Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 181601
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT FRI OCT 17 2014

.SYNOPSIS...CLOUDS WILL LINGER THIS MORNING BUT SUN BREAKS ARE
POSSIBLE IN THE AFTERNOON AS AN UPPER RIDGE BUILDS. THE RIDGE WILL
GIVE DRY AND WARMER WEATHER SUNDAY OVER THE INTERIOR AHEAD OF THE
NEXT SYSTEM. A FRONT WILL BRING RAIN TO THE COAST LATE SUNDAY...AND
TO THE INTERIOR SUNDAY NIGHT AND MONDAY. A SERIES OF FRONTAL SYSTEMS
WILL MAINTAIN A WET PATTERN THE REST OF NEXT WEEK.

&&

.SHORT TERM...ANY SHOWERS SEEM ISOLATED NOW THOUGH THERE COULD STILL
BE SOME OVER THE MOUNTAINS. SATELLITE IMAGERY SHOWS A BIG HOLE IN
THE CLOUDS OVER THE EAST ENTRANCE AND ADJACENT MARINE AREAS. SUN
BREAKS SEEM PRETTY LIKELY IN THE AFTERNOON. HIGHS TODAY WILL BE IN
THE LOWER TO MID 60S.

SUNDAY WILL BE A FEW DEGREES WARMER WITH SOME LOW 70S POSSIBLE OVER
THE INTERIOR. THERE WILL PROBABLY BE MORE SUN WITH ONLY HIGH CLOUDS
IN THE AFTERNOON. RAIN JUST TOUCHES THE COAST IN THE AFTERNOON THEN
SPREADS INLAND SUNDAY NIGHT. MONDAY WILL BE RAINY IN THE MORNING AND
SHOWERY IN THE AFTERNOON WITH HIGHS IN THE 60S. BURKE

.LONG TERM...PREVIOUS DISCUSSION...GLOBAL MODELS SHOW A MORE
CONSOLIDATED FLOW PATTERN OVER THE ERN PAC TO STEER STRONGER SYSTEMS
INTO THE PAC NW THROUGH THE REST OF THE WEEK. TUESDAY WILL FEATURE A
RELATIVE BREAK IN STEADY RAINFALL BETWEEN SYSTEMS. RAIN ALONG THE
COAST AND MOUNTAINS IS LIKELY BUT ONLY A CHANCE INLAND. A STRONGER
TROUGH ACCOMPANIED BY A 150+ KT JET WILL DIRECT MOISTURE UNDER SWLY
FLOW INTO THE PAC NW  BY TUESDAY NIGHT. THE LATEST 00Z GFS/ECMWF
RUNS STILL DEPICT MORE SUBSTANTIAL RAINFALL AMOUNTS ACROSS THE AREA
WEDNESDAY AND THURSDAY. NEWER MODELS HAVE TRENDED MORE PROGRESSIVE
WITH EMBEDDED WAVES WHICH WOULD SHIFT THE MOISTURE STREAM AND LIMIT
THE FLOOD POTENTIAL ACROSS THE AREA. PREVIOUS MODELS YESTERDAY WHERE
SHOWING A MORE PERSISTENT ATMOSPHERIC RIVER EVENT. THIS PATTERN
STILL WARRANTS A CLOSE EYE AS TROPICAL MOISTURE FLOW NEAR HAWAII MAY
BECOME ENTRAINED INTO THE FLOW.

MODELS GENERALLY AGREE THAT HIGH PRESSURE WILL BUILD OVER THE
INTERIOR W WITH A TROUGH OUT ALONG 140 W BY FRIDAY. THIS SHOULD CUT
OFF THE MOISTURE FEED...AT LEAST TEMPORARILY. SHOWERS ARE STILL
INDICATED IN THE FORECAST BUT HEAVIER RAIN...IF IT OCCURS...SHOULD
ABATE. MERCER

&&

.HYDROLOGY...PREVIOUS DISCUSSION...THE SYSTEM ARRIVING MONDAY WILL
LIKELY BRING LESS THAN ONE INCH OF RAIN TO THE MOUNTAINS. THIS WOULD
NOT BE ENOUGH TO FLOOD AREA RIVERS INCLUDING THE SKOKOMISH. A LULL
IN PRECIPITATION ON TUESDAY WILL ALLOW RISES ON AREA RIVERS TO
RECEDE.

MORE SIGNIFICANT RAIN AMOUNTS ARE EXPECTED WEDNESDAY AND THURSDAY.
TROPICAL MOISTURE MAY BECOME ENTRAINED IN THE SWLY FLOW PATTERN.
HOWEVER...LATEST MODELS SHOW EMBEDDED WAVES TO CAUSE SOME SHIFTING
OF THE ATMOSPHERIC RIVER. THIS WILL DISPERSE RAIN OVER A LARGER AREA
AND IF UNFOLDS AS THE 00Z GFS SHOWS...SHOULD RESULT IN ONLY MINOR
FLOODING IF ANY. THE EXCEPTION MIGHT BE THE SKOKOMISH RIVER WHERE
STRONG SWLY FLOW CAN EASILY LEAD TO FLOODING. THIS EVENT IS FAR
ENOUGH OUT IN TIME SO THAT A HIGH DEGREE OF UNCERTAINTY EXISTS. MORE
WIDESPREAD FLOODING CANNOT BE RULED OUT AND THE FORECAST SHOULD BE
CLOSELY MONITORED. SOME RELIEF IN RAINFALL APPEARS LIKELY BY FRIDAY
AS THE FLOW LIFTS NWD WITH HIGH PRESSURE STRENGTHENING OVER THE
INTERIOR.  MERCER

&&

.AVIATION...WESTERLY FLOW ALOFT...BECOMING MORE SOUTHERLY TONIGHT.
AT THE SURFACE...WEAK HIGH PRESSURE WILL BE OVER WESTERN WASHINGTON
TODAY...THEN INCREASING EASTERLY GRADIENTS TONIGHT AS A FRONT
APPROACHES FROM THE WEST. AIR MASS MOIST AND STABLE...WITH SOME
DRYING IN THE LOW LEVELS THIS AFTERNOON AND EVENING.

KSEA...LOW CLOUDS SHOULD LIFT AND BREAK UP THIS AFTERNOON. SOUTHERLY
WINDS 4 TO 8 KNOTS. SCHNEIDER

&&

.MARINE...HIGH PRESSURE WILL BE OVER THE AREA TODAY. SOUTHEASTERLY
GRADIENTS WILL INCREASE TODAY AS A FRONT APPROACHES FROM THE WEST.
THIS WILL BRING SMALL CRAFT ADVISORY WINDS TO THE COASTAL WATERS
TODAY...AND THEN TO MOST OF THE INLAND WATERS TONIGHT. THE FRONT
WILL MOVE THROUGH THE WATERS SUNDAY AND MONDAY WITH GALES POSSIBLE
OVER THE COASTAL WATERS SUNDAY AND SMALL CRAFT ADVISORY WINDS ALL
OTHER WATERS. A SECOND FAIRLY VIGOROUS FRONTAL SYSTEM WILL MOVE
THROUGH THE WATERS TUESDAY AND TUESDAY NIGHT. SCHNEIDER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY COASTAL WATERS AND WEST ENTRANCE STRAIT OF
     JUAN DE FUCA.
    .GALE WATCH COASTAL WATERS SUNDAY.

&&

$$

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YOU CAN SEE AN ILLUSTRATED VERSION OF THIS FORECAST DISCUSSION AT
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