Gale Watch 7, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
320 AM PST WED JAN 27 2016

.SYNOPSIS...A WARM FRONT WILL LIFT NORTHWARD ACROSS THE AREA THIS
MORNING. A VIGOROUS COLD FRONT WILL MOVE EAST ACROSS THE AREA
THURSDAY MORNING...BRINGING A PERIOD OF HEAVY RAIN TO THE OLYMPIC
PENINSULA AND NORTH CASCADES TONIGHT INTO THURSDAY MORNING. ANOTHER
FRONT WILL QUICKLY SWEEP ACROSS WESTERN WASHINGTON ON FRIDAY. STRONG
ONSHORE FLOW WILL GIVE WINDY CONDITIONS...SHOWERS...AND MOUNTAIN
SNOW TO THE AREA FRIDAY NIGHT THROUGH SATURDAY OR SATURDAY NIGHT.
AN UPPER TROUGH ALONG THE U.S. WEST COAST WILL BRING COOL AND
SOMETIMES SHOWERY WEATHER TO THE PACIFIC NORTHWEST SUNDAY THROUGH
EARLY NEXT WEEK.

&&

.SHORT TERM...RADAR AND SATELLITE IMAGERY SHOW A WARM FRONT OVER
SOUTHERN PORTIONS OF WESTERN WASHINGTON THAT WILL LIFT NORTHWARD
ACROSS THE AREA THIS MORNING. THE AIR MASS IS INCREASINGLY MILD AND
MUGGY AS THIS FRONT LIFTS NORTH WITH TEMPERATURES ALREADY IN THE
LOWER 50S IN MANY AREAS OF THE SOUTH INTERIOR AND DEWPOINTS RISING
TO AROUND 50. A VIGOROUS COLD FRONT SITS FROM 50N 135W SOUTH AND
WEST INTO THE PACIFIC. THIS FRONT HAS TAPPED INTO AN SUBTROPICAL
MOISTURE TAP THAT EXTENDS TO NW OF THE HAWAIIAN ISLANDS. RAIN WILL
GRADUALLY INCREASE ALONG THE COAST TODAY AS THE FRONT MOVES INTO THE
WASHINGTON OFFSHORE WATERS AND FLOW ALOFT INCREASES FROM THE SSW.
TEMPERATURES FROM ABOUT EVERETT SOUTH AND EAST IN THE LOWLANDS WILL
BE QUITE MILD TODAY WITH HIGHS GETTING INTO THE UPPER 50S TO AROUND
60. SOME LOWER 60S ARE POSSIBLE MIDDAY IN THE EAST PUGET SOUND
LOWLANDS AS EASTERLY PRESSURE GRADIENTS GIVE SOME DOWNSLOPE OFF THE
CASCADES.

THE COLD FRONT WILL MOVE INTO THE COASTAL WATERS TONIGHT. 850 MB
FLOW INCREASES TO SSW 50-70 KT OVERNIGHT. THIS WILL GIVE A 12-18
HOUR PERIOD OF VERY HEAVY RAINFALL TO THE SOUTH AND SOUTHWEST FACING
OLYMPICS AND TO THE NORTH CASCADES WITH SNOW LEVELS AROUND 8000
FEET. FLOOD WATCHES HAVE BEEN EXPANDED FOR TONIGHT TO
WHATCOM...SKAGIT...SNOHOMISH...AND GRAYS HARBOR COUNTIES IN ADDITION
TO MASON COUNTY THAT WAS ALREADY IN THE WATCH. SEE THE HYDROLOGY
SECTION BELOW FOR MORE DETAILS. STRONG WINDS ALOFT INTERACTING WITH
THE TERRAIN COMBINED WITH THE RELEASE OF LATENT HEAT AS MOISTURE GET
SCOURED OUT BY THE MOUNTAINS WILL RESULT IN A VIGOROUS MESOLOW
FORMING TO THE NORTHEAST OF THE OLYMPICS. CONDITIONS ON THE COAST
AND IN THE NORTH INTERIOR FROM THE ADMIRALTY INLET AREA WILL SEE
WINDY CONDITIONS OVERNIGHT. WHILE FORECAST WINDS ARE 20-30 MPH WITH
GUSTS TO 40 MPH AT THIS TIME...THERE IS A CHANCE THAT A WIND
ADVISORY WILL BE REQUIRED FOR THESE AREAS TONIGHT. WILL LET THE DAY
SHIFT TAKE A LOOK AT THE 12Z MODELS TO REFINE WIND FORECASTS.

THE FRONT MOVES EAST OF THE AREA MIDDAY THURSDAY ALLOWING RAIN TO
TAPER TO SHOWERS AND WINDS TO DIMINISH. SNOW LEVELS IN THE MOUNTAINS
WILL FALL TO AROUND 4000 FEET BY LATE THURSDAY AFTERNOON.

A BRIEF BREAK IN SHOWER ACTIVITY IS EXPECTED LATER THURSDAY NIGHT AS
ONSHORE FLOW DECREASES. THE DECREASE IN ONSHORE FLOW IS IN RESPONSE
TO RAPID DEEPENING OF A LOW 47N 132W THAT CURLS NE TO THE QUEEN
CHARLOTTE SOUND AND AN INSTANT OCCLUSION TO THE SE OF THIS LOW LIFTS
NEWD ACROSS THE OREGON OFFSHORE WATERS.  PRECIPITATION WILL MOVE
BACK INTO THE AREA FROM THE SOUTHWEST FRIDAY MORNING AS THE
OCCLUSION LIFTS NE ACROSS THE AREA. FOLLOWING THE OCCLUSION...EXPECT
STRONG ONSHORE FLOW TO DEVELOP LATER FRIDAY AFTERNOON. SNOW LEVELS
IN THE MOUNTAINS WILL LOWER TO 2500-3500 FEET BY LATE FRIDAY
AFTERNOON. ALBRECHT

.LONG TERM...STRONG ONSHORE FLOW WILL CONTINUE FRIDAY NIGHT INTO
SATURDAY OR SATURDAY NIGHT. THE STRONG ONSHORE FLOW WILL GIVE WINDY
CONDITIONS TO THE AREA ALONG WITH POSSIBLY HEAVY MOUNTAIN SNOW AS
SNOW LEVELS FALL TO AROUND 2500 FEET. SHOWERS...WIND...AND MOUNTAIN
SNOW WILL GRADUALLY DIMINISH LATE SATURDAY NIGHT INTO SUNDAY AS A
DEEP WEST COAST TROUGH DEVELOPS. SNOW LEVELS LATE IN THE WEEKEND
INTO EARLY NEXT WEEK WILL BE LOW...1000-1500 FEET...BUT SHOWERS WILL
BE ON THE DECREASE. ALBRECHT

&&

.AVIATION...A WARM FRONTAL WAVE THIS MORNING WILL PRODUCE SPOTTY
LIGHT RAIN. STRONG SW FLOW WILL DEVELOP TODAY THROUGH TONIGHT AS A
STRONG FRONT SLOWLY PUSHES ACROSS THE AREA. STABLE ATMOSPHERE AND
MOIST AT ALL LEVELS.

A MIX OF MVFR AND LOW VFR THIS MORNING AS STRONGER FLOW ALOFT AND
SOME MIXING IS HELPING TO KEEP CIGS UP A BIT ACROSS THE AREA. THE
EXCEPTION IS THE KCLM TERMINAL WHERE 1/4SM FG PREVAILS BUT SHOULD
BREAK UP AS THE FRONT APPROACHES LATER THIS MORNING. SOME
IMPROVEMENT BEFORE THE MAIN FRONT ARRIVES IS POSSIBLE MIDDAY TO
EARLY AFTERNOON WITH MOSTLY VFR CIGS. HOWEVER...MVFR CONDITIONS ARE
LIKELY TO DEVELOP AGAIN BY EVENING AS STEADY HEAVIER RAIN PICKS UP
WITH THE FRONT OVERNIGHT.

KSEA...SOUTH TO SOUTHEAST WIND 8-12 KT INCREASING TO 10-13 KT W/
GUSTS TO 22 KT THIS AFTERNOON AND EVENING. CIGS ARE TRICKY THIS
MORNING AS A WEAK WAVES IS BRINGING SOME LIGHT RAIN AND ALSO HELPING
TO MIX SOME LOW CLOUDS OUT WITH INCREASING FLOW ALOFT. PERIODS OF
MVFR OR LOW VFR IS EXPECTED WITH MOSTLY LOW VFR MIDDAY. MVFR SHOULD
DEVELOP AGAIN TONIGHT WITH THE HEAVIER RAINFALL.

&&

.MARINE...MODELS HAVE TRENDED A BIT STRONGER WITH THE FRONT WHICH
WILL ENTER THE COASTAL WATERS LATER TODAY...THEN PUSH THROUGH THE
INLAND WATERS OVERNIGHT. GALES WARNINGS REMAIN IN EFFECT FOR MOST
THE WATERS EXCEPT FOR THE CENTRAL STRAIT...ADMIRALTY INLET...AND
PUGET SOUND. HIGH-END SMALL CRAFT WINDS TO 30 KT OUT OF THE SE ARE
STILL ANTICIPATED IN ADMIRALTY INLET. A BRIEF PERIOD OF ONSHORE FLOW
WILL FOLLOW THE FRONT THURSDAY.

ANOTHER STRONG LOW PRESSURE SYSTEM WILL MOVE NE ACROSS THE AREA
FRIDAY. WESTERLY GALES ARE LIKELY OVER THE COASTAL WATERS AND IN THE
CENTRAL STRAIT AND EAST ENTRANCE STRAIT...WITH SMALL CRAFT ADVISORY
WINDS FOR THE REMAINING WATERS. ONSHORE FLOW WILL CONTINUE
SATURDAY...THEN EASE AND TURN MORE NORTHERLY ON SUNDAY.

WESTERLY SWELL OF 10-15 FEET WITH A PERIOD OF 14 TO 16 SECONDS WILL
CONTINUE OVER THE COASTAL WATERS TODAY. A LARGER SWELL TRAIN OF 18
TO 22 FT WILL ARRIVE TONIGHT...SUBSIDING SLIGHTLY TO 17 TO 19 FEET
THURSDAY. A HIGH SURF ADVISORY IS IN EFFECT FOR THE NORTH AND
CENTRAL COAST...SPECIFICALLY ADDRESSING THE POSSIBLE BEACH EROSION
AROUND THE OCEAN SHORES NORTH JETTY. MODELS NOW SHOW A POSSIBLE
LARGER SWELL TRAIN OF 20-25 FEET POSSIBLY ARRIVING BY LATE FRIDAY
NIGHT AND SATURDAY. THIS COULD EXASPERATE COASTAL EROSION PROBLEMS
ALONG THE WASHINGTON COAST. DTM

&&

.HYDROLOGY...THE STRONG FRONT MOVING THROUGH THE AREA LATE THIS
AFTERNOON THROUGH MIDDAY THURSDAY WILL PRODUCE 3-6 INCHES OF RAIN IN
THE OLYMPICS AND 2 TO 4 INCHES IN THE NORTH CASCADES. MUCH OF THE
RAINFALL WILL COME IN 12-18 HOURS AND WILL FALL WITH SNOW LEVELS
NEAR OR OVER 8000 FEET. BASED ON THE HEAVY BURST OF RAINFALL AND
EARLIER RIVER FORECASTS ISSUED BY THE RIVER FORECAST CENTER IN
PORTLAND OREGON THAT SHOW SEVERAL RIVERS COMING VERY CLOSE TO OR
HITTING FLOOD STAGE...HAVE OPTED TO EXPAND THE FLOOD WATCH FOR
PORTIONS OF THE AREA TONIGHT INTO THURSDAY NIGHT. THE FLOOD WATCHES
NOW INCLUDE MASON...GRAYS HARBOR...SNOHOMISH...SKAGIT...AND WHATCOM
COUNTIES. THE SKOKOMISH RIVER IN MASON COUNTY IS VERY LIKELY TO
FLOOD AND MAY REACH MAJOR FLOOD STAGE LATE TONIGHT OR THURSDAY
MORNING. OTHER RIVERS LIKE THE STILLIGUAMISH...SKAGIT...AND NOOKSACK
RIVERS WILL COME VERY CLOSE TO FLOOD STAGE ON THURSDAY AND MAY
FLOOD. THE SATSOP RIVER IS NOT CURRENTLY EXPECTED TO FLOOD...BUT
WITH UP TO 6 INCHES OF RAINFALL ON THE SOUTH SLOPES OF THE OLYMPICS
TONIGHT INTO EARLY THURSDAY...IT WILL NEED TO BE WATCHED.

OTHER RIVERS IN WESTERN WASHINGTON ARE NOT EXPECTED TO FLOOD WITH
THIS ATMOSPHERIC RIVER EVENT.

SNOW LEVELS WILL FALL TO BELOW 3000 FEET BY FRIDAY NIGHT OR SATURDAY
AND PRECIPITATION WILL BECOME MORE SHOWERY. OUTSIDE OF THE WATCH
AREA...RIVERS ARE NOT EXPECTED TO FLOOD FOR THE NEXT 7 DAYS. ALBRECHT

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WATCH FROM THIS EVENING THROUGH LATE THURSDAY NIGHT FOR
     THE FOLLOWING COUNTIES IN WESTERN WASHINGTON...MASON...GRAYS
     HARBOR...SNOHOMISH...SKAGIT...WHATCOM.

     HIGH SURF ADVISORY FROM 4 PM THIS AFTERNOON TO 4 AM PST THURSDAY
     FOR CENTRAL COAST-NORTH COAST.

PZ...SMALL CRAFT ADVISORY FOR ROUGH BAR UNTIL 10 AM PST THURSDAY FOR
     GRAYS HARBOR BAR.

     GALE WARNING UNTIL 4 AM PST THURSDAY FOR COASTAL WATERS FROM
     CAPE FLATTERY TO JAMES ISLAND 10 TO 60 NM-COASTAL WATERS
     FROM CAPE FLATTERY TO JAMES ISLAND OUT 10 NM-COASTAL WATERS
     FROM JAMES ISLAND TO POINT GRENVILLE 10 TO 60 NM-COASTAL
     WATERS FROM JAMES ISLAND TO POINT GRENVILLE OUT 10 NM-
     COASTAL WATERS FROM POINT GRENVILLE TO CAPE SHOALWATER 10
     TO 60 NM-COASTAL WATERS FROM POINT GRENVILLE TO CAPE
     SHOALWATER OUT 10 NM.

     SMALL CRAFT ADVISORY UNTIL NOON PST TODAY FOR EAST ENTRANCE U.S.
     WATERS STRAIT OF JUAN DE FUCA-NORTHERN INLAND WATERS
     INCLUDING THE SAN JUAN ISLANDS.

     GALE WARNING FROM NOON TODAY TO 3 AM PST THURSDAY FOR EAST
     ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA-NORTHERN INLAND
     WATERS INCLUDING THE SAN JUAN ISLANDS.

     GALE WARNING UNTIL 3 AM PST THURSDAY FOR WEST ENTRANCE U.S.
     WATERS STRAIT OF JUAN DE FUCA.

     SMALL CRAFT ADVISORY UNTIL 6 AM PST THURSDAY FOR ADMIRALTY INLET.

&&

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