Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 210411
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
910 PM PDT SUN APR 20 2014

.SYNOPSIS...HIGH PRESSURE WILL GIVE MAINLY DRY WEATHER TO THE AREA
TONIGHT. A STATIONARY FRONT JUST OFF THE COAST WILL BRING AN
INCREASING CHANCE OF SHOWERS TO WESTERN WASHINGTON THROUGH MONDAY AS
THE AIR BECOMES UNSTABLE. THE FRONT WILL MOVE INLAND MONDAY NIGHT.
ADDITIONAL WEATHER SYSTEMS WILL GIVE COOL AND UNSETTLED WEATHER
THROUGH NEXT WEEKEND.

&&

.SHORT TERM...A FRONT IS STALLED JUST OFF THE COAST THIS EVENING AND
THE RADARS SHOW RAIN JUST OFFSHORE. THE COMBINATION OF THE AIR
BECOME UNSTABLE MONDAY AND DIFFLUENT SSW FLOW ALOFT SHOULD ALLOW
SHOWERS TO INCREASE MONDAY...BECOMING MORE WIDESPREAD MONDAY NIGHT
AS THE FRONT AND ITS ASSOCIATED UPPER TROUGH FINALLY MOVE INLAND.
COOL ONSHORE FLOW AND THE UPPER TROUGH WILL GIVE A SHOWERY COOL DAY
ON TUESDAY. THE REST OF THE UPPER TROUGH WILL FOLLOW TUE NIGHT AND
WED FOR COOL WEATHER AND MORE SHOWERS. A WARM FRONT WILL APPROACH
THE AREA LATER WED. TEMPS ACROSS THE REGION THROUGH WED WILL BE A
FEW DEGREES BELOW NORMAL.

.LONG TERM...LARGE SCALE MODELS BRING A WETTER AND MORE ORGANIZED
FRONTAL SYSTEM ACROSS THE AREA WED NIGHT THROUGH THU OR THU NIGHT.
PER CONVERSATIONS WITH NESDIS...THIS SYSTEM...CURRENTLY NEAR THE
INTERNATIONAL DATELINE...HAS SOME TAP TO SUBTROPICAL MOISTURE FROM
THE WESTERN PACIFIC AND MAY RESULT IN SOME MODERATE PRECIPITATION
AMOUNTS. THIS HAS BEEN ADVERTISED BY ALL OF THE GLOBAL MODELS FOR
SEVERAL DAYS NOW. BEHIND THAT SYSTEM...MEAN UPPER TROUGHING OVER THE
EASTERN PACIFIC WILL MAINTAIN COOLER AND WETTER THAN AVERAGE
CONDITIONS FOR LATE APRIL. ALBRECHT

&&

.HYDROLOGY...RIVER FLOODING IS UNLIKELY FOR THE NEXT 7 DAYS.

THE EXCEPTION IS THE NORTH FORK OF THE STILLAGUAMISH RIVER EAST OF
THE SR 530 LANDSLIDE NEAR OSO WHERE A FLOOD WARNING REMAINS IN
EFFECT UNTIL FURTHER NOTICE. FLOODING CONTINUES FOR THIS RIVER AS A
RESULT OF WATER POOLED BEHIND THE DEBRIS DAM THAT PARTIALLY BLOCKS
THE RIVER.

AT 230 PM...THE NORTH FORK OF THE STILLAGUAMISH NEAR ARLINGTON IS
AT 5.5 FT...OR 4195 CFS. THE RIVER WILL RECEDE TO AROUND 4.5 FEET
LATE MONDAY AFTERNOON. THE NORTH FORK OF THE STILLAGUAMISH RIVER
NEAR OSO IS AT 217.0 FEET OR 2100 CFS. THE RIVER WILL RECEDE THROUGH
LATE MONDAY. THE SLIDE POOL EAST OF THE LANDSLIDE IS AT 284.2 FEET.
IT WILL ALSO SLOWLY RECEDE THROUGH MONDAY. ALBRECHT

&&

.AVIATION...HIGH PRESSURE ALOFT WILL SHIFT EWD TONIGHT AS A TROUGH
DEVELOPS OFFSHORE. THE TROUGH AND ASSOCIATED SURFACE FRONT WILL
SLOWLY PUSH INTO WRN WA MONDAY AND MONDAY NIGHT. MODERATE S/SW FLOW
ALOFT. STABLE ATMOSPHERE AND SOMEWHAT MOIST ALOFT BUT MAINLY DRY IN
THE LOW LEVELS. THE LOW LEVEL AIR MASS WILL GRADUALLY MOISTEN UP
THROUGH THE DAY MONDAY.

KSEA...CIGS EXPECTED TO REMAIN ABOVE 5K FT TONIGHT INTO MON. LIGHT
WIND...BECOMING NW 3-6 KT MONDAY AFTERNOON. DTM

&&

.MARINE...A COLD FRONT WILL DISSIPATE OVER THE WATERS THIS EVENING.
WINDS WILL REMAIN BELOW 20 KT THROUGHOUT. A SMALL CRAFT FOR
HAZARDOUS SEAS CONTINUES THROUGH MONDAY FOR THE COASTAL WATERS AND
WEST ENTRANCE TO THE STRAIT. WESTERLY SWELL AROUND 14 FEET OVER THE
COASTAL WATERS WILL SUBSIDE TO NEAR 12 FEET ON MONDAY. SWELL AT THE
WEST ENTRANCE AROUND 13 TO 14 FEET WILL SUBSIDE TO NEAR 10 FEET ON
MONDAY.

A HIGH SURF ADVISORY WILL EXPIRE AT 9 PM PDT. OBS INDICATE THAT
WAVES REACHING THE COAST HAVE FALLEN BELOW 15 FEET...BUT LARGE WAVES
ABOVE 10 FEET WILL CONTINUE THROUGH MONDAY. THEREFORE...THOSE
PLANNING ON BEACH ACTIVITIES SHOULD STILL BE ALERT FOR WAVES
SUDDENLY RACING FARTHER UP THE BEACH THAN NORMAL

&&

.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...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS COAST AND WEST STRAIT
     OF JUAN DE FUCA THROUGH MONDAY EVENING.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR THROUGH MONDAY
     MORNING.

&&

$$

WWW.WEATHER.GOV/SEATTLE

FOR THE GRAPHICAL AFD...VISIT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML





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