORM.

SHOWERS AND MOUNTAIN SNOW WILL DECREASE FRIDAY MORNING WITH A DRY
PERIOD POSSIBLE FOR MUCH OF THE AREA LATER FRIDAY AND FRIDAY NIGHT.
POPS WERE REMOVED FOR MUCH OF THE FORECAST AREA WHILE WE ARE BETWEEN
SYSTEMS.

MODELS GENERALLY AGREE ON LIFTING A MOIST WARM FRONT ACROSS WESTERN
WASHINGTON SATURDAY SPREADING RAIN ACROSS THE AREA.  THERE IS SOME
UNCERTAINTY AS TO HOW MUCH RAIN WILL EVENTUALLY FALL WITH THIS
SYSTEM BUT IT DOES LOOK RATHER WET OVER THE WEEKEND.  SEE THE LATEST
HYDRO SECTION FOR DETAILS.  CERNIGLIA

.LONG TERM...FROM PREVIOUS DISCUSSION...IF THE GFS IS CORRECT...A
ROUND OF HEAVY RAIN ON SUNDAY WILL QUICKLY PUSH SE OF THE AREA ON
SUNDAY NIGHT. SOME COLDER AIR WILL FILTER IN FOR A CHANGE OVER TO
SNOW SHOWERS IN THE CASCADES BUT IT DOES NOT LOOK HEAVY OR PROLONGED
AT THIS POINT. THE LATEST GFS/ECMWF BOTH BUILD A RIDGE OVER THE PAC
NW ON MONDAY INTO MONDAY NIGHT FOR WHAT LOOKS LIKE DRY WEATHER.
DECIDED TO REMOVE POPS GIVEN THAT MODELS AGREE ON THIS. THE NEXT
WEAK LOOKING FRONT HAS A TOUGH TIME PUSHING INTO WRN WA ACCORDING TO
THE GFS. HOWEVER...THE ECMWF IS STRONGER AND DOES BRING A FAST
MOVING BUT SHARP TROUGH THROUGH THE AREA WITH PRECIP BY LATER
TUESDAY AND WEDNESDAY. MOST NW FLOW WITH A CHANCE OF RAIN CONTINUES
THROUGH THE MIDDLE OF NEXT WEEK. PERHAPS MORE SNOW IN THE MOUNTAINS
IF THE ECMWF MODEL IS CORRECT. THE GFS IS NOT AS WET OR COLD SO
THERE IS A LOT OF UNCERTAINTY IN THE FORECAST BY NEXT WEEK.  MERCER

&&

.HYDROLOGY...THE UPPER REACHES OF WESTERN WASHINGTON RIVERS HAVE
CRESTED NOW...AND THE CRESTS WILL BE MAKING THEIR WAY DOWNSTREAM
TONIGHT AND THURSDAY. THE EXCEPTION IS THE CHEHALIS RIVER...A
UNIQUELY SLOW MOVING RIVER IN WESTERN WASHINGTON...WHERE THE CREST
WILL MOVE THROUGH THE CENTRALIA AREA AND THURSTON COUNTY LATE
TONIGHT AND THURSDAY MORNING AND THEN DOWNSTREAM THROUGH GRAYS
HARBOR COUNTY THURSDAY AND THURSDAY NIGHT.

WESTERN WASHINGTON WILL EXPERIENCE RELATIVELY DRY WEATHER TONIGHT
AND THURSDAY MORNING. THE NEXT FRONTAL SYSTEM...WHICH WILL MOVE
THROUGH THE FORECAST AREA THURSDAY AFTERNOON THROUGH FRIDAY
MORNING...IS NOT EXPECTED TO BE HYDROLOGICALLY SIGNIFICANT. IN OTHER
WORDS IT WILL NOT RENEW FLOODING. PRECIPITATION AMOUNTS WILL RANGE
FROM 1 TO 2.5 INCHES OVER THE MOUNTAINS BUT THE SNOW LEVEL WILL BE
AROUND 2000 FT...SO IT WILL BE A SNOW PRODUCER RATHER THAN A FLOOD
PRODUCER.

FLOOD WARNINGS FOR THE STILLAGUAMISH NEAR ARLINGTON AND THE PUYALLUP
NEAR ORTING WILL COME TO AN END THIS EVENING.

FLOOD WARNINGS REMAIN IN EFFECT FOR THE SKOKOMISH...NEWAUKUM...AND
CHEHALIS RIVER AT PORTER.

IN ADDITION THE FLOOD WATCH REMAINS IN EFFECT FOR LEWIS AND THURSTON
COUNTIES. THE FLOOD WATCH COVERS THE POSSIBILITY OF MINOR FLOODING
ON THE REACH OF THE CHEHALIS IN CENTRALIA AND GRAND MOUND AS THE
CREST MOVES THROUGH.

LOOKING FURTHER AHEAD...ANOTHER FRONTAL SYSTEM WILL MOVE THROUGH THE
AREA OVER THE WEEKEND. ITS WARM FRONT WILL BRING SIGNIFICANT
PRECIPITATION TO VANCOUVER ISLAND FRIDAY NIGHT THROUGH SATURDAY
NIGHT...BUT THE HEAVIEST RAIN WILL MISS OUR FORECAST AREA. THE
SYSTEM WILL WEAKEN AS IT MOVES EASTWARD ACROSS WESTERN WASHINGTON
SATURDAY NIGHT THROUGH SUNDAY NIGHT. WE WILL NEED TO PAY ATTENTION
TO THIS FEATURE OVER THE NEXT FEW DAYS...BUT AT THIS TIME IT APPEARS
THAT IT WILL NOT RENEW FLOODING EXCEPT PERHAPS ON THE SKOKOMISH
RIVER.

A FINAL NOTE ABOUT LANDSLIDES...THE USGS LANDSLIDE GUIDANCE
INDICATES THAT LANDSLIDES WILL BE POSSIBLE IF MODERATE TO HEAVY
RAIN OCCURS. SPECIAL WEATHER STATEMENTS COULD BE ISSUED OVER THE
NEXT FEW DAYS TO ADDRESS THAT THREAT.   MCDONNAL/FELTON

&&

.AVIATION...LINGERING PSCZ WILL END BY MIDNIGHT. THERE ARE AREAS OF
CLEARING...MAINLY ARND THE SAN JUANS AND NORTH OF BVS AND ALSO SOUTH
OF SEATTLE AS WELL AS ALONG THE COAST. THE AIR MASS WILL STABILIZE.
SW FLOW ALOFT WILL INCREASE THROUGH THURSDAY AS A STRONG FRONT
PUSHES THROUGH WESTERN WA IN THE AFTERNOON. THIS FRONT WILL BE
STRONG BUT MOVE QUICKER THAN THE LAST ONE...IT WILL BE COOLER...AND
NOT AS WET...BUT MVFR CIGS AND VSBY A GOOD BET THU AFTERNOON AND
EVENING THEN SOME CLEARING BEHIND THE FRONT XCP FOR THE PSCZ AREA
AND THE WEST SLOPES OF THE CASCADES THU NITE. WINDS AT 5000 FT
INCREASE TO 60 KT WITH THE FRONT AND THE STRONG FLOW ALF AND STRONG
PRES GRADIENTS WILL GIVE AREAS OF SLY WINDS GREATER THAN 30 KNOTS BY
THU AFTERNOON. 19

KSEA...REMNANTS OF PSCZ TONIGHT...WE MAY SEE SOME CLEARING AFTER
MIDNIGHT WORK UP FROM THE SOUTH BUT THU WILL BE CLOUDY AGAIN AS THE
WARM ADVECTION KICKS IN AND STRONG SSW FLOW ALF DEVELOPS WITH RAIN
AT TIMES BY AFTERNOON THRU EVENING. WILL PROBABLY REWORK THE TAF A
BIT FOR 06Z.

&&

.MARINE...STRONG COLD FRONT ASSOCIATED WITH A DEEP 970-975 MB LOW
WHICH MOVES THRU QUEEN CHARLOTTE SOUND EARLY THU AFTERNOON. THE
FRONT PUSHES THRU WRN WA LATE THU AFTERNOON. GALE AND STORM WARNINGS
ALREADY IN PLACE AND NO BIG FCST CHANGES EXPECTED TNGT. STRONG POST
FRONTAL ONSHORE FLOW WILL FOLLOW THE FRONT WITH GALE FORCE
WESTERLIES IN THE CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA THU
NITE. A STRONG WARM FRONT WITH AREAS OF GALE FORCE WINDS WILL LIFT
NORTH ACROSS THE COASTAL WATERS FRIDAY NIGHT AND INTO EARLY
SATURDAY. THIS FRONT WILL BRUSH THE NORTHERN WATERS OF THE INTERIOR
OF WESTERN WASHINGTON AS WELL. A COLD FRONT WILL FOLLOW ON SUNDAY
AND MAY PRODUCED MORE GALES...ESPECIALLY IN THE COASTAL WATERS.

SEAS WILL BUILD TO OVER 20 FEET IN THE COASTAL WATERS THURSDAY AND
CONTINUE IN SWELL THURSDAY NIGHT. ANOTHER PERIOD OF SEAS NEARING 20
FT IS LIKELY SATURDAY INTO SUNDAY. 19

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...HIGH WIND WARNING THURSDAY FOR THE NORTH AND CENTRAL COAST.
     WIND ADVISORY NORTH INTERIOR ON THURSDAY.
    .WINTER STORM WARNING NORTH AND CENTRAL CASCADES THURSDAY
     THROUGH FRIDAY MORNING.
    .WINTER WEATHER ADVISORY FOR THE OLYMPICS THURSDAY THROUGH
     THURSDAY NIGHT.
    .FLOOD WATCHES AND WARNINGS REMAIN IN EFFECT FOR PARTS OF
     WESTERN WASHINGTON.
PZ...STORM WARNING COASTAL WATERS LATE TONIGHT THROUGH
     THURSDAY.
    .GALE WARNING STRAIT...NORTHERN INLAND WATERS AND ADMIRALTY
     INLET THURSDAY.
    .SMALL CRAFT ADVISORY COASTAL WATERS AND WEST ENTRANCE TO
     THE STRAIT OF JUAN DE FUCA FOR HAZARDOUS SEAS THROUGH TONIGHT.
    .SMALL CRAFT ADVISORY CENTRAL AND EAST ENTRANCE STRAIT OF JUAN
     DE FUCA THIS EVENING.
    .SMALL CRAFT ADVISORY GRAYS HARBOR BAR FOR SEVERE BAR CONDITIONS.

YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML.

WWW.WEATHER.GOV/SEATTLE