River Flood Warning 50, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
406 AM PST FRI NOV 13 2015

.SYNOPSIS...A STRONG FRONTAL SYSTEM WILL BRING VERY WET WEATHER TO
WESTERN WASHINGTON THROUGH SATURDAY NIGHT. AN UPPER LEVEL TROUGH
WILL BRING SHOWERS AND COOLER WEATHER TO THE AREA SUNDAY AFTERNOON
AND NIGHT. RAIN WILL RESUME ON MONDAY AS WARM FRONT REACHES THE
REGION...FOLLOWED BY A COLD FRONT ON WEDNESDAY.

&&

.SHORT TERM...AN ATMOSPHERIC RIVER...I.E. MOIST AND STRONG W FLOW
ALOFT WILL CONTINUE TO BRING COPIOUS RAIN TO W WA TODAY. RAIN RATES
WILL BEGIN DIMINISHING LATE THIS AFTERNOON OR THIS EVENING AS THE
STRONG WARM ADVECTION WEAKENS. AN APPROACHING UPPER LEVEL SHORTWAVE
TROUGH WILL CAUSE A WAVE TO DEVELOP ON THE ATMOSPHERIC RIVER
TONIGHT. THIS WILL SHIFT THE FLOW ALOFT OVER W WA TO A SW DIRECTION
AND SHIFT THE HEAVIEST RAIN OVER SW WA AND THE CENTRAL CASCADES. THE
SOUTHWARD SHIFT ALSO ALLOWS COOLER AIR TO MOVE OVER THE N PART OF W
WA ALLOWING SNOW LEVELS TO LOWER BELOW 5000 FEET AT HURRICANE RIDGE
AND MOUNT BAKER. HEAVY RAIN WILL CONTINUE AT TIMES ON SATURDAY BUT
WITH SOMEWHAT LOWER RAIN RATES. THE MAIN RAIN AREA WILL CONTINUE
SHIFTING AROUND THROUGH SATURDAY NIGHT AS THE UPPER LEVEL TROUGH
NEARS THE AREA. THE UPPER LEVEL TROUGH WILL MOVE ACROSS THE AREA ON
SUNDAY WITH RAIN CHANGING TO SCATTERED SHOWERS. COOLER AIR WITH THE
TROUGH WILL LOWER SNOW LEVELS FROM 7000 FEET OR HIGHER TODAY....DOWN
TO 2000-3000 FEET ON SUNDAY.

SNOW LEVELS HAVE RISEN TO AROUND 7000 FEET THIS MORNING WITH SNOW
FINALLY CHANGING TO RAIN AT MOUNT BAKER. THE WINTER WEATHER ADVISORY
HAS ENDED. HOWEVER AS MENTIONED ABOVE...COOLER AIR ALOFT WILL LOWER
THE SNOW LEVEL BACK BELOW 5000 FEET ON SATURDAY...WITH SNOW
RESUMING. IF PRECIP RATES REMAIN HIGH ENOUGH ANOTHER 2-7 INCHES OR
SO OF SNOW MAY ACCUMULATE AT BAKER AND HURRICANE RIDGE ON SATURDAY.
CONFIDENCE IS ONLY MARGINAL AT THIS POINT SINCE SO MUCH DEPENDS UPON
THE PRECIP RATE. SNOW WILL CONTINUE OVER THE NORTH PART SATURDAY
NIGHT SO THERE COULD BE ENOUGH PRECIP FOR ANOTHER 5-10 INCHES. SNOW
LEVELS WILL PROBABLY STILL BE TOO HIGH FOR SNOW TO REACH THE LOWER
CENTRAL CASCADE PASSES.

FAIRLY STRONG SURFACE PRESSURE GRADIENTS CONTINUE OVER W WA THIS
MORNING...BUT WINDS OVER THE MAJORITY OF THE AREA HAVE EASED BELOW
ADVISORY CRITERIA. HOWEVER WITH SOME SPOTS STILL GETTING WINDS CLOSE
TO 30G40 MPH THE WIND ADVISORY WILL CONTINUE THROUGH 18Z/10 AM.
PRESSURE GRADIENTS WILL SLOWLY WEAKENING THIS MORNING AND AFTERNOON
SO WINDS SHOULD BE BELOW CRITERIA EVERYWHERE EXCEPT THE CENTRAL
COAST BY LATE THIS MORNING.

A SURFACE LOW ASSOCIATED WITH THE APPROACHING UPPER LEVEL TROUGH AND
WAVE ON THE FRONT WILL REACH THE AREA SATURDAY NIGHT. THE NAM TRACKS
THE SURFACE LOW ACROSS OREGON...BUT THE GFS BRINGS IT ACROSS SW WA.
THERE IS SOME POTENTIAL FOR ANOTHER PERIOD OF WINDY CONDITIONS LATE
SATURDAY NIGHT IF THE GFS IS CORRECT. HOWEVER CONFIDENCE IS NOT VERY
HIGH AT THIS POINT. KAM

.LONG TERM...THE UPPER LEVEL TROUGH WILL MOVE E OF W WA SUNDAY NIGHT
BUT A SOMEWHAT UNSTABLE SHOWERY AIR MASS WILL CONTINUE OVER W WA
WITH SNOW LEVELS DOWN AROUND 2000 FEET. THE GFS AND ECMWF HAVE BEEN
HAVING CONSISTENCY PROBLEMS FOR EARLY NEXT WEEK...BUT SEEM TO HAVE
SETTLED ON A WARM FRONT REACHING THE AREA MONDAY AFTERNOON AND
MONDAY NIGHT. BOTH MODELS BRING THE TRAILING COLD FRONT ACROSS THE
AREA...BUT DIFFER ON THE TIMING. THE ECMWF BRINGS IT ACROSS THE AREA
TUESDAY NIGHT WHILE THE GFS HOLDS OFF UNTIL WEDNESDAY NIGHT. KAM

&&

.HYDROLOGY...HEAVY RAIN WILL CONTINUE IN THE MOUNTAINS TODAY WITH
THE HEAVIEST AMOUNTS IN THE OLYMPICS AND NORTH CASCADES. THANKS TO
THE OLYMPEX PROJECT THERE ARE PLENTY OF RAIN GAUGES AROUND THE
OLYMPICS. SOME OF THE 00Z-09Z RAINFALL TOTALS ARE QUITE IMPRESSIVE
WITH A CORE OF 4 TO 6 INCHES IN THE THREE GAUGES NEAR LAKE QUINAULT.
OTHER GAUGES ALONG THE SOUTH SLOPES OF THE OLYMPICS REPORTING 2.5 TO
3.5 INCHES. RAINFALL AMOUNTS ARE A LITTLE LOWER ALONG THE WEST
SLOPES WITH 2 TO NEAR 3 INCHES. THESE HIGH RAINFALL RATES WILL
CONTINUE THROUGH 18Z THEN SLOWLY TAPER OFF THIS AFTERNOON AND
DRASTICALLY SLOW DOWN LATE THIS AFTERNOON INTO THIS EVENING.

FOR THE CASCADES RAINFALL AMOUNTS OVERNIGHT HAVE GENERALLY BEEN IN
THE 1 TO 2 INCH RANGE WITH THE HIGHEST AMOUNTS IN THE CENTRAL
CASCADES NEAR SKYKOMISH. HIGH RAINFALL RATES WILL CONTINUE IN THE
NORTHERN AND CENTRAL CASCADES TODAY THEN EASE TONIGHT INTO SATURDAY
MORNING.

FLOOD WARNINGS HAVE ALREADY BEEN ISSUED FOR THE SKOKOMISH AND
BOGACHIEL RIVERS. OTHER OLYMPIC PENINSULA RIVERS ARE RISING RAPIDLY
AND THE NEXT FORECAST UPDATE WILL LIKELY INCLUDE FLOOD WARNINGS ON
AT SOME OF THESE RIVERS. IN THE CASCADES ANY RIVER FROM THE NOOKSACK
IN THE NORTH TO THE COWLITZ IN THE SOUTH COULD FLOOD. A FLOOD WATCH
REMAINS IN EFFECT FOR ALL COUNTIES THAT HAVE MAIN STEM RIVERS. FELTON

&&

.AVIATION...A STRONG FRONTAL SYSTEM OVER THE AREA WILL SAG SOUTH
LATER TODAY AND TONIGHT WITH WESTERLY FLOW ALOFT. AIR MASS MOIST AND
STABLE.

KSEA...LOW CLOUDS AND OCCASIONAL REDUCED VISIBILITIES WILL PREVAIL
TODAY AND TONIGHT. SOUTHERLY WIND 15 TO 25 KNOTS...EASING TO 5 TO
10 KNOTS TONIGHT. SCHNEIDER

&&

.MARINE...GALE FORCE WINDS OVER THE WATERS WILL EASE TODAY
AS A STRONG FRONTAL SYSTEM SAGS SOUTH. LONG PERIOD WEST SWELL
18-22 FEET WILL AFFECT THE COASTAL WATERS TODAY...THEN SUBSIDE ON
SATURDAY.

A COLD FRONT WILL STALL OVER THE REGION ON SATURDAY. MODERATE
ONSHORE FLOW WILL PREVAIL ON SUNDAY. ANOTHER VIGOROUS FRONTAL SYSTEM
WILL IMPACT THE WATERS MONDAY AND MONDAY NIGHT. SCHNEIDER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WIND ADVISORY CENTRAL COAST UNTIL 4 PM THIS AFTERNOON.
     WIND ADVISORY INTERIOR LOWLANDS AND NORTH COAST UNTIL
      10 AM THIS MORNING.
     HIGH SURF ADVISORY IN EFFECT UNTIL NOON PST SATURDAY
     FOR THE COAST.
	 FLOOD WATCHES AND/OR FLOOD WARNINGS ARE IN EFFECT FOR
	 THE CWA.

PZ...GALE WARNINGS UNTIL 1 PM FOR THE COAST...ENTRANCES TO THE
      STRAIT...ADMIRALTY INLET AND THE NORTH INLAND WATERS.
     GALE WARNING UNTIL 5 PM PST THIS AFTERNOON FOR PUGET SOUND.
     SMALL CRAFT ADVISORY UNTIL 11 PM PST THIS EVENING FOR
      THE CENTRAL STRAIT.
     SMALL CRAFT ADVISORY FOR ROUGH BAR UNTIL 4 PM PST THIS AFTERNOON
      FOR GRAYS HARBOR BAR.

&&

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