Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 111043
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
340 AM PDT THU SEP 11 2014

.SYNOPSIS...HIGH PRESSURE WILL MAINTAIN A DRY WEATHER PATTERN INTO
EARLY NEXT WEEK. LOW LEVEL OFFSHORE FLOW TODAY WILL BE STRONG ENOUGH
TO CAUSE BREEZY CONDITIONS IN THE CASCADE FOOTHILLS AND OTHER
EXPOSED LOCATIONS. ABUNDANT SUNSHINE WILL ACCOMPANY A VERY GRADUAL
WARMING TREND OVER THE WEEKEND INTO EARLY NEXT WEEK.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS CLEAR SKIES ACROSS WESTERN
WASHINGTON EARLY THIS MORNING. SURFACE GRADIENTS HAVE TURNED STRONG
OFFSHORE WITH KUIL-KBLI NEAR -3 MB AND THE CROSS CASCADE GRADIENT
DOWN TO -4 MB AND DROPPING. EASTERLY WINDS HAVE NOT REALLY PICK UP
YET IN THE CASCADE FOOTHILLS WITH ONLY ENUMCLAW REPORTING A GUST TO
20 MPH AT 3 AM. WITH THE OFFSHORE FLOW DEW POINT HAVE TUMBLED
OVERNIGHT WITH 30S AND LOWER 40S COMMON. WITH THE DRY AIR OVER THE
AREA THERE WAS A WIDE VARIETY OF TEMPERATURES ACROSS THE AREA
DEPENDING ON IF THE LOCATION WAS SHELTERED FROM THE WIND OR NOT.
TEMPERATURES IN THE WIND SHELTERED AREAS WERE AS LOW AS AROUND 40
WHILE IN THE WINDIER LOCATIONS TEMPERATURES WERE NEAR 60 AT 3 AM.

LITTLE CHANGE THE FORECAST THIS MORNING WITH THE LOW LEVEL OFFSHORE
FLOW PEAKING LATE THIS MORNING AS AN AREA OF HIGH PRESSURE DROPS
SOUTH ALONG THE FRONT RANGE OF THE ROCKIES IN MONTANA. WITH THE
INCREASING OFFSHORE FLOW THIS MORNING BREEZY EAST WINDS WILL DEVELOP
IN THE CASCADE FOOTHILLS AND CONTINUE INTO THE AFTERNOON HOURS.
TEMPERATURES ALOFT ARE NOT VERY WARM OVER THE AREA TODAY WITH THE
850 MB TEMPERATURES AROUND PLUS 10C. EVEN WITH THE INCREASING
OFFSHORE FLOW WITH THESE TEMPERATURES ALOFT EXPECT HIGHS TO BE
MOSTLY IN THE 70S TODAY. THE WARMEST LOCATIONS WILL BE AREAS EXPOSED
TO THE DOWNSLOPE EAST WINDS...THE CASCADE AND OLYMPIC FOOTHILLS FOR
THE MOST PART.

OFFSHORE FLOW PATTERN CONTINUING TONIGHT AND FRIDAY WITH AN UPPER
LEVEL RIDGE WELL OFFSHORE AND A THERMALLY INDUCED TROUGH ALONG THE
COAST. THE OFFSHORE FLOW WILL BE A LITTLE WEAKER WITH THE SURFACE
HIGH WEAKENING EAST OF THE CASCADES. LOWS TONIGHT WILL ONCE AGAIN
WILL BE IN A WIDE RANGE WITH THE WIND PROTECTED AREAS DROPPING INTO
THE MID 30S WHILE LOCATIONS THAT WITH SOME WIND WILL STAY UP IN THE
50S. TEMPERATURES ALOFT START TO WARM UP ON FRIDAY WITH 850 MB
TEMPERATURES PLUS 12C TO PLUS 14C BY 00Z SATURDAY. THE WARMER
TEMPERATURES ALOFT WITH BE COUNTERACTED A LITTLE BE THE WEAKENING
OFFSHORE FLOW. END RESULT WILL BE HIGHS ON FRIDAY NEAR OR A COUPLE
OF DEGREES WARMER THAT TODAY...70S AND LOWER 80S FOR MOST LOCATIONS.

LITTLE CHANGE IN THE PATTERN FRIDAY NIGHT AND SATURDAY WITH THE
UPPER LEVEL RIDGE OFFSHORE SLOWLY MOVING EAST WITH WEAK LOW LEVEL
OFFSHORE FLOW CONTINUING OVER THE AREA. TEMPERATURES ALOFT WARM
ANOTHER COUPLE OF DEGREES C ON SATURDAY SO EXPECT UP TO 5 DEGREES OF
WARMING WITH THE WARMER LOCATIONS LIKE THE SOUTHWEST INTERIOR
PUSHING THE MID 80S.

**NOTE...THE STRONG SOLAR FLARE THAT OCCURRED YESTERDAY WILL
INCREASE THE CHANCES OF SEEING THE AURORA BOREALIS OVER WESTERN
WASHINGTON TOMORROW NIGHT INTO THE WEEKEND. FOR MORE INFORMATION GO
TO WWW.SWPC.NOAA.GOV

.LONG TERM...EXTENDED MODELS IN GOOD AGREEMENT WITH THE UPPER LEVEL
RIDGE CONTINUING TO DRIFT EAST ON SUNDAY WITH THE RIDGE AXIS STILL
OFFSHORE AT 00Z MONDAY. LIGHT OFFSHORE FLOW ALSO CONTINUING ON
SUNDAY WITH THE TEMPERATURES ALOFT WARMING ANOTHER COUPLE OF DEGREES
C. THIS WILL RESULT IN SLIGHTLY WARMER MAX TEMPERATURES ON SUNDAY.
RIDGE AXIS MOVING OVERHEAD ON MONDAY WITH THE THERMALLY INDUCED
TROUGH MOVING INLAND. THIS WILL ALLOW AN AFTERNOON SEABREEZE TO KICK
UP ALONG THE COAST LOWERING THE MAX TEMPERATURES BY 5 TO 10 DEGREES.
LITTLE CHANGE IN THE MAX TEMPS ON MONDAY FOR THE INTERIOR. PATTERN
STARTS TO BREAK DOWN ON TUESDAY WITH THE UPPER LEVEL RIDGE AXIS EAST
OF THE AREA. THERMALLY INDUCED TROUGH ALSO MOVING INTO EASTERN
WASHINGTON BY THE 00Z WEDNESDAY. TEMPERATURES ALOFT ARE STILL WARM
OVER THE AREA WITH MODEL 850 MB TEMPERATURES STILL PLUS 14 TO 17C.
FOR NOW WILL GO WITH A VERY WEAK PUSH SCENARIO WITH HIGHS ON TUESDAY
UP TO 5 DEGREES COOLER FOR THE INTERIOR. MODEL CONSENSUS BREAKS DOWN
ON WEDNESDAY WITH THE ECMWF AND CANADIAN KEEPING THE NEXT SYSTEM TO
REACH THE AREA OFFSHORE WHILE THE GFS HAS PRECIPITATION MOVING INTO
WESTERN WASHINGTON IN THE AFTERNOON AND OVER MOST OF THE AREA BY 06Z
THURSDAY. CURRENT FORECAST IS MORE IN LINE WITH THE GFS. IF THE
MODEL TRENDS CONTINUE LOOK FOR THE CHANCE OF SHOWERS TO BE TAKEN OUT
OF THE WEDNESDAY FORECAST. FELTON

&&

.FIRE WEATHER...PREVIOUS DISCUSSION...NORTHEAST-EAST PRESSURE
GRADIENTS WILL BECOME TIGHTLY PACKED ACROSS THE AREA EARLY THIS
MORNING...INDUCING ENOUGH E-NE WIND AND LOW HUMIDITY TODAY AND
POSSIBLY FRIDAY TO EASILY EXCEED RED FLAG WIND AND HUMIDITY
CRITERIA. IN GENERAL...FUELS ARE TOO MOIST OVER THE NORTH INTERIOR
AND THE NORTH CASCADES TO WARRANT A RFW...BUT FUELS ARE DRY ENOUGH
TO REACH CRITERIA WITH A COUPLE DAYS OF WARM AND DRY WEATHER SOUTH
OF A LINE FROM SILVERDALE TO ENUMCLAW TO STAMPEDE PASS...AND OVER
THE OLYMPIC PENINSULA. OF COURSE...LIGHT FUELS WILL BE THE QUICKEST
TO DRY OUT. THE COMBINATION OF WIND AND LOW HUMIDITY TODAY AND
FRIDAY WILL CAUSE RAPID RATES OF SPREAD ON ANY FIRES THAT GET
STARTED...ESPECIALLY IN LIGHT FUELS SUCH AS TALL BROWN GRASS.

ON A DAY-TO-DAY SCALE...EAST WINDS WILL GRADUALLY EASE OVER THE
WEEKEND...BUT A WARM AND DRY AIR MASS WILL REMAIN IN PLACE. POOR
NIGHTTIME HUMIDITY RECOVERY WILL CONTINUE THROUGH MONDAY NIGHT ON
ELEVATED TERRAIN ABOVE RADIATION INVERSIONS. MID-LEVEL HAINES 5-6
CONDITIONS WILL BE PREVALENT ON SUNDAY AND MONDAY...INDICATING VERY
DRY AND SOMEWHAT UNSTABLE CONDITIONS IN THE 850-700 MB LAYER. THOSE
ATMOSPHERIC CONDITIONS SUPPORT AN ACTIVE BURNING ENVIRONMENT.
HANER

&&

.AVIATION...AN UPPER LEVEL RIDGE ANCHORED AT 135W WILL HELP KEEP
NORTHWESTERLY FLOW ALOFT OVER WASHINGTON THROUGH FRIDAY. THE AIR
MASS IS DRY AND STABLE WITH CLEAR SKIES...VFR CONDITIONS WILL
PERSIST THROUGH FRIDAY.

THE THERMALLY INDUCED SURFACE TROUGH ALONG THE OREGON AND WASHINGTON
COASTS AND HIGH PRESSURE OVER EASTERN BRITISH COLUMBIA AND ALBERTA
IS SUPPORTING OFFSHORE AND NORTHERLY LOW LEVEL FLOW THIS MORNING.
THE SURFACE HIGH PRESSURE OVER CANADA WILL CONTINUE TO SHIFT SOUTH
INTO EASTERN WASHINGTON THIS MORNING...HELPING SURFACE GRADIENTS
BECOME MORE EASTERLY AND SOLIDLY OFFSHORE.

KSEA...SKIES WILL REMAIN CLEAR AND VFR TODAY. NORTHEAST WINDS 10-15
KT WILL BECOME NORTHERLY AFTER 21Z/2PM.

&&

.MARINE...LOW LEVEL FLOW WILL REMAIN OFFSHORE AND NORTHERLY THROUGH
THE END OF THE WEEK. EXPECT SMALL CRAFT ADVISORY EASTERLIES AT
THE WEST ENTRANCE AT TIMES THIS MORNING...EASING THIS AFTERNOON.

&&

SEW WATCHES/WARNINGS/ADVISORIES...
WA...RED FLAG WARNING FOR WIND AND LOW HUMIDITY THROUGH FRIDAY IN
     FIRE WEATHER ZONES 649...650...651...654...655...657...659 AND
     661.
PZ...SMALL CRAFT ADVISORY WEST ENTRANCE TO THE STRAIT OF JUAN DE
     FUCA...AND NORTHERN INNER COASTAL WATERS.

&&

$$

WWW.WEATHER.GOV/SEATTLE/

YOU CAN SEE AN ILLUSTRATED VERSION OF THIS FORECAST DISCUSSION AT
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