Flood Watch 6, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 AM PST SAT MAR 12 2011

.SYNOPSIS...THE NEXT PACIFIC STORM WILL MOVE THROUGH WESTERN
WASHINGTON TODAY...WITH PRECIPITATION TAPERING TO SHOWERS BEHIND THE
FRONT THIS AFTERNOON. A STRONGER SYSTEM WILL AFFECT THE AREA LATE
TONIGHT THROUGH MONDAY...RESULTING IN WINDY CONDITIONS AS WELL AS
MORE RAIN AND MOUNTAIN SNOW. THE WEATHER WILL REMAIN UNSETTLED INTO
NEXT WEEK.

&&

.SHORT TERM...THE NEXT FRONTAL SYSTEM IS MOVING INTO THE PACIFIC
NORTHWEST EARLY THIS MORNING...WITH RAIN SPREADING INTO WESTERN
WASHINGTON. AMONG THE SYSTEMS IN THE CURRENT SERIES...THIS FRONT IS
A RELATIVELY WEAK ONE. ITS PARENT LOW -- SURFACE AND ALOFT -- IS
LOCATED JUST SOUTH OF HAIDA GWAII NEAR 52N/135W AND TRACKING NORTH.

NOT SURPRISINGLY...MODELS AGREE THAT THE FRONT WILL WEAKEN AS IT
MOVES INLAND TODAY. AND IN FACT THE RAINFALL IN THE FRONTAL BAND
ALREADY HAS LOTS OF HOLES IN IT. MORE OR LESS STEADY RAIN THIS
MORNING SHOULD GIVE WAY TO SCATTERED SHOWERS THIS AFTERNOON AS THE
FRONT MAKES ITS WAY INTO THE CASCADES. THE RELATIVELY WEAK
POST-FRONTAL WESTERLIES AND MINOR SURFACE RIDGING COULD BRING SOME
SUN BREAKS THIS AFTERNOON AS WELL. THE SNOW LEVEL IN THE MOUNTAINS
WILL BE NEAR 2500 FT TODAY WITH SNOWFALL RANGING FROM 1 TO 5 INCHES.

ANOTHER STRONGER FRONTAL SYSTEM WILL AFFECT WESTERN WASHINGTON LATER
TONIGHT THROUGH MONDAY. RAIN WILL SPREAD ACROSS THE FORECAST AREA
FROM THE SOUTHWEST LATER TONIGHT AND SUNDAY MORNING. THE OCCLUDED
FRONT...WHICH WILL LIKELY BE ACCOMPANIED BY 850 MB WINDS OF 60 KT OR
MORE...WILL MOVE THROUGH FROM THE SOUTHWEST SUNDAY AFTERNOON AND
EVENING. THEN A POST-FRONTAL TROUGH -- OR MORE LIKELY THE BENT BACK
PORTION OF THE OCCLUSION -- WILL SWING THROUGH FROM THE WEST ON
MONDAY.

THE SURFACE FRONTS WILL BRING WINDY CONDITIONS ESPECIALLY TO THE
COAST AND NORTHWEST INTERIOR. PROBABLY WE WILL REMAIN BELOW HIGH
WIND WARNING CRITERIA -- SUSTAINED WINDS 40 MPH OR GUSTS 60 MPH --
BUT WIND ADVISORIES MAY BE NEEDED IN AREAS.

STORM TOTAL PRECIPITATION -- FROM LATE TONIGHT THROUGH MONDAY NIGHT
-- WILL BE SOMETHING LIKE 3 TO 6 INCHES IN THE OLYMPIC MOUNTAINS.
EVEN THOUGH THAT WILL BE SNOW AT HIGHER ELEVATIONS...IT SHOULD BE
ENOUGH TO DRIVE THE SKOKOMISH RIVER ABOVE FLOOD STAGE. RAINFALL ALONG
THE COAST WILL BE 1 TO 2.5 INCHES...WITH AROUND 0.50 TO 1.50 INCHES
OVER THE INTERIOR LOWLANDS.

THE SNOW LEVEL WILL RISE TO 4000 TO 5000 FT WITH THE OCCLUDED FRONT
ON SUNDAY...THEN FALL TO AROUND 2500 FT AGAIN ON MONDAY. MOUNTAIN
SPOTS LIKE MT BAKER...PARADISE...AND HURRICANE RIDGE WILL PROBABLY
RECEIVE HIGH-END ADVISORY SNOWFALL -- AND LOW-END WARNING AMOUNTS
ARE POSSIBLE.  MCDONNAL

.LONG TERM...AS WE HAVE BEEN ADVERTISING...THE IMPRESSIVE PARADE OF
STORMS WILL CONTINUE INTO THE LONGER RANGE. YET ANOTHER SYSTEM WILL
BE RIGHT ON THE HEELS OF THE ONE DISCUSSED ABOVE...AFFECTING THE
AREA LATE MONDAY NIGHT THROUGH TUESDAY NIGHT. A LESS ACTIVE
POST-FRONTAL SHOWERY REGIME STILL LOOKS LIKE A GOOD BET WEDNESDAY
THROUGH THURSDAY NIGHT...AND THEN PROBABLY ANOTHER FRONTAL SYSTEM
WILL ARRIVE FRIDAY.  MCDONNAL

&&

.HYDROLOGY...THE FLOOD WARNING FOR THE REACH OF THE CHEHALIS RIVER
IN SOUTHWEST THURSTON COUNTY -- THE CHEHALIS NEAR GRAND MOUND --
ENDED JUST AFTER MIDNIGHT...AND WE ARE CONFIDENT THAT THE LOWER
CHEHALIS RIVER IN GRAYS HARBOR COUNTY WILL REMAIN JUST BELOW FLOOD
STAGE TODAY. THE FRONTAL SYSTEM MOVING THROUGH WESTERN WASHINGTON
TODAY IS RELATIVELY WEAK...AND ITS RAINFALL SHOULD HAVE LITTLE
IMPACT ON RIVERS.

AS DISCUSSED ABOVE...A MUCH STRONGER FRONTAL SYSTEM WILL AFFECT THE
AREA LATE TONIGHT THROUGH MONDAY OR MONDAY NIGHT. TOTAL QPF OVER THE
OLYMPIC MOUNTAINS FOR THAT SYSTEM IS IN THE 3 TO 6 INCH RANGE. EVEN
THOUGH THE SNOW LEVEL WILL NOT BE ESPECIALLY HIGH...THAT SHOULD BE
ENOUGH TO DRIVE THE SKOKOMISH RIVER ABOVE FLOOD STAGE. LATEST NWRFC
GUIDANCE SHOWS THE SKOKOMISH REACHING FLOOD STAGE EARLY MONDAY
MORNING...AND IT COULD HAPPEN EARLIER THAN THAT. THE HYDROLOGIC
OUTLOOK WILL BE UPGRADED TO A FLOOD WATCH WITH THE MORNING PACKAGE.

RIGHT NOW IT LOOKS LIKE ONLY THE EXCEPTIONALLY FLOOD-PRONE SKOKOMISH
RIVER WILL FLOOD. FLOODING LOOKS UNLIKELY ON ANY OTHER RIVER IN OUR
FORECAST AREA...BUT SOME COULD BE CLOSE AND WILL BEAR WATCHING.
CERTAINLY THAT INCLUDES THE CHEHALIS AND SKOOKUMCHUCK RIVERS...WHICH
JUST EXPERIENCED MINOR FLOODING ON THEIR MOST FLOOD-PRONE REACHES.

THE GREEN RIVER IS NOT EXPECTED TO FACE A FLOOD THREAT IN THE NEXT
TEN DAYS.  MCDONNAL

&&

.AVIATION...A COLD FRONT MOVING ONTO THE WASHINGTON COAST THIS
MORNING WILL WEAKEN AS IT MOVES THROUGH THE INLAND WATERS BY MIDDAY.
A WEAK AND BRIEF RIDGE OF HIGH PRES AT THE SURFACE AND ALOFT WILL
MOVE BY THE AREA TO THE SOUTH AND EAST LATER THIS AFTERNOON AND
TONIGHT. A STRONG WARM FRONT WILL APPROACH THE AREA FROM THE
SOUTHWEST ON SUNDAY.

RAIN IS OCCURING THIS MORNING TO THE EAST OF THE INCOMING FRONT AND
THERE IS PRONOUNCED LEE SIDE DRYING TO THE NE OF THE OLYMPIC
PENINSULA. THIS FRONT WILL NOT PUSH THROUGH THE INTERIOR CLEANLY BUT
WILL GRADUALLY WEAKEN AS IT PUSHES E TOWARD THE CASCADES. THIS WILL
MEAN THAT CLOUDS AND MOISTURE WITH THE FRONT WILL ONLY SLOWLY
DECREASE 18Z-23Z. MAINLY VFR CONDITIONS WITH CEILINGS 050-070 ARE
EXPECTED TONIGHT AND EARLY SUNDAY.

KSEA...EXPECT LIGHT RAIN TO MOISTEN THE LOWER LEVELS THIS MORNING
AHEAD OF THE FRONT WITH CEILINGS GRADUALLY LOWERING TO ABOUT 025
AHEAD OF THE FRONT. FROPA WILL BE 16-18Z BUT WILL NOT BE PRONOUNCED
WITH THE FRONT WEAKENING AS IT MOVES THROUGH THE AREA. CONDITIONS
WILL IMPROVE TO VFR BEHIND THE FRONT WITH CIGS IMPROVING TO BKN035
IN SCATTERED SHOWERS. EXPECT SOUTH WINDS 9-13 KT TO DOMINATE THROUGH
TONIGHT. ALBRECHT

&&

.MARINE...A COLD FRONT MOVING ONSHORE EARLY THIS MORNING WILL WEAKEN
AS IT MOVES THROUGH THE INLAND WATERS BY MIDDAY. GALES ARE OCCURRING
ON THE COAST...IN THE NORTHERN INLAND WATERS...AND AT THE EAST
ENTRANCE TO THE STRAIT. EXPECT THESE WINDS TO GRADUALLY DIMINISH
BELOW GALE FORCE BY 18Z AS THE FRONT MOVES THROUGH.

A STRONG WARM FRONT WILL APPROACH THE WATERS FROM THE SOUTHWEST
SUNDAY AND MOVE THROUGH THE AREA LATE SUNDAY AFTERNOON OR SUNDAY
NIGHT. GALES WILL LIKELY DEVELOP SUN MORNING ON THE COAST AND DURING
THE DAY SUNDAY AT THE ENTRANCES TO THE STRAIT AND IN THE NORTHERN
INLAND WATERS. ONCE THE WARM FRONT PASSES...WINDS WILL TURN TO THE
SOUTH BUT REMAIN RATHER STRONG AS A DEEP 975 TO 980 MB LOW CURLS NE
THROUGH THE OFFSHORE WATERS. GALE WATCHES HAVE BEEN ISSUED FOR THE
COASTAL WATERS ON SUNDAY AND MAY NEED TO BE UPGRADED TO WARNINGS OR
EXPANDED EASTWARD LATER THIS MORNING.

THE DEEP LOW SUN NIGHT AND MON MOVES NORTH INTO THE GULF OF ALASKA.
ITS ASSOCIATED BENT BACK OCCLUSION WILL MOVE THROUGH THE WATERS MON
KEEPING GALE CONDITIONS GOING OVER MOST OF THE WATERS. STRONG WEST
WINDS TO THE SOUTH OF THE LOW THAT MOVES INTO THE GULF OF ALASKA SUN
NIGHT INTO MON WILL DEVELOP A LARGE SWELL TRAIN OF 25 TO 30 FT. THE
SWELL WILL DECAY TO NEAR 25 FT AS IT PUSHES ONSHORE ON MONDAY.

ANOTHER STRONG FRONT WILL LIKELY MOVE THROUGH THE WATERS ON TUESDAY.
ALBRECHT

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WARNINGS AND/OR WATCHES ARE IN EFFECT FOR PARTS OF THE
      FORECAST AREA.

PZ...GALE WARNING COAST...ENTRANCES TO THE STRAIT OF JUAN DE
      FUCA...AND NORTHERN INLAND WATERS THROUGH MID MORNING.

     SMALL CRAFT ADVISORY WEST ENTRANCE TO THE STRAIT...CENTRAL
      STRAIT OF JUAN DE FUCA AND ADMIRALTY INLET THROUGH MID
      MORNING.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS COAST AND WEST ENTRANCE
      10 AM PST THIS MORNING THROUGH LATE TONIGHT.

     GALE WATCH COASTAL WATERS SUNDAY INTO MONDAY.

     SMALL CRAFT ADVISORY GRAYS HARBOR BAR FOR ROUGH BAR CONDITIONS.

FOR AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION...PLEASE SEE
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML.