Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 011010
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
310 AM PDT FRI AUG 1 2014

.SYNOPSIS...A LARGE UPPER LEVEL RIDGE WILL REMAIN OVER THE PACIFIC
NORTHWEST INTO NEXT WEEK. A SMALL WEAK UPPER LEVEL TROUGH WILL MOVE
UP OVER WESTERN WASHINGTON TODAY FOR A CHANCE OF THUNDERSTORMS.
ONSHORE FLOW WILL BRING AREAS OF LATE NIGHT AND MORNING CLOUDS WITH
MOSTLY SUNNY AND WARM AFTERNOONS FROM SATURDAY ONWARD.

&&

.SHORT TERM...A LARGE UPPER LEVEL RIDGE WILL REMAIN OVER THE PACIFIC
NORTHWEST FOR THE NEXT WEEK...MAINTAINING A WARM AIR MASS OVER THE
REGION FOR WARMER TEMPERATURES THAN NORMAL.

THE MAIN FORECAST PROBLEM FOR TODAY THROUGH SATURDAY IS THE CHANCE
OF THUNDERSTORMS AND THEIR COVERAGE OVER W WA. A WEAK UPPER LEVEL
SHORTWAVE TROUGH OVER WESTERN OREGON WILL MOVE SLOWLY NORTHWARD OVER
SW WA TODAY...THEN WILL REMAIN OVER THE GENERAL AREA THROUGH SUNDAY
WHILE MOVING SLOWLY NE. THE SHORTWAVE TROUGH HAS BEEN DOING A NICE
JOB OF DESTABILIZING THE AIR MASS OVER NW OREGON
OVERNIGHT...RESULTING IN SCATTERED THUNDERSTORMS...LOCALIZED HEAVY
SHOWERS AND QUITE A BIT OF LIGHTNING.

UNFORTUNATELY THE MODELS HAVE BEEN ERRATIC WITH THE FINER FORECAST
DETAILS...WHICH COULD HAVE GIVEN MORE CONFIDENCE IN THE THUNDERSTORM
FORECAST FOR THE W WA LOWLANDS TODAY. IF YOU GO BY THE MOST RECENT
MODEL SOLUTIONS...THE CURRENT FORECAST SEEMS TO COVER TOO MUCH OF
THE INTERIOR LOWLANDS WITH THUNDERSTORMS TODAY. HOWEVER THE
THUNDERSTORMS PRESENTLY OVER THE W OREGON LOWLANDS CASTS DOUBT ON
THOSE SAME MODEL SOLUTIONS. THE BEST COURSE IS TO STICK WITH THE
CURRENT FORECAST...EVEN WITH LOW CONFIDENCE. THE SHORTWAVE TROUGH
WILL REMAIN IN THE AREA ON SATURDAY...BUT BY THEN THE MOST UNSTABLE
AIR MASS SHOULD BE OVER THE MOUNTAINS. WITH THE TROUGH MOVING NE
ONLY THE N CASCADES SHOULD BE UNSTABLE ENOUGH FOR THUNDERSTORMS ON
SUNDAY.

QUITE A LOT OF MID AND HIGH LEVEL CLOUD COVER OVER OREGON THIS
MORNING WILL MOVE UP OVER W WA TODAY FOR PARTLY SUNNY SKIES AT BEST.

W WA AND THE COASTAL WATERS REMAIN PRETTY MUCH STRATUS FREE THIS
MORNING. THE NAM HAS BEEN CONSISTENT IN DEVELOPING STRATUS OVER THE
COASTAL WATERS TODAY...WITH ONSHORE FLOW SPREADING IT INLAND OVER
MUCH OF THE INTERIOR LATE TONIGHT AND SATURDAY MORNING. ONSHORE FLOW
WILL CONTINUE THIS WEEKEND FOR A BIT MORE STRATUS COVERAGE SUNDAY
MORNING. THE WARM AIR MASS UNDER THE UPPER LEVEL RIDGE WILL KEEP
INLAND TEMPERATURES IN THE MID 70S TO MID 80S THROUGH THE WEEKEND.
THE MID AND HIGH CLOUDS OVER THE AREA WILL KNOCK A FEW DEGREES OFF
MAX TEMPS TODAY...AND MORNING STRATUS SHOULD DO THE SAME SATURDAY
AND SUNDAY. KAM

.LONG TERM...THIS WEEKENDS SHORTWAVE TROUGH WILL BE FAR ENOUGH NE OF
THE AREA BY MONDAY TO KEEP THUNDERSTORMS OUT OF THE FORECAST. AS THE
TROUGH DEPARTS...THE UPPER LEVEL RIDGE WILL REBUILD A LITTLE FOR
SLIGHTLY WARMER MAX TEMPS ON MONDAY. A FLAT UPPER LEVEL RIDGE WILL
REMAIN OVER THE REGION THROUGH MID WEEK WITH 500 MB HEIGHTS AROUND
5850 METERS. THIS SHOULD KEEP THE AIR MASS WARM AND DRY FOR LITTLE
CHANGE IN MAX TEMPS. WEAK ONSHORE FLOW WILL CONTINUE TO BRING
MORNING LOW CLOUDS TO THE AREA AND PROVIDE A LITTLE COOLING. THE GFS
AND ECMWF SEEM TO BRING A WEAK SYSTEM JUST OFFSHORE ON TUESDAY
BEFORE ALLOWING IT TO DISSIPATE. KAM

&&

.AVIATION...A RIDGE IS OVER THE WRN U.S. WITH SSW FLOW ALOFT OVER
WA. AT THE SURFACE THERE IS HIGH PRESSURE OFFSHORE WITH THERMAL LOW
PRESSURE INLAND. A DISTURBANCE OVER OREGON WILL MOVE NORTH AND SOME
MOISTURE AND INSTABILITY WILL REACH WRN WA TODAY. THERE WILL BE SOME
MID AND HIGH CLOUDS AND PERHAPS ACCAS WITH A CHANCE OF TSTMS...THE
BEST CHANCE OF TSTMS WILL BE OVER THE CASCADES. PATCHY FOG WILL BE
CONFINED TO THE COAST THIS MORNING.

AT 3 AM THERE WAS A THUNDERSTORM NEAR SCAPPOOSE OREGON WHICH HAD 34
LIGHTNING STRIKES IN JUST 15 MINUTES.

KSEA...MID AND HIGH CLOUDS WILL INCREASE AND THERE IS A CHANCE OF
THUNDERSTORMS...MAINLY EAST OF THE AREA LATER THIS MORNING. THE
CHANCE OF A STORM OVER SEATTLE IS PRETTY LOW BUT IT WILL BE WORTH
WATCHING THE RADAR THIS MORNING TO SEE IF THE STORMS OVER NW OREGON
MAKE IT CLOSER TO THE METRO AREA LATER THIS MORNING.

&&

.MARINE...HIGH PRESSURE IS OVER THE OFFSHORE WATERS WITH THERMAL LOW
PRESSURE EAST OF THE CASCADES. A WEATHER DISTURBANCE OVER OREGON
MOVING NORTH WILL GIVE A CHANCE OF THUNDERSTORMS...MAINLY INLAND
WATERS TODAY. A FAIRLY STRONG SUMMERTIME WESTERLY SEA BREEZE FLOW IN
THE STRAIT OF JUAN DE FUCA COULD GIVE WESTERLY GALES THIS
EVENING...WITH THE BEST CHANCE IN THE CENTRAL STRAIT BUT THE WRFGFS
DOES NOT SHOW PARTICULARLY STRONG WINDS THIS EVENING SO WILL JUST
LEAVE THE GALE WATCH UP AND SIMPLY FORECAST SMALL CRAFT ADVISORY
STRENGTH WINDS FOR NOW.

&&

.FIRE WEATHER...PREVIOUS DISCUSSION FROM THURSDAY AFTERNOON.
ELEVATED THUNDERSTORMS COULD MOVE UP INTO INTERIOR OF WESTERN
WASHINGTON ON FRIDAY MORNING. HARD TO PIN DOWN EXACTLY WHICH ZONES
WILL BE AFFECTED...BUT CONFIDENCE HIGH ENOUGH TO ADD THUNDERSTORMS
TO THE FORECAST FOR ALL BUT THE COAST AND WESTERN OLYMPIC MOUNTAINS.
IN THE AFTERNOON...SURFACE-BASED THUNDERSTORMS MAY DEVELOP OVER THE
HIGHEST MOUNTAIN PEAKS...WITH STORM MOTION FROM SOUTH TO NORTH.

SINCE THE HEAVY RAINS LAST WEEK...FUELS HAVE DRIED TO PRE-REQUISITE
DRYNESS NEEDED TO CONSIDER RED FLAG WARNINGS IN LOWLANDS ZONES FROM
SEATTLE ON SOUTH...OVER THE EASTERN OLYMPIC MOUNTAINS...AND IN THE
STEHEKIN AREA. FUELS REMAIN TOO MOIST IN OTHER LOCATIONS SUCH AS THE
NORTH INTERIOR...WESTERN OLYMPIC PENINSULA AND WEST SLOPES OF THE
CASCADES. HAVE ISSUED A FIRE WEATHER WATCH FOR THE EAST SIDE OF
NORTH CASCADES NATIONAL PARK (STEHEKIN AREA)...WHICH IS THE ONLY
ZONE WHERE FUELS ARE DRY ENOUGH AND THE CONFIDENCE FOR SCATTERED
LIGHTNING ON FRIDAY IS HIGH ENOUGH FOR SUCH AN ISSUANCE. OF
COURSE...A FIRE WEATHER WATCH OFTEN PRECEDES A RED FLAG WARNING.
OVER THE INTERIOR LOWLANDS OF WESTERN WASHINGTON...MERELY CALLING
FOR ISOLATED LIGHTNING...WHICH IS NOT WIDESPREAD ENOUGH TO WARRANT A
RED FLAG WARNING.    HANER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...GALE WARNING CENTRAL STRAIT OF JUAN DE FUCA.
     SMALL CRAFT ADVISORY EAST ENTRANCE TO THE STRAIT OF JUAN DE
       FUCA...COASTAL WATERS FROM JAMES ISLAND TO CAPE SHOALWATER OUT
       TO 10 NM.
     GALE WATCH LATE FRIDAY AFTERNOON AND FRIDAY NIGHT FOR THE
       CENTRAL STRAIT OF JUAN DE FUCA AND EAST ENTRANCE STRAIT.

&&

$$

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








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