Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 130326
AFDSEW

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

.SYNOPSIS...HIGH PRESSURE ALOFT COMBINED WITH LOW LEVEL OFFSHORE
FLOW WILL MAINTAIN SUNNY DAYS AND CLEAR NIGHTS ALONG WITH A GRADUAL
WARMING TREND THROUGH MONDAY. A CHANGE IN THIS PATTERN IS EXPECTED
STARTING MONDAY NIGHT OR TUESDAY AS THE HIGH PRESSURE ALOFT SHIFTS
INLAND AND A WEAK MARINE PUSH BEGINS. COOLER AND MORE UNSETTLED
WEATHER WILL RETURN TO THE AREA WEDNESDAY THROUGH FRIDAY AS A FEW
PACIFIC WEATHER SYSTEMS MOVE ONSHORE.

&&

.SHORT TERM...THE UPPER LEVEL RIDGE WAS ALONG 140W THIS EVENING WITH
A WEAK SHORTWAVE MOVING SE ALONG THE BC COAST IN THE NW FLOW ALOFT.
CIRRUS CLOUDS ACCOMPANY THIS SHORTWAVE. AT THE SURFACE...THERMALLY
INDUCED LOWER PRESSURE STRETCHES FROM CENTRAL VANCOUVER ISLAND ALONG
THE PACIFIC NW COAST. LOW LEVEL OFFSHORE FLOW HAS PRODUCED CLEAR
SKIES AND DROPPED DEWPOINTS AND HUMIDITIES TO THE POINT THAT IT
FEELS DESERT-LIKE...SIMILAR TO PHOENIX IN JANUARY OR EARLY FEBRUARY.

HIGHER SURFACE PRESSURE IS REBUILDING IN ALBERTA TONIGHT AND SHOULD
INCREASE OFFSHORE PRESSURE GRADIENTS A BIT INTO SATURDAY. AS THE
UPPER RIDGE SLOWLY MOVES ONSHORE SUNDAY INTO MONDAY...THE CURRENT
FORECAST OF A BIT WARMER TEMPS THROUGH THE WEEKEND LOOKS GOOD.
MONDAY MAY BE THE WARMEST DAY.

WITH THE DRY AIR MASS...WIND SHELTERED AREAS WILL TEND TO BE CHILLY
WITH READINGS DROPPING INTO THE MID 30S TO MID 40S. WINDIER
LOCATIONS WITH MIXED AIR SHOULD BE WARMER THE NEXT TWO NIGHTS. THE
SUNSHINE EACH DAY SHOULD BUMP HIGHS ABOUT 10 DEGREES ABOVE SEASONAL
AVERAGES FOR MID SEPT.

NOTE...THE STRONG SOLAR FLARE THAT OCCURRED ON WEDNESDAY COMBINED
WITH CLEAR SKIES WILL PROVIDE ABOUT THE BEST CONDITIONS POSSIBLE TO
VIEW THE AURORA BOREALIS OVER WESTERN WASHINGTON TONIGHT AND INTO
THE WEEKEND. THE ONLY FLY IN THE OINTMENT WILL BE THE INCOMING
CIRRUS CLOUDS FROM THE NW THAT COULD EITHER OBSCURE THE AURORA FOR A
WHILE AND PERHAPS ENHANCE IT AT TIMES AS WELL. FOR MORE INFORMATION
VISIT WWW.SWPC.NOAA.GOV ONLINE PARTICULARLY OVATION AURORA FORECAST
THAT IS UPDATED EVERY 30 SECONDS. BUEHNER

.LONG TERM...FROM THE PREVIOUS DISCUSSION...CHANGES IN THE WEATHER
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. THE WEAK
UPPER LOW NEAR 40/142 EJECTS INTO A SHORT WAVE TROUGH AS IT MOVES
NORTH OVER THE COASTAL WATERS WITH 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...FROM THE 315 PM AFD EDITION...THE DRY BREEZY WEATHER
OF THE LAST FEW DAYS HAS REALLY DRIED OUT THE FUELS. OF THE 41 FIRE
DANGER RATING SITES IN THE FORECAST AREA THIS AFTERNOON...ONLY 4
REMAINED BELOW THE RED FLAG DRYNESS CRITERIA - (BELLINGHAM...WHIDBEY
...FIRE TRAINING ACADEMY AND STEHEKIN.

ANOTHER AFTERNOON FRIDAY OF DRY AND BREEZY CONDITIONS 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 DOES...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 TONIGHT BUT WILL KEEP IT GOING OVER THE CENTRAL CASCADES
...THE NW 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 SATURDAY 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 READY
WITH THEIR WILDLAND FIRE RESPONSE CAPABILITIES.     HANER

&&

.AVIATION...AN UPPER RIDGE AND LOW LEVEL OFFSHORE FLOW WILL CONTINUE
TO GIVE MOSTLY CLEAR SKIES. SOME CIRRUS OVER B.C. IS DROPPING DOWN
TOWARD THE AREA IN NW FLOW ALOFT THIS EVENING.

KSEA...MOSTLY CLEAR WITH A LIGHT NLY BREEZE...SOME CIRRUS OVERNIGHT.

&&

.MARINE...THE THERMALLY INDUCED AREA OF LOWER PRESSURE OVER OREGON
THAT EXTENDS NORTH ALONG THE WA COAST WILL WEAKEN THROUGH THE
WEEKEND. THIS WILL GIVE WEAKER PRESSURE GRADIENTS AND FAIRLY LIGHT
WINDS EXCEPT FOR A FAIRLY TYPICAL DIURNAL NLY AFTERNOON BREEZE.

&&

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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