Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 140950
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 AM PDT MON APR 14 2014

.SYNOPSIS...A STRONG UPPER LEVEL RIDGE AND OFFSHORE LOW LEVEL FLOW
WILL KEEP WESTERN WASHINGTON DRY TODAY. STRONG ONSHORE FLOW WILL
DEVELOP THIS AFTERNOON AND CLOUDS WILL SPREAD INLAND THIS EVENING AS
THE UPPER RIDGE SHIFTS EAST AND A FRONTAL SYSTEM PUSHES THROUGH THE
AREA. A SERIES OF WEATHER SYSTEMS WILL MOVE ACROSS THE AREA TUESDAY
THROUGH THE REMAINDER OF THE WEEK BRINGING MOSTLY CLOUDY CONDITIONS
WITH A CHANCE OF SHOWERS.

&&

.SHORT TERM...A STRONG UPPER LEVEL RIDGE OVER THE COASTAL WATERS
WILL SHIFT INLAND LATER THIS MORNING AND EAST OF THE CASCADES THIS
AFTERNOON THROUGH TONIGHT. OFFSHORE FLOW WILL DIMINISH AS THE UPPER
RIDGE MOVES BY...AND STRONG ONSHORE FLOW WILL DEVELOP ACROSS THE
REGION BY LATE THIS AFTERNOON. THE ONSHORE FLOW IS INCREASING IN
RESPONSE TO A SHORT WAVE UPPER TROUGH THAT IS MOVING INTO HAIDA
GWAII LATE THIS AFTERNOON. SKIES ACROSS THE REGION ARE CLEAR EARLY
THIS MORNING...BUT AN AREA OF CLOUDS CAN BE SEEN MARCHING EASTWARD
INTO THE COASTAL WATERS THIS MORNING. EXPECT THESE CLOUDS TO SPREAD
ONSHORE MIDDAY AND INTO THE INTERIOR AROUND OR SHORTLY AFTER THE
EVENING COMMUTE TIME.

SHOWER CHANCES WILL INCREASE RAPIDLY IN THE MOUNTAINS THIS EVENING
AS THE INCREASING WESTERLY FLOW GETS LIFTED BY THE TERRAIN AND THE
UPPER TROUGH. MOISTURE INCREASES TO BETWEEN 3000 AND 10000 FEET
LATER TONIGHT ACROSS THE AREA FOR A CHANCE OF SHOWERS. SHOWERS WILL
BE LIKELY OVER THE MOUNTAINS AND AROUND A PUGET SOUND CONVERGENCE
ZONE THAT SHOULD FROM BETWEEN EVERETT AND SEATTLE.

MOIST WNW FLOW ALOFT...ONSHORE FLOW...AND PASSING MID LEVEL
DISTURBANCES WILL KEEP THE CHANCE OF SHOWERS GOING TUE INTO TUE
EVENING.

MODEL DIFFERENCES SHOW UP STARTING WED. THE GFS AND NAM SOLUTIONS
SHOW MORE AMPLITUDE IN THE FLOW WITH A MORE SIGNIFICANT LOOKING
UPPER RIDGE PASSING ACROSS THE AREA. THE CANADIAN AND ECMWF ARE
FLATTER AND SHOW SOME WARM ADVECTION PRECIPITATION WED INTO WED
EVENING. THE STRONG JET SEEN ALONG 40N N OF HAWAII WOULD SUPPORT THE
FLATTER/WETTER SOLUTION...BUT FOR NOW THE FORECAST CURRENTLY SPLITS
THE DIFFERENCE BETWEEN THE TWO SOLUTIONS AND WILL BE MAINTAINED.
MAYBE THE 12Z SOLUTIONS WILL START CONVERGING. ALBRECHT

.LONG TERM...THE GFS/CANADIAN/ECMWF SOLUTIONS ALL GENERALLY AGREE
THAT A RATHER WET LOOKING COLD FRONT WILL MOVE ACROSS THE AREA LATE
THURSDAY INTO THURSDAY NIGHT. LIKELY POPS ARE INDICATED FOR THIS
SYSTEM. THEN FOR FRI THROUGH NEXT WEEKEND...MODELS GENERALLY SHOW
LOW AMPLITUDE RIDGING ON THE WEST COAST WITH SYSTEMS MOVING ENE AND
CLIPPING AT LEAST THE COASTAL AREAS AT TIMES. SOME SHOW SYSTEMS
REMAINING FARTHER OFFSHORE WHILE OTHERS DRIVE SYSTEMS INLAND. THE
CURRENT BROAD BRUSH FORECAST WILL BE MAINTAINED. ALBRECHT

&&

.HYDROLOGY...RIVER FLOODING IS UNLIKELY ON AREA RIVERS...EXCEPT THE
NORTH FORK OF THE STILLAGUAMISH EAST OF THE SR 530 LANDSLIDE NEAR
OSO...FOR THE NEXT 7 DAYS.

A FLOOD WARNING REMAINS IN EFFECT UNTIL FURTHER NOTICE FOR THE
NORTH FORK OF THE STILLAGUAMISH RIVER IN SNOHOMISH COUNTY JUST
UPSTREAM OF THE SR 530 LANDSLIDE. FLOODING CONTINUES AS A RESULT
OF WATER POOLED BEHIND THE DEBRIS DAM THAT PARTIALLY BLOCKS THE
RIVER.

THE NORTH FORK STILLAGUAMISH NEAR ARLINGTON AND THE POOL UPSTREAM OF
THE SR 530 SLIDE WILL VERY SLOWLY FALL THROUGH TODAY AS DRY WEATHER
CONTINUES. THE RIVER AND UPSTREAM POOL ARE FORECAST TO RISE ABOUT A
FOOT TUESDAY AFTERNOON AND EVENING...THEN RESUME A SLOW DOWNWARD
TREND.  AT THIS TIME...THE MOST SIGNIFICANT SYSTEMS ARE EXPECTED
LATE MONDAY NIGHT THROUGH TUESDAY MORNING...GIVING AROUND A HALF
INCH OF RAIN TO THE SLIDE AREA...AND ON THURSDAY NIGHT...GIVING
ANOTHER QUARTER TO HALF AN INCH OF RAIN TO THE SLIDE AREA. LIGHT
SHOWERS AT OTHER TIMES WILL NOT GIVE HYDROLOGICALLY SIGNIFICANT
RAINFALL TO THE SLIDE AREA...BUT WILL KEEP CONDITIONS WET. ALBRECHT

&&

.AVIATION...HIGH PRESSURE WILL MOVE E ALLOWING A LOW PRESSURE TROUGH
TO MOVE OVER THE REGION. LIGHT TO MODERATE SW FLOW ALOFT. DRY AND
STABLE THIS MORNING...THEN INCREASING LOW AND MID LEVEL MOISTURE
ALONG THE COAST SPREADING INLAND TONIGHT.

KSEA...LIGHT AND VARIABLE WIND BECOMING LIGHT SLY WIND THIS
MORNING...INCREASING LATER TODAY AND THIS EVENING AS A FRONT PASSES
THE AREA.

&&

.MARINE...ONSHORE FLOW WILL DEVELOP ALONG THE COAST THIS MORNING AND
ACROSS THE INLAND WATERS THIS AFTERNOON BEHIND A FRONT. WLY GALES
WILL LIKELY DEVELOP IN THE CENTRAL/E STRAIT THIS AFTERNOON AND
PERSIST THROUGH THIS EVENING. ONSHORE/WLY FLOW TUESDAY WILL BECOME
LIGHTER ON WED. A WEAKER FRONT MAY AFFECT THE WATERS LATE IN THE
WEEK.


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WARNING REMAINS IN EFFECT FOR THE NORTH FORK OF THE
      STILLAGUAMISH RIVER EAST OF THE SR 530 LANDSLIDE.

PZ...GALE WARNING THIS AFTERNOON THROUGH LATE TONIGHT FOR
      THE CENTRAL AND EAST STRAIT OF JUAN DE FUCA.
     SMALL CRAFT ADVISORY FROM 11 AM PDT THIS MORNING THROUGH THIS
      EVENING FOR THE OUTER COASTAL WATERS.
     SMALL CRAFT ADVISORY IN EFFECT THIS AFTERNOON THROUGH THIS
      EVENING FOR THE WESTERN STRAIT OF JUAN DE FUCA.

&&

$$

WWW.WEATHER.GOV/SEATTLE

YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT
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