Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 041736
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
936 AM PST THU FEB 4 2016

.UPDATE...REMARKS CONCERNING THE POSSIBILITY OF FLOODING ON THE
SKOKOMISH RIVER HAVE BEEN REVISED. SEE THE HYDROLOGY SECTION FOR
DETAILS.

&&

.SYNOPSIS...A WARM FRONT WILL LIFT SLOWLY NORTHEAST ACROSS WESTERN
WASHINGTON TODAY AND TONIGHT FOR RAIN AT TIMES...AND THE SNOW
LEVEL WILL RISE TO AROUND 5000 FEET TONIGHT. A STRONGER FRONTAL
SYSTEM WILL MOVE THROUGH FRIDAY AFTERNOON AND NIGHT FOR RAINY AND
WINDY WEATHER. SHOWERS WILL LINGER SATURDAY...AND A STRONG UPPER
RIDGE SHOULD BRING DRY MILD WEATHER SUNDAY THROUGH WEDNESDAY.

&&

.SHORT TERM...AN UPPER LEVEL RIDGE IS ALONG THE PACIFIC NORTHWEST
COAST THIS MORNING. MOIST POST-FRONTAL WESTERLY FLOW AT LOWER
LEVELS IS STILL PRODUCING SNOW IN THE MOUNTAINS...WITH THE SNOW
LEVEL BELOW HIGHWAY PASS LEVELS. AT 8 AM IT WAS SNOWING AT PRETTY
MUCH ALL OF THE MOUNTAIN OBSERVATION SITES...AND WE WILL LET THE
WINTER WEATHER ADVISORY FOR THE CASCADES CONTINUE THROUGH NOON. AT
THE SAME TIME A WARM FRONT IMMEDIATELY UPSTREAM OF THE UPPER
RIDGE AXIS IS LIFTING NORTHEAST INTO THE FORECAST AREA...WITH THE
LEADING EDGE OF THE RAIN ALONG A LINE FROM QUILLAYUTE TO
TROUTDALE.

THE UPPER RIDGE WILL BUILD AND SHIFT SLOWLY EAST TODAY AND
TONIGHT...WHILE THE WARM FRONT AND ITS AREA OF PRECIPITATION
LIFTS SLOWLY NORTHEAST. UP TO ANOTHER QUARTER INCH OF RAIN IS
LIKELY IN THE INTERIOR LOWLANDS...WITH A LITTLE MORE AT THE
COAST...AND UP TO 1 INCH PRECIPITATION IN THE MOUNTAINS. THE
ATMOSPHERE IS GOING TO WARM CONSIDERABLY...WITH THE SNOW LEVEL
RISING TO AROUND 5000 FT OVERNIGHT. HIGHS TODAY WILL BE AROUND 50
WITH LOWS TONIGHT IN THE 40S.

A STRONGER AND WARMER FRONTAL SYSTEM WILL MOVE THROUGH THE
FORECAST AREA FRIDAY AND FRIDAY NIGHT. IT WILL BRING WINDY
CONDITIONS TO THE AREA -- ESPECIALLY AT THE COAST AND IN THE NORTH
INTERIOR...WHERE ADVISORY LEVEL WINDS ARE LIKELY AND ONE OR TWO
HIGH WIND REPORTS ARE POSSIBLE.

MODELS AGREE FAIRLY WELL ON THE TIMING OF THIS SYSTEM AND SHOW IT
MOVING THROUGH QUICKLY. THE WARM FRONT WILL LIFT NORTHEAST ACROSS
WESTERN WASHINGTON FRIDAY...WITH THE COLD FRONT MOVING THROUGH
FROM THE WEST LATE FRIDAY AFTERNOON AND EVENING. MODERATE TO
HEAVY PRECIPITATION IS LIKELY WITH THE WARM FRONT AND IN THE WARM
SECTOR...ESPECIALLY ON SOUTHWEST FACING SLOPES OF THE MOUNTAINS
WITH 850 MB WINDS 50 TO 60 KT AND THE SNOW LEVEL REACHING 6000
FT. BUT THAT PERIOD WILL BE BRIEF -- JUST 6 TO 8 HOURS OR SO AND TOTAL
PRECIPITATION WILL PROBABLY BE 0.25 TO 0.75 INCH FOR THE INTERIOR
LOWLANDS...WITH 0.5 TO 1.5 INCHES AT THE COAST...AND 1 TO 2.5
INCHES IN THE MOUNTAINS.

STRONG MOIST WESTERLY FLOW WILL FOLLOW THE FRONT FRIDAY NIGHT...
THEN WEAKEN AND VEER TO NORTHWEST SATURDAY AHEAD OF THE UPPER
RIDGE BUILDING OFFSHORE. SO SHOWERS WILL DECREASE DURING THIS
PERIOD...EVENTUALLY BECOMING LIMITED MAINLY TO THE WEST SLOPES OF
THE MOUNTAINS ON SATURDAY. THE RELATIVELY HIGH SNOW LEVELS WITH
THE WARM FRONT WILL PRECLUDE HEAVY SNOW 5500 FT OR LOWER...WHICH
ARE THE ELEVATIONS WE CONSIDER FOR WINTER STORM WARNINGS AND
ADVISORIES. BUT ADVISORY AMOUNTS ARE CERTAINLY POSSIBLE FRIDAY
NIGHT AND SATURDAY WITH THE LOWER SNOW LEVELS FOLLOWING THE COLD
FRONT. MCDONNAL

.LONG TERM...HERE IS THE LONG TERM SECTION FROM THE EARLY MORNING
FORECAST DISCUSSION -- A HIGH AMPLITUDE UPPER RIDGE IS STILL
ADVERTISED BY MODELS TO BUILD OVER THE WRN U.S. SUNDAY AND PERSIST
THROUGH MID WEEK. THERE IS A SLIGHT CHANCE THAT A WARM FRONT
OFFSHORE BRUSHES THE AREA WITH SOME LIGHT RAIN SUNDAY MORNING BUT
THIS WOULD BE LIMITED TO THE OLYMPIC PENINSULA AND NOT LIKELY TO
REACH INLAND AREAS. CLOUDS WILL DECREASE WITH MOSTLY SUNNY SKIES
BY MONDAY AS THE LOW LEVEL FLOW TURNS OFFSHORE. MODELS SHOW 500 MB
HEIGHTS RISING TO OVER 5800M MONDAY WITH 850 MB TEMPS WARMING TO
AROUND +14C. HIGHS WERE NUDGED UPWARD A BIT WITH UPPER 50S TO
AROUND 60 FORECAST BUT I WOULD NOT BE SURPRISED IF LOW 60S WERE
MORE WIDESPREAD THAN FORECAST OR WHAT MOS INDICATES. HEIGHTS COME
DOWN SLIGHTLY TUESDAY AND WEDNESDAY SO HIGH TEMPERATURES MAY
STRUGGLE TO REACH 60 BUT IT WILL STILL BE A PLEASANT STRETCH OF
SUNNY DRY WEATHER. MERCER

&&

.AVIATION...A TRANSIENT UPPER RIDGE WILL PASS ACROSS WRN WA
TODAY. LIFT AND WARM ADVECTION AT THE PERIPHERY OF THE RIDGE WILL
LEAD TO AREAS OF LIGHT RAIN TODAY...DIMINISHING FOR A TIME THIS
EVNG. A VIGOROUS UPPER LEVEL TROUGH WILL PUSH INTO AND ACROSS WRN
WA ON FRI. MODERATE WEST FLOW ALOFT TODAY...BECOMING STRONG SW
FLOW ON FRI. AREAS OF RAIN TODAY SUPPORTING WIDESPREAD IFR/MVFR
CIGS. AN EASTERLY COMPONENT TO SFC WINDS WILL DEVELOP THIS
EVNG...SETTING UP VFR CONDS THIS EVNG AND OVERNIGHT. FRIDAY`S
STRONG FRONT WILL QUICKLY SPREAD RAIN AND LOWERING CIGS INTO WRN
WA ON FRI MORNING. WHERE SFC WINDS REMAIN LIGHT ON FRI...LOW-LEVEL
WIND SHEAR WILL BE AN ISSUE.

KSEA...LIGHT RAIN SPREADING INTO THE TERMINAL AREA RIGHT
NOW...WITH LIGHT RAIN CONTINUING FOR MOST OF THE AFTN. EXPECT
ENOUGH MOISTENING FOR CIGS TO LOWER BELOW 020 FOR A FEW HOURS
CENTERED AROUND 21Z. RAIN WILL PETER OUT FROM 00Z-06Z...AND A
DRYING EASTERLY COMPONENT WILL DEVELOP TO SFC WIND...WHICH SHOULD
HELP SCATTER OUT LOW CLOUDS AROUND 03Z. ON FRI...EXPECTING A
STRONG FRONT LATE IN THE DAY. IT WILL BE PRECEDED BY LOWERING
CIGS...OCCASIONALLY MODERATE RAIN...AND S-SW WINDS OF 50-60 KNOTS
IN THE 2000-5000 FOOT LAYER.HANER

&&

.MARINE...CURRENTLY IN A RELATIVE WIND LULL BETWEEN YESTERDAY`S
FRONT AND THE NEXT STRONG FRONTAL PASSAGE ON FRI PM. THE NEXT
FRONT WILL BE PRECEDED BY INCREASING S-SE WINDS TONIGHT...WITH
GALES FOR THE COAST...NORTHERN INLAND WATERS...AND BOTH ENTRANCES
TO THE STRAIT ON FRI. FOLLOWING THE FRONT ON FRI NIGHT...LOOKING
FOR WEAKER SW GRADIENTS...BUT IT WILL STILL BE ENOUGH FOR SMALL
CRAFT WINDS THROUGH THE STRAIT...AND AROUND THE SOUTH END OF THE
OLYMPIC MTNS INTO PUGET SOUND.

CURRENT ENERGETIC SWELL TRAIN APPEARS TO BE REACHING THE TAIL END
OF ITS PEAK ALONG THE COAST. SWELL WILL SOON START THE PROCESS OF
SUBSIDING. TIDES ALONG THE COAST WILL ALSO BE FALLING FOR THE REST
OF THE MORNING...SO EXPIRATION OF THE HIGH SURF ADVISORY AT 1 PM
LOOKS GOOD. ANOTHER ROUND OF SWELL IS EXPECTED ON FRI...BUT THE
WAVE PERIOD WILL BE SHORTER AND LESS ENERGETIC...AND THE HIGHEST
WAVES WILL COME NEAR A LOW TIDE ON FRI AFTN...SO NOT EXPECTING
HIGHLIGHTS FOR THAT OCCURRENCE. HANER

&&

.HYDROLOGY...RIVER FLOODING IS POSSIBLE ON THE SKOKOMISH RIVER
FRIDAY NIGHT. OTHERWISE RIVER FLOODING IS NOT EXPECTED THE NEXT 7
DAYS.

THE LATEST MODEL RUNS SHOW SLIGHTLY HIGHER PRECIPITATION AMOUNTS
WITH THE FRONTAL SYSTEM THAT MOVES THROUGH THE AREA FRIDAY AND
FRIDAY NIGHT -- IN THE RANGE OF 1 TO 3 INCHES OVER THE OLYMPIC
MOUNTAINS...AND MOST OF THAT WILL FALL IN LESS THAN 12 HOURS WITH
THE SNOW LEVEL AROUND 6000 FT. THERE IS A POSSIBILITY THAT THIS
WILL BE ENOUGH TO DRIVE THE EXCEPTIONALLY FLOOD-PRONE SKOKOMISH
RIVER ABOVE FLOOD STAGE. THIS AFTERNOON WE WILL DECIDE WHETHER OR
NOT TO ISSUE A FLOOD WATCH FOR THAT AS WELL AS A SPECIAL WEATHER
STATEMENT FOR THE POSSIBILITY OF LANDSLIDES. MCDONNAL

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WINTER WEATHER ADVISORY UNTIL NOON PST TODAY FOR CASCADES OF
     PIERCE AND LEWIS COUNTIES-CASCADES OF SNOHOMISH AND KING
     COUNTIES-CASCADES OF WHATCOM AND SKAGIT COUNTIES.

     HIGH SURF ADVISORY UNTIL 1 PM PST THIS AFTERNOON FOR CENTRAL
     COAST-NORTH COAST.

PZ...SMALL CRAFT ADVISORY FOR ROUGH BAR UNTIL 4 PM PST FRIDAY FOR
     GRAYS HARBOR BAR.

     SMALL CRAFT ADVISORY UNTIL 11 PM PST THIS EVENING 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.

     GALE WARNING FROM 11 PM THIS EVENING TO 4 PM PST FRIDAY 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.

     GALE WARNING FROM 1 AM TO 6 PM PST FRIDAY FOR EAST ENTRANCE U.S.
     WATERS STRAIT OF JUAN DE FUCA.

     GALE WARNING FROM 4 AM TO 6 PM PST FRIDAY FOR NORTHERN INLAND
     WATERS INCLUDING THE SAN JUAN ISLANDS.

     SMALL CRAFT ADVISORY UNTIL 1 AM PST FRIDAY FOR WEST ENTRANCE
     U.S. WATERS STRAIT OF JUAN DE FUCA.

     GALE WARNING FROM 1 AM TO 4 PM PST FRIDAY FOR WEST ENTRANCE U.S.
     WATERS STRAIT OF JUAN DE FUCA.

     SMALL CRAFT ADVISORY FROM 1 AM TO 6 PM PST FRIDAY FOR CENTRAL
     U.S. WATERS STRAIT OF JUAN DE FUCA.

     SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 6 PM PST FRIDAY
     FOR ADMIRALTY INLET.

&&

$$

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