Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 260434
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 PM PST WED FEB 25 2015

.SYNOPSIS...A WEAK WEATHER SYSTEM WILL BRING RAIN AT TIMES TO
WESTERN WASHINGTON TONIGHT. RAIN WILL TRANSITION TO SHOWERS ON
THURSDAY AND PERSIST THROUGH FRIDAY. OFFSHORE FLOW AND AN UPPER
RIDGE WILL GIVE DRY WEATHER SATURDAY AND SUNDAY. A WETTER AND COOLER
PATTERN WILL RETURN EARLY NEXT WEEK.

&&

.SHORT TERM...LATEST RADAR AND OBS SHOW AREAS OF LIGHT RAIN ACROSS
WRN WA THIS EVENING. PRECIPITATION AMOUNTS SO FAR HAVE GENERALLY
BEEN UNDER ONE TENTH SINCE THIS MORNING...EXCEPT LOCALLY HIGHER
ALONG THE N COAST. SPOTTY LIGHT RAIN WILL CONTINUE THROUGH TONIGHT
AS A WEAK SURFACE TROUGH OFFSHORE DIGS SE OVER WRN WA/OREGON. SOME
WEAK CONVERGENCE IS OCCURRING AROUND THE CENTRAL PUGET SOUND
REGION...ESPECIALLY WRN KING COUNTY. THE HRRR SHOWS THIS CONTINUING
THROUGH LATE TONIGHT BEFORE DISSIPATING SO EXPECT STEADIER RAIN
AROUND SEATTLE.

MOIST NW FLOW ALOFT CONTINUES INTO THURSDAY AS A COOL UPPER TROUGH
OFF THE CENTRAL B.C. COAST BEGINS TO DIG SE TOWARD THE AREA. RAIN
WILL TRANSITION TO A MORE SHOWERY REGIME AS THE TROUGH APPROACHES
AND COOLER AIR ALOFT ARRIVES. MODELS SHOW A 500 MB -28C COLD POCKET
OVER THE REGION BY THURSDAY NIGHT SO THE ATMOSPHERE WILL BE
MARGINALLY UNSTABLE. THE CHANCE OF THUNDERSTORMS IN THE FORECAST FOR
THE COAST IS A BIT IFFY BUT WITH THE LOW OVERHEAD IT CANNOT BE RULED
OUT EITHER. WILL NOT MAKE ANY CHANGES.

SHOWERS DECREASE ON FRIDAY AS THE STACKED UPPER/SURFACE LOW SHIFT
SWD INTO OREGON. NLY FLOW WILL DEVELOP AND A 1035 MB SURFACE HIGH
WILL SETTLE INTO SRN B.C. SO EXPECT BREEZY NLY OUTFLOW WINDS TO PICK
UP. BY FRIDAY NIGHT...CLEARING SKIES ARE EXPECTED WITH COOLER
TEMPERATURES. BREEZY WINDS WILL HELP KEEP MOST PLACES JUST ABOVE
FREEZING. HOWEVER...SHELTERED LOCATIONS LIKE OLYMPIA WILL HAVE
TEMPERATURES CLOSER TO OR JUST BELOW THE FREEZING MARK SATURDAY
MORNING. LOW TEMPERATURES IN THE COLD POCKETS WILL NEED SOME
DOWNWARD ADJUSTMENT WITH THE NEXT FORECAST ISSUANCE. WITH HIGH
PRESSURE BUILDING ALOFT...CLEAR SKIES WILL PREVAIL ON SATURDAY WITH
HIGHS STRUGGLING TO REACH ABOVE 50.  MERCER

.LONG TERM...FROM PREVIOUS DISCUSSION...SUNDAY WILL BE MOSTLY SUNNY
AND TEMPERATURES WILL REBOUND A BIT. THE GFS AND EURO BOTH HAVE A
WEAK SYSTEM MOVING ALMOST DUE SOUTH ALONG THE COAST SUNDAY NIGHT AND
MONDAY. CHANCE POPS COVER THIS SYSTEM FOR NOW. AFTER IT PASSES
NORTHERLY AND OFFSHORE FLOW WILL AGAIN DEVELOP WITH MONDAY NIGHT AND
TUESDAY LOOKING BREEZY AND COOL. DRY WEATHER CONTINUES THROUGH
WEDNESDAY. HIGH TEMPERATURES ON TUESDAY AND WEDNESDAY WILL BE MOSTLY
IN THE 40S WITH LOWS IN THE 30S. BURKE

&&

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

&&

.AVIATION...NORTHWEST FLOW ALOFT. WEAK DISTURBANCES WILL MOVE SE
ACROSS THE AREA TONIGHT THROUGH THU. THEN A BROAD AND DIFFUSE 1008
MB LOW WILL MOVE SWD THROUGH THE COASTAL WATERS LATE THU NIGHT. THE
AIR MASS IS STABLE AND MOIST.

WHILE VFR CIGS AND VSBYS ARE MOST COMMON ACROSS THE AREA THIS
EVENING...CONDITIONS ARE MIXED. AN AREA OF SHOWERS ALONG THE COAST
IS GIVING LOCAL IFR CIGS AND VSBYS TO THE NORTH COAST. AN AREA OF
CONVERGENCE TO THE LEE OF THE MOUNTAINS OF VANCOUVER ISLAND IS
GIVING MVFR CIGS TO THE NORTHERN INTERIOR OF W WA FROM THE SAN JUAN
ISLANDS AND THE KBLI AREA SE INTO NORTHERN SNOHOMISH COUNTY. ANOTHER
NARROWER CONVERGENCE ZONE EXTENDS FROM E OF KSEA TO KSMP. BETWEEN
THE AREAS OF CONVERGENCE...CONDITIONS ARE VFR WITH CIGS AROUND
FL045. VIS IS OCNLY DROPPING TO 2-4 SM BR BETWEEN SHOWERS IN A FEW
SPOTS. THE LATEST HRRR SOLUTIONS SHOW ABUNDANT MVFR CIGS
DEVELOPING THIS EVENING WITH AREAS OF IFR CIGS AROUND THE AREA
THROUGH THU MORNING. IT APPEARS THAT THERE WILL BE LITTLE SKILL
IN PINPOINTING WHERE THE LOWER CLOUDS WILL DEVELOP OR MOVE WITH THE
LIGHT FLOW AND DRIPS OF PRECIPITATION.

ANOTHER WEAK FRONTAL LIKE FEATURE CAN BE SEEN EXTENDING SE FROM 50N
145W. THIS FEATURE WILL MOST LIKELY STALL ALONG THE COAST THU
AFTERNOON AND EVENING AS LOW PRES MOVING INTO THE QUEEN CHARLOTTE
SOUND MIDDAY THU DROPS SSE INTO THE COASTAL WATERS THU NIGHT. THIS
WEAK FEATURE WILL HELP TO FOCUS PRECIPITATION OVER THE OLYMPIC
PENINSULA RESULTING IN MVFR TO LOCAL IFR CONDITIONS THERE. THE
INTERIOR MAY FARE SLIGHTLY BETTER...VFR WITH OCCASIONAL MVFR CIGS
AND VIS AS FLOW BECOMES WEAKLY OFFSHORE. ALBRECHT

KSEA...CONDITIONS WILL AVERAGE P6SM BKN015 OVC040 THROUGH THU
MORNING. LOW LEVEL CONVERGENCE CENTERED NEAR THE TERMINAL WILL
GIVE LIGHT WINDS. ALBRECHT

&&

.MARINE...WEAK FRONTAL FEATURES MOVING SE THROUGH THE WATERS WILL
DISSIPATE AS THEY MOVE TO THE COASTLINE TONIGHT THROUGH THU. EXPECT
LIGHT PRES GRADIENTS ACROSS THE WATERS. A DIFFUSE AND BROAD 1008 MB
LOW WILL DROP SSE FROM THE QUEEN CHARLOTTE SOUND MIDDAY THU THROUGH
THE COASTAL WATERS LATE THU NIGHT. LIGHT FLOW WILL DOMINATE AS THE
LOW PASSES...THEN WINDS WILL TURN NELY AS THE LOW MOVES S INTO
WESTERN OREGON.

HIGH PRES WILL BUILD OVER THE INTERIOR OF BRITISH COLUMBIA FRI. AS
THE LOW LATE THU NIGHT PASSES SOUTH OF THE AREA...EXPECT N TO NE
FLOW TO INCREASE. SMALL CRAFT ADVISORY CONDITIONS ARE LIKELY OVER
MOST OF THE WATERS FRI NIGHT INTO EARLY SAT. THERE IS A SMALL CHANCE
THAT GALE FORCE WINDS WILL OCCUR AROUND THE WEST ENTRANCE TO THE
STRAIT OF JUAN DE FUCA AND OVER PORTIONS OF THE NORTHERN INLAND
WATERS FRI NIGHT.

HIGH PRES WILL MOVE INTO THE WATERS ON SUN GIVING ANOTHER PERIOD OF
LIGHT WINDS.

ANOTHER LOW WILL DROP SOUTHEAST ACROSS THE AREA SUN NIGHT INTO MON
AND WILL BE FOLLOWED BY STRONG NE PRES GRADIENTS LATER MON OR MON
NIGHT. ALBRECHT

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&

$$

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