Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 272303
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PST FRI FEB 27 2015

.SYNOPSIS...SHOWERS WILL END TONIGHT AS DRIER NORTHERLY FLOW ALOFT
AND LOW LEVEL OFFSHORE FLOW DEVELOPS. THE UPPER RIDGE AND OFFSHORE
FLOW WILL BRING SUNNY DAYS AND COOL NIGHTS THIS WEEKEND. A WEAK
SYSTEM WILL MOVE THROUGH SUNDAY NIGHT AND MONDAY...WITH DRY WEATHER
AGAIN TUESDAY AND WEDNESDAY.

&&

.SHORT TERM...AN UPPER LOW OVER NORTHWEST OREGON WILL SHIFT SOUTH
TONIGHT. SHOWERS WILL CONTINUE TO DECREASE ACROSS THE AREA THIS
EVENING AS THE UPPER LOW PULLS AWAY. SHOWERS SHOULD PRETTY MUCH COME
TO AN END AFTER MIDNIGHT TONIGHT AS DRIER NORTHERLY FLOW ALOFT AND
LOW LEVEL OFFSHORE FLOW DEVELOP.

A SURFACE HIGH MOVING INTO SOUTHERN BRITISH COLUMBIA WILL RESULT IN
LOCALLY BREEZY NORTHERLY WINDS TONIGHT AND SATURDAY. OTHERWISE...
SATURDAY SHOULD BE A SUNNY DAY AFTER SOME LINGERING EARLY MORNING
CLOUDS. SUNDAY SHOULD BE ANOTHER SUNNY DAY.

LOW LEVEL OFFSHORE FLOW WILL WEAKEN AND THE FLOW ALOFT WILL BACK TO
NORTHWEST ON WEDNESDAY AS A WEATHER SYSTEM APPROACHES FROM THE
NORTHWEST FOR LESS WIND. THIS WEATHER SYSTEM WILL DROP DOWN FROM THE
NORTHWEST SUNDAY NIGHT AND MONDAY...BRINGING CLOUDS. THE ECMWF SHOWS
RAIN ALL AREAS WITH THIS FEATURE BUT THE GFS JUST HAS SPOTTY
PRECIPITATION AND THE GEM IS DRY. THE FORECAST IS A BLEND OF THESE
MODELS FOR NOW WHICH MEANS MOSTLY CLOUDY WITH A CHANCE OF RAIN.
SCHNEIDER

.LONG TERM...AN UPPER RIDGE WILL BE OVER THE NORTHEAST PACIFIC
TUESDAY AND WEDNESDAY...GIVING DRY NORTHERLY FLOW ALOFT TO WESTERN
WASHINGTON. THERE WILL BE SOME BREEZY NORTH WINDS TUESDAY AS A
SURFACE HIGH MOVES INTO SOUTHERN BRITISH COLUMBIA...THEN LESS WIND
WEDNESDAY AS THE HIGH SHIFTS SOUTHEAST.

MODELS SHOW THE UPPER RIDGE WEAKENING A BIT THURSDAY WITH A WARM
FRONT MOVING OVER THE TOP. THIS WILL BRING SOME CLOUDS TO THE AREA
AND PERHAPS A CHANCE OF RAIN...WITH THE BEST CHANCES COAST AND FAR
NORTH. A COLD FRONT WILL APPROACH FROM THE WEST ON FRIDAY. THIS DAY
COULD WIND UP BEING DRY BUT A CHANCE OF RAIN CANNOT BE COMPLETELY
RULED OUT FOR NOW. SCHNEIDER

&&

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

&&

.AVIATION...A SMALL UPPER LEVEL AND SURFACE LOW NEAR ASTORIA AT 22Z
WILL MOVE S OVER N CA BY 12Z. DRIER N-NE FLOW SURFACE AND ALOFT WILL
GRADUALLY PUSH S OVER W WA TONIGHT AS AN UPPER LEVEL RIDGE MOVES
OVER N B.C. AND A SURFACE RIDGE MOVES OVER S B.C.

RAIN IS BEGINNING TO DIMINISH OVER THE N INTERIOR THIS AFTERNOON
WHILE SHOWERS HAVE DEVELOPED OVER THE SW INTERIOR. THIS HAS ALLOWED
A MIX OF CLOUD LAYERS TO PERSIST OVER W WA. VFR CONDITIONS
PREDOMINATE OVER THE N INTERIOR BUT A MIX OF VFR AND IFR CIGS IS
STILL PRESENT OVER PUGET SOUND AND THE SW INTERIOR. LATEST MODELS
STILL INDICATE DECREASING MOISTURE FROM THE N ACROSS THE AREA
TONIGHT...BUT PROBABLY A LITTLE SLOWER THAN PREVIOUSLY EXPECTED. THE
SURFACE RIDGE OVER S B.C. WILL INCREASE N-NE SURFACE WINDS ACROSS W
WA THROUGH 06Z WITH LOCALLY WINDY CONDITIONS CONTINUING THROUGH
18Z...PARTICULARLY OVER THE N INTERIOR. WITH AN UPPER LEVEL RIDGE
OVER B.C. ON SATURDAY AND DRY N-NE FLOW ALOFT...GOOD VFR CONDITIONS
ARE EXPECTED.

KSEA...CIGS AT KSEA ARE EXPECTED TO REMAIN VFR...GENERALLY
BKN-OVC050 AND HIGHER THROUGH 09Z...WITH CLOUD LAYERS BECOMING
SCATTERED AFTER 09Z. N-NE SURFACE WINDS WILL REMAIN 5-10 KT THROUGH
09Z...INCREASING TO 10-15 AFTER 09Z. THE INCREASE IN SURFACE WINDS
WILL PROVIDE ENOUGH MIXING TO PRECLUDE FOG FROM FORMING. KAM

&&

.MARINE...A 1006 MB SURFACE LOW NEAR ASTORIA AT 22Z WILL MOVE S OVER
N CA BY 12Z SATURDAY. MODERATE N-NE SURFACE FLOW WILL DEVELOP THIS
EVENING AS A SURFACE RIDGE MOVES DOWN OVER SOUTHERN B.C. BEHIND THE
LOW. SMALL CRAFT ADVISORIES ARE IN EFFECT FOR ALL WATERS FOR THE
N-NE SURFACE WINDS. MOST AREAS SHOULD REMAIN IN THE 15-25
RANGE...BUT THE N INLAND WATERS AND THE E ENTRANCE SHOULD BE A
LITTLE STRONGER. THE CANADIAN MESOSCALE MODEL IS STILL THE ONLY ONE
THAT SHOWS 30-35 KT GALE WINDS OVER THE N INLAND AND E ENTRANCE FROM
06Z-12Z...SO I WILL STICK WITH THE CONSENSUS AND KEEP WINDS 30 KT OR
BELOW.

SURFACE WINDS WILL GRADUALLY DIMINISH SATURDAY AS THE SURFACE RIDGE
SETTLES OVER W WA.

MODELS SHOW AN UPPER LEVEL AND SURFACE TROUGH MOVING S ACROSS THE
AREA SUNDAY NIGHT. THE WRF-GFS INDICATED A BRIEF PERIOD OF NORTHERLY
SCA WINDS MAINLY OVER THE COASTAL WATERS AND THROUGH PUGET SOUND
IMMEDIATELY BEHIND THIS FEATURE. ANOTHER SURFACE RIDGE WILL MOVE
DOWN OVER B.C. MONDAY NIGHT AND TUESDAY FOR ANOTHER PERIOD OF
MODERATE E-NE FLOW. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY ALL WATERS.

&&

$$

YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML











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