Small Craft Advisory 16, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
236 AM PST WED JAN 20 2016

.SYNOPSIS...AN UPPER RIDGE WILL BRING DRIER WEATHER TO WESTERN
WASHINGTON TODAY WITH A FEW SUN BREAKS. A FRONTAL SYSTEM WILL MOVE
SLOWLY ACROSS THE REGION TONIGHT THROUGH THURSDAY NIGHT...FOR A
PERIOD OF WET WEATHER AND HIGHER SNOW LEVELS. THE FRONT WILL MOVE
EAST FRIDAY...AND A WEAK UPPER TROUGH WILL BE OVER THE AREA THIS
WEEKEND. ANOTHER FRONT SHOULD ARRIVE EARLY NEXT WEEK.

&&

.SHORT TERM...AN UPPER SHORTWAVE MOVED INTO WESTERN WASHINGTON
TUESDAY EVENING FOLLOWING THE FRONTAL SYSTEM MOVING THROUGH...AND
IT MOVED EAST OF THE CASCADES OVERNIGHT. SCATTERED LIGHT SHOWERS
CONTINUE OVER THE FORECAST AREA EARLY THIS MORNING...MAINLY IN
THE PUGET SOUND REGION AND OVER THE WEST SLOPES OF THE CASCADES.
TEMPERATURES AT 2 AM WERE IN THE MID 30S TO MID 40S.

THE COMBINATION OF MOISTURE IN THE LOWER 8000 FT OR SO OF THE
ATMOSPHERE AND LOW LEVEL WESTERLY FLOW WILL KEEP SOME SHOWERS OVER
THE AREA...MAINLY THIS MORNING AND MAINLY OVER THE CASCADES. A
SMALL UPPER RIDGE...PRECEDING THE NEXT FRONTAL SYSTEM UPSTREAM...
WILL MOVE TO THE PACIFIC NORTHWEST COAST TODAY AND INLAND DURING
THE AFTERNOON. THE RIDGE SHOULD BRING SOME CLEARING TO AT LEAST
THE INTERIOR LOWLANDS IN THE AFTERNOON. HIGHS TODAY WILL BE IN
THE MID 40S TO LOWER 50S.

STEADY WIDESPREAD PRECIPITATION WILL RETURN TONIGHT AND THURSDAY AS
A WARM FRONT MOVES INTO WESTERN WASHINGTON FROM THE SOUTHWEST. AN
ELONGATED NORTH-SOUTH COLD FRONT WILL MOVE INTO THE FORECAST AREA
THURSDAY NIGHT AND SLOWLY MOVE EAST ON FRIDAY. EVEN THOUGH MODELS
SHOW THIS SYSTEM SPLITTING SOMEWHAT -- ESPECIALLY THE COLD FRONT
-- THEY AGREE THAT PRECIPITATION WILL BE FAIRLY SIGNIFICANT. THE
850 MB FLOW WILL BE SOUTHWEST 40-50 KT TONIGHT AND THURSDAY BEFORE
GRADUALLY WEAKENING THURSDAY NIGHT...AND THE SNOW LEVEL WILL RISE
TO 6500 TO 7500 FT. SO PRECIPITATION TOTALS OF 3 TO 6 INCHES OVER
MUCH OF THE OLYMPICS AND AROUND MOUNT BAKER FOR WEDNESDAY NIGHT
THROUGH THURSDAY NIGHT LOOK REALISTIC.

THE SYSTEM WILL ALSO PRODUCE WINDY CONDITIONS IN THE NORTH
INTERIOR AND ALONG THE COAST...LOCALLY IN THE 20 TO 30 MPH RANGE
WITH GUSTS 40 MPH. THIS WOULD BE IN THE MARGINAL LOW END OF A
WIND ADVISORY...AND THERE HAS BEEN A SLIGHT TREND TOWARD WEAKER
SURFACE WINDS IN RECENT MODEL RUNS. SO WE WILL HOLD OFF ON ISSUING
AN ADVISORY AT THIS TIME.

AS MENTIONED ABOVE...THE COLD FRONT WILL MOVE EAST OF THE CASCADES
FRIDAY. SHOWERS WILL TAPER OFF FRIDAY AFTERNOON AND END MOST AREAS
FRIDAY NIGHT. THE SNOW LEVEL WILL FALL TO 4000 TO 5000 FT. MCDONNAL

.LONG TERM...AN UPPER TROUGH WILL BE CENTERED OVER THE NORTHERN
CALIFORNIA OFFSHORE WATERS FRIDAY NIGHT AND LIFT NORTHEAST ACROSS
THE PACIFIC NORTHWEST SATURDAY AND SATURDAY NIGHT. IT SHOULD BRING
SOME SHOWERS TO THE FORECAST AREA BUT NOTHING SIGNIFICANT. THE
SNOW LEVEL WILL BE 3000 TO 4000 FT. DRIER WEATHER IS LIKELY SUNDAY
AND MONDAY AS AN UPPER RIDGE PROGRESSES SLOWLY ACROSS THE REGION.
MODELS ARE IN FAIRLY GOOD AGREEMENT THAT ANOTHER FRONTAL SYSTEM
WILL BRING THE NEXT ROUND OF STEADY WIDESPREAD PRECIPITATION
MONDAY NIGHT AND TUESDAY...PROBABLY WITH SNOW LEVELS AGAIN
CLIMBING TO AROUND 6000 FT. MCDONNAL

&&

.AVIATION...NORTHWESTERLY FLOW ALOFT WILL TURN SOUTHWESTERLY
LATE THIS AFTERNOON AS A WEAK UPPER LEVEL RIDGE MOVES EAST ACROSS
THE AREA. AT THE SURFACE...WEAK HIGH PRESSURE OVER WESTERN
WASHINGTON THIS MORNING WILL BUILD AS IT MOVES EAST OF THE CASCADES
THIS AFTERNOON AND EVENING. A STRONG FRONTAL SYSTEM WILL MOVE INTO
THE COASTAL WATERS LATE TONIGHT. THE AIR MASS IS MOIST AND
STABLE...IT WILL DRY SOMEWHAT THIS AFTERNOON THEN BECOME
INCREASINGLY MOIST FROM THE WEST TONIGHT.

CONDITIONS ARE QUITE VARIABLE ACROSS THE AREA THIS MORNING WITH
MAINLY MVFR CEILINGS AND SOME IFR CEILINGS IN THE INTERIOR VALLEYS.
EXPECT THE LOWER LEVELS TO DRY OUT MIDDAY AS LOW LEVEL PRESSURE
GRADIENTS BECOMING INCREASINGLY OFFSHORE. PRECIPITATION WILL MOVE IN
FROM THE WEST THIS EVENING...BUT WITH EASTERLY PRES GRADIENTS EXPECT
CIGS AND VIS TO START OFF AS VFR THIS EVENING...THEN GRADUALLY
DETERIORATE ON THE OLYMPIC PENINSULA OVERNIGHT WHILE STAYING MAINLY
VFR IN THE INTERIOR.  ALBRECHT

KSEA...EXPECT P6SM WITH SCT-BKN010 AND LAYERS AT 050 AND ABOVE THIS
MORNING. CONDITIONS WILL BECOME GOOD VFR AROUND 20Z...THEN CIGS WILL
GRADUALLY FALL TO OVC035 LATE TONIGHT WITH -RA. WINDS WILL BE SOUTH
4-8 KT THIS MORNING AND WILL TURN TO THE EAST OR NORTHEAST 4-7 KT
AFTER ABOUT 20Z. ALBRECHT

&&

.MARINE...A WEAK RIDGE OF HIGH PRESSURE OVER WESTERN WASHINGTON
EARLY THIS MORNING WILL BUILD INTO EASTERN WASHINGTON THIS AFTERNOON
AND TONIGHT. IN THE MEAN TIME...A STRONG FRONTAL SYSTEM WRAPPING
AROUND A DEEP LOW NEAR 45N 145W SOUTHEAST TO ALONG 138W FROM 47N TO
40N THEN SOUTHWESTWARD WILL MOVE INTO THE COASTAL WATERS LATE
TONIGHT THEN ONLY CREEP EASTWARD TO THE WASHINGTON COASTLINE EARLY
THURSDAY EVENING. FULL GALES WILL SPREAD INTO THE COASTAL WATERS
TONIGHT. AN AREA OF GALES IN THE EASTERN PORTION OF THE CENTRAL
STRAIT OF JUAN DE FUCA AND THE EAST ENTRANCE IS ALSO EXPECTED TO
DEVELOP THIS EVENING AS FLOW ALOFT INTERACTS WITH THE OLYMPICS AND
RESULTS IN THE DEVELOPMENT OF A MESO LOW JUST EAST OF PORT ANGELES.
WINDS ARE EXPECTED TO REMAIN BELOW GALE STRENGTH IN THE OTHER WATERS
AS THE INCOMING FRONT WILL BE INCREASINGLY NORTH SOUTH ORIENTED AS
IT APPROACHES. WINDS WILL PEAK LATE TONIGHT AND EARLY THURSDAY
MORNING THEN WILL SLOWLY EASE THURSDAY AFTERNOON AS THE FRONT
WEAKENS AND MOVES EASTWARD INTO THE AREA.

GALE WARNINGS HAVE BEEN ISSUED FOR THE COASTAL WATERS AND THE
CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA. SMALL CRAFT ADVISORIES
ARE UP FOR THE REMAINING WATERS EXCEPT PUGET SOUND AND HOOD CANAL.

SEAS WILL BUILD TONIGHT AND THURSDAY...BUT THE HIGHEST SEAS ON THE
ORDER OF 17 TO 19 FEET FROM THE SOUTHWEST WILL REMAIN OVER THE OUTER
WATERS AND WILL BE RELATIVELY SHORT PERIOD IN NATURE - REDUCING THE
THREAT FOR SIGNIFICANT BEACH EROSION ON THE COASTLINE.

A WEAKER SYSTEM WILL MOVE THROUGH THE WATERS FRIDAY OR FRIDAY NIGHT.
A STRONGER SYSTEM WILL MOVE BY WELL TO THE SOUTH OF THE WATERS ON
SATURDAY. ALBRECHT

&&

.HYDROLOGY...ANOTHER 3 TO 6 INCHES OF PRECIPITATION WILL FALL OVER
THE OLYMPICS TONIGHT THROUGH THURSDAY NIGHT...WITH THE SNOW LEVEL
RISING TO 6500 TO 7500 FT. THIS WILL CAUSE THE SKOKOMISH RIVER --
WHICH ONLY FELL BELOW FLOOD STAGE TUESDAY MORNING -- TO FLOOD
AGAIN. IT WILL PROBABLY BEGIN THURSDAY MORNING...AND THE ONLY
REAL QUESTION IS WHETHER OR NOT IT WILL REACH ITS MAJOR FLOOD
STAGE. THE FLOOD WATCH WILL BE UPDATED EARLY THIS MORNING.

OTHER WESTERN WASHINGTON RIVERS FLOWING OFF THE OLYMPICS AND THE
NORTH CASCADES WILL ALSO RISE SIGNIFICANTLY. HOWEVER NORTHWEST
RIVER FORECAST CENTER GUIDANCE SHOWS MOST OF THESE RIVERS -- THE
SATSOP... ELWHA...DUNGENESS...SKAGIT...AND STILLAGUAMISH --
CRESTING AT MOST WITH AROUND 70 PERCENT OF THE DISCHARGE NEEDED TO
REACH FLOOD STAGE. SO THE THREAT ON THESE RIVERS LOOKS PRETTY LOW.
THE GUIDANCE FOR THE NOOKSACK SHOWS IT GETTING CLOSEST TO FLOOD
STAGE -- THE SOUTH FORK NOOKSACK SPECIFICALLY -- BUT STILL LESS
THAN 80 PERCENT OF THE DISCHARGE CORRESPONDING TO FLOOD STAGE.
AND IT IS WORTH NOTING THAT THE NOOKSACK DID NOT FLOOD DURING
EITHER OF THE WESTERN WASHINGTON FLOODING EPISODES IN NOVEMBER AND
DECEMBER. BOTTOM LINE IS I WILL UPDATE THE FLOOD POTENTIAL OUTLOOK
TO STATE THAT FLOODING IS UNLIKELY ON RIVERS OTHER THAN THE
SKOKOMISH.

OTHERWISE...RIVER FLOODING IS NOT EXPECTED THE NEXT 7 DAYS.
MCDONNAL

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WATCH FROM THIS EVENING THROUGH LATE FRIDAY NIGHT FOR HOOD
     CANAL AREA-LOWER CHEHALIS VALLEY AREA-OLYMPICS.

     WINTER WEATHER ADVISORY UNTIL 6 AM PST EARLY THIS MORNING FOR
     CASCADES OF PIERCE AND LEWIS COUNTIES.

PZ...SMALL CRAFT ADVISORY UNTIL 4 PM PST THIS AFTERNOON 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 4 PM THIS AFTERNOON TO 7 PM PST THURSDAY FOR
     CENTRAL U.S. WATERS STRAIT OF JUAN DE FUCA-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-EAST ENTRANCE U.S. WATERS STRAIT OF
     JUAN DE FUCA.

     SMALL CRAFT ADVISORY FOR ROUGH BAR UNTIL 7 PM PST THURSDAY FOR
     GRAYS HARBOR BAR.

     SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 7 PM PST THURSDAY
     FOR ADMIRALTY INLET-NORTHERN INLAND WATERS INCLUDING THE
     SAN JUAN ISLANDS.

     SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 7 PM PST
     THURSDAY FOR WEST ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA.

&&

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