Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 211035
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
335 AM PDT MON APR 21 2014

.SYNOPSIS...A STATIONARY FRONT JUST OFF THE COAST WILL BRING RAIN TO
THE NORTH COAST TODAY WITH A CHANCE OF SHOWERS ELSEWHERE. THE FRONT
WILL MOVE INLAND TONIGHT. A COOL AND WET PATTERN FOR APRIL WILL SET
UP FOR THE REMAINDER OF THE WEEK INTO THE WEEKEND WITH MORE WEATHER
SYSTEMS MOVING THROUGH THE AREA.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS CLOUDY SKIES OVER WESTERN
WASHINGTON AT 3 AM. STATIONARY FRONT OFFSHORE EXTENDING FROM ABOUT
30 MILES WEST OF CAPE FLATTERY TO ABOUT 100 NM WEST OF HOQUIAM. RAIN
STARTED AT KUIL AROUND 0530Z/1030 PM LAST NIGHT. ABOUT A THIRD OF AN
INCH OF RAIN HAS FALLEN AT KUIL SINCE THE RAIN STARTED. TEMPERATURES
AT 3 AM WERE IN THE 40S.

NOT MUCH CHANGE TO THE FORECAST THIS MORNING WITH A COOL AND WET FOR
APRIL SPELL OF WEATHER THIS WEEK. DIGGING TROUGH OFFSHORE BETWEEN
130-140W COMBINED WITH AN AMPLIFYING RIDGE OVER MONTANA WILL KEEP
THE FRONT OFFSHORE FROM MAKING MUCH EASTWARD PROGRESS TODAY. RAIN
WILL CONTINUE ALONG THE NORTH COAST. FOR THE REMAINDER OF THE AREA
WHILE THE DIFFLUENT SOUTH SOUTHWESTERLY FLOW ALOFT IS STILL IN PLACE
THE THICKNESS OF THE CLOUD COVER WILL HINDER THE AIR MASS FROM
BECOMING UNSTABLE LATER THIS MORNING INTO THIS AFTERNOON. HAVE CUT
BACK THE POPS AND TAKEN THE SHOWER CHANCES OUT OF THE INTERIOR
LOWLANDS THIS MORNING. WITH ALL OF THE CLOUD COVER TEMPERATURES WILL
HAVE A HARD TIME GETTING OUT OF THE 50S.

UPPER LEVEL TROUGH OFFSHORE AND UPPER LEVEL RIDGE TO THE EAST MOVING
EASTWARD TONIGHT. THIS WILL ALLOW WHAT IS LEFT OF THE FRONT TO MOVE
INLAND OVERNIGHT WITH THE UPPER LEVEL TROUGH FOLLOWING RIGHT BEHIND
THE FRONT. WITH THE FRONT ALMOST PARALLEL TO THE FLOW ALOFT THE
EASTWARD MOVEMENT WILL BE SLOW WITH SHOWERS CONTINUING INTO THE
EARLY MORNING HOURS ON TUESDAY. PLENTY OF CLOUD COVER WILL KEEP LOWS
IN THE 40S.

UPPER LEVEL TROUGH STILL OVER THE AREA TUESDAY MORNING. IN ADDITION
CONVERGENCE PATTERN SETTING UP OVER THE CENTRAL SOUND ENHANCING THE
SHOWER ACTIVITY. TROUGH AXIS MOVING INTO THE CASCADES LATE IN THE
DAY WITH THE SHOWER ACTIVITY DECREASING AS THE DAY WEARS ON.
TEMPERATURES ALOFT COOLING MONDAY NIGHT INTO TUESDAY WITH THE 850 MB
TEMPERATURES NEAR OR JUST BELOW 0C. WITH PLENTY OF CLOUD COVER AND A
COOL AIR MASS OVERHEAD HIGHS ON TUESDAY WILL BE A FEW DEGREES BELOW
NORMAL...LOWER TO MID 50S.

SLIGHT BREAK IN THE WEATHER TUESDAY NIGHT BUT WITH SOME TROUGHINESS
STILL OVER THE AREA WILL HAVE TO KEEP A CHANCE OF SHOWERS IN THE
FORECAST.

MODELS SOLUTIONS FOR WEDNESDAY ARE A LITTLE MORE CONSISTENT ON THE
00Z RUN BUT STILL HAVE SOME DIFFERENCES. THE GFS BUILDS A WEAK UPPER
LEVEL RIDGE OFF THE COAST WHICH TURNS THE FLOW ALOFT WEST
NORTHWESTERLY PUSHING THE NEXT SHORTWAVE MOSTLY INTO WESTERN OREGON
AND SOUTHWESTERN WASHINGTON ON WEDNESDAY. THE ECMWF DOESN`T BUILD
THE RIDGE OFF THE COAST KEEPING THE FLOW ALOFT WESTERLY MOVING THE
NEXT SHORTWAVE INTO WESTERN WASHINGTON. THE GFS HAS BEEN
SLOWLY TRENDING NORTHWARD WITH THIS FEATURE IN THE LAST FEW RUNS.
WILL GO WITH CATEGORICAL POPS FOR THE SOUTHERN PORTION OF THE
CWA...LIKELY IN THE CENTRAL...AND CHANCE POPS IN THE NORTH.
TEMPERATURES ALOFT NOT WARMING UP MUCH WITH THE 850 MB TEMPERATURES
JUST ABOVE 0. THIS WILL KEEP HIGHS IN THE 50S.

.LONG TERM...00Z EXTENDED MODELS ARE CONSISTENT IN BRINGING A WETTER
AND MORE ORGANIZED FRONTAL SYSTEM ACROSS THE AREA WEDNESDAY NIGHT
THROUGH THURSDAY. THIS SYSTEM...CURRENTLY NEAR 170W...HAS SOME TAP
TO SUBTROPICAL MOISTURE FROM THE WESTERN PACIFIC AND MAY RESULT IN
SOME MODERATE PRECIPITATION AMOUNTS. BEHIND THE FRONT...COOL UPPER
LEVEL TROUGH SETTING UP OVER THE PACIFIC NORTHWEST FOR THURSDAY
NIGHT INTO SATURDAY. ONCE AGAIN THE GFS IS A LITTLE DEEPER WITH THE
TROUGH PULLING MORE OF THE SHOWER ACTIVITY TO THE SOUTH OF THE AREA
FRIDAY AND FRIDAY NIGHT VERSUS THE ECMWF. THE CANADIAN WHICH WAS
MORE IN LINE WITH THE ECMWF IS NOW LOOKING MORE LIKE THE GFS. AT
THIS POINT WITH THE LACK OF CONSISTENCY WILL HAVE TO KEEP A CHANCE
OF SHOWERS IN THE FORECAST FOR FRIDAY AND SATURDAY. BETTER AGREEMENT
IN THE MODELS ON SUNDAY WITH ANOTHER ORGANIZED SYSTEM MOVING INTO
THE AREA. TEMPERATURES WILL REMAIN BELOW NORMAL FOR THIS TIME OF
YEAR WITH HIGHS STAYING IN THE 50S. FELTON

&&

.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 215 AM...THE NORTH FORK OF THE STILLAGUAMISH NEAR ARLINGTON IS AT
4.9 FT...OR 3250 CFS. THE RIVER WILL RECEDE TO AROUND 4.5 FEET BY
LATE THIS AFTERNOON THEN REMAIN STEADY THROUGH THE EVENING HOURS.
THE RIVER WILL RISE AGAIN ON TUESDAY CRESTING NEAR 5.8 FEET/4700 CFS
TUESDAY NIGHT. THE NORTH FORK OF THE STILLAGUAMISH RIVER NEAR OSO IS
AT 216.6 FEET OR 2030 CFS. THE RIVER WILL RECEDE THROUGH LATE TODAY.
THE SLIDE POOL EAST OF THE LANDSLIDE IS AT 283.7 FEET. IT WILL ALSO
SLOWLY RECEDE TODAY. FELTON

&&

.AVIATION...AN UPPER LEVEL TROUGH AND ASSOCIATED FRONT JUST OFFSHORE
WILL SLOWLY PUSH INTO WRN WA LATE TODAY AND TONIGHT. MODERATE S/SW
FLOW ALOFT. STABLE ATMOSPHERE WITH HIGH LEVEL MOISTURE...BECOMING
WEAKLY UNSTABLE AND MOIST AT ALL LEVELS LATE THIS AFTERNOON AND
EVENING. SHOWERS INCREASING LATE THIS AFTERNOON/EVENING. VFR
CONDITIONS THROUGH TONIGHT.

KSEA...CIGS EXPECTED TO REMAIN ABOVE 5K FT THROUGH TONIGHT. LIGHT
WIND...BECOMING NW 3-6 KT THIS AFTERNOON. SHOWERS DEVELOPING AFTER
00Z.

&&

.MARINE...A SMALL CRAFT FOR HAZARDOUS SEAS CONTINUES THROUGH TODAY
FOR THE COASTAL WATERS AND WEST ENTRANCE TO THE STRAIT. WESTERLY
SWELL AROUND 12 TO 14 FEET OVER THE COASTAL WATERS WILL SUBSIDE TO
10 FEET BY THIS EVENING. SWELL OF 11 TO 13 FEET AT THE W ENTRANCE
WILL SUBSIDE BELOW 10 FT BY THIS EVENING.

PRESSURE GRADIENTS ARE GENERALLY LIGHT TODAY. STRONGER ONSHORE FLOW
DEVELOPS THIS EVENING WITH SMALL CRAFT WINDS POSSIBLE IN THE
CENTRAL/E STRAIT.

&&

.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 THIS AFTERNOON.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR THROUGH THIS
     AFTERNOON.

&&

$$

WWW.WEATHER.GOV/SEATTLE

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








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