Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 122237
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
315 PM PDT FRI SEP 12 2014

.SYNOPSIS...HIGH PRESSURE ALOFT COMBINED WITH LOW LEVEL OFFSHORE
FLOW WILL GIVE SUNNY DAYS AND CLEAR NIGHTS ALONG WITH A GRADUAL
WARMING TREND THROUGH MONDAY. A WEAK MARINE PUSH IS EXPECTED MONDAY
NIGHT OR TUESDAY AS THE UPPER LEVEL RIDGE PUSHES OFF TO THE EAST OF
THE AREA. COOLER AND MORE UNSETTLED WEATHER WILL RETURN TO THE AREA
WEDNESDAY THROUGH FRIDAY.

&&

.SHORT TERM...AN UPPER LEVEL RIDGE IS LOCATED ALONG 135W WHILE
SURFACE HIGH PRESSURE OVER BRITISH COLUMBIA IS INDUCING A THERMAL
TROUGH THAT EXTENDS FROM CENTRAL VANCOUVER ISLAND SOUTHWARD ALONG
THE WEST COAST. OFFSHORE FLOW IS GIVING SUNNY SKIES AND DRY
CONDITIONS TO WESTERN WASHINGTON...WITH RELATIVE HUMIDITY VALUES IN
PORTIONS OF WESTERN WASHINGTON BELOW 20 PERCENT THIS AFTERNOON.

EXPECT OFFSHORE PRESSURE GRADIENTS TO INCREASE SOMEWHAT TONIGHT INTO
SATURDAY AS A REINFORCING RIDGE OF HIGH PRESSURE DROPS SOUTHEASTWARD
FROM NORTHERN BRITISH COLUMBIA THROUGH ALBERTA INTO MONTANA AND
NORTH DAKOTA. THE CONTINUED OFFSHORE FLOW...COMBINED WITH THE UPPER
RIDGE OFFSHORE PUSHING GRADUALLY EASTWARD OVER THE AREA...WILL GIVE
A WARMING TREND OVER THE WEEKEND. DESPITE THE WARMING TREND
THOUGH...TEMPERATURES IN NORMALLY SHELTERED OUTLYING VALLEY
LOCATIONS WILL DROP INTO THE MID 30S TO LOWER 40S FOR THE NEXT TWO
NIGHTS. BUT IN THE DRY AIR...SUBSIDENCE AND SUNSHINE WILL ALLOW
TEMPERATURES TO RECOVER INTO THE 70S AND 80S DURING THE AFTERNOON
HOURS.

MONDAY WILL LIKELY BE THE WARMEST DAY OF THE UPCOMING WEEK AS THE
UPPER RIDGE MOVES EAST OF THE CASCADES AND THE THERMAL TROUGH SHIFTS
INLAND. HIGHS WILL LIKELY REACH INTO THE 80S ACROSS THE AREA.
PORTIONS OF THE SOUTH INTERIOR COULD FLIRT WITH THE 90 DEGREE
MARK...BUT THAT DOES BECOME HARDER TO DO AS WE MOVE THROUGH
SEPTEMBER.

NOTE...THE STRONG SOLAR FLARE THAT OCCURRED ON WEDNESDAY COMBINED
WITH CLEAR SKIES WILL INCREASE THE CHANCES OF OBSERVING AURORA
BOREALIS OVER WESTERN WASHINGTON TONIGHT AND INTO THE WEEKEND. FOR
MORE INFORMATION VISIT WWW.SWPC.NOAA.GOV ONLINE.  ALBRECHT

.LONG TERM...CHANGES IN THE PATTERN WILL BEGIN MONDAY NIGHT AS THE
UPPER RIDGE SHIFTS EAST OF THE CASCADES AND A SOUTHERLY SURGE OF
MARINE AIR MOVES UP ALONG THE COAST. MARINE AIR MAY SHIFT INLAND
MONDAY NIGHT AND TUESDAY MORNING...BUT LONG TERM MODELS DO NOT SHOW
THAT AT THIS TIME. A SHORT WAVE TROUGH LIFTING NORTHWARD OVER THE
COASTAL WATERS WILL GIVE A CHANCE OF SHOWERS OVER THE WESTERN
OLYMPIC PENINSULA TUE AND TUE NIGHT. THE GFS/ECMWF/CANADIAN
SOLUTIONS THEN ALL BRING A MORE SIGNIFICANT FALL-LIKE TROUGH THROUGH
THE AREA WEDNESDAY THROUGH FRIDAY - WITH MINOR TIMING DIFFERENCES AT
THIS TIME RANGE. CLOUDS AND POPS WERE INCREASED WEDNESDAY ONWARD AND
TEMPERATURES WERE LOWERED TO SLIGHTLY BELOW NORMAL. ALBRECHT

&&

.FIRE WEATHER...THE DRY BREEZY WEATHER OF THE LAST 2-3 DAYS HAS
REALLY DRIED OUT THE FUELS. OF THE 41 FIRE DANGER RATING SITES IN
THE FORECAST AREA...ONLY 4 REMAINED BELOW THE RED FLAG DRYNESS
CRITERIA THIS AFTERNOON (BELLINGHAM...WHIDBEY...FIRE TRAINING
ACADEMY AND STEHEKIN).

ANOTHER AFTERNOON OF DRY AND BREEZY CONDITIONS IS UNDERWAY...WITH
RELATIVE HUMIDITY VALUES IN THE TEENS ALL THE WAY OUT TO HOQUIAM.
THE THERMAL PRESSURE TROUGH NEAR THE COAST WILL PERSIST UNTIL
MID-DAY MONDAY...BUT IT WILL GRADUALLY WEAKEN. AS IT WEAKENS...THE
GENERAL TREND WILL BE FOR EAST AND NORTHEAST WINDS TO ALSO WEAKEN
THROUGH THE WEEKEND. AS SUCH...SHOULD BE SAFE TO LET THE RED FLAG
WARNING EXPIRE ALONG THE COAST LATE THIS EVENING...BUT WILL KEEP IT
GOING OVER THE CENTRAL CASCADES...THE NORTHWEST OLYMPIC PENINSULA
AND THE LOWLANDS FROM SEATTLE ON SOUTH THROUGH SATURDAY. MAY BE IN A
POSITION TO TRIM THE RFW BACK A BIT MORE AFTER TOMORROW GIVEN THE
WEAKENING TREND ON WIND.

EVEN WITH WEAKER WINDS...SOME AMOUNT OF EAST WIND WILL CONTINUE INTO
MONDAY MORNING...REINFORCING THE DRY AIR MASS AND SUPPORTING A
WARMING TREND THROUGH MONDAY. EVEN AFTER EAST WINDS END ON MONDAY
AFTERNOON...MID-LEVEL HAINES 5-6 CONDITIONS ARE EXPECTED MONDAY
AFTERNOON...INDICATING A VERY DRY AND UNSTABLE AIR MASS. THIS IS A
STRONG CONTRIBUTOR TO ACTIVE FIRE BEHAVIOR IN WESTERN
WASHINGTON...ESPECIALLY ON ELEVATED TERRAIN ABOVE ROUGHLY 1500 FEET.

NEEDLESS TO SAY...FOLKS SHOULD BE CAREFUL WITH BURNING MATERIALS
INTO EARLY NEXT WEEK...AND FIREFIGHTING AGENCIES SHOULD BE FULLY
SPUN UP WITH THEIR WILDLAND FIRE RESPONSE CAPABILITIES.     HANER

&&

.AVIATION...AN UPPER RIDGE CENTERED OFFSHORE WILL RESULT IN
CONTINUED NW FLOW ALOFT. LOW LEVEL OFFSHORE FLOW WILL ALSO PERSIST.
VFR CONDITIONS WILL PREVAIL ACROSS THE REGION THROUGH SATURDAY.

KSEA...NLY WINDS OF 10-15 KNOTS WILL GRADUALLY DIMINISH OVERNIGHT.

&&

.MARINE...THE THERMALLY INDUCED AREA OF LOW PRES JUST OFF THE
WASHINGTON COAST WILL WEAKEN ON MON. THIS WILL ALLOW A 1011 MB HIGH
TO DEVELOP OVER THE COAST ON TUE...RESULTING IN A RETURN TO LIGHT
ONSHORE FLOW.

&&

SEW WATCHES/WARNINGS/ADVISORIES...
WA...RED FLAG WARNING FOR WIND AND LOW HUMIDITY THROUGH 10 PM
      THIS EVENING IN FIRE WEATHER ZONES 649...651...AND 657.
     RED FLAG WARNING FOR WIND AND LOW HUMIDITY THROUGH 9 AM
      SATURDAY IN FIRE WEATHER ZONE 661.
     RED FLAG WARNING FOR WIND AND LOW HUMIDITY THROUGH 6 PM
      SATURDAY IN FIRE WEATHER ZONES 650...654...655...AND 659.
PZ...SMALL CRAFT ADVISORY IN EFFECT UNTIL 7 PM THIS EVENING
      FOR THE PUGET SOUND AND HOOD CANAL.

&&

$$

WWW.WEATHER.GOV/SEATTLE/

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







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