National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS66 KSEW 160342
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
845 PM PDT SAT JUN 15 2013

.SYNOPSIS...AN UPPER LEVEL LOW OFFSHORE WILL MAINTAIN WARM SOUTHERLY
FLOW ALOFT OVER WESTERN WASHINGTON THIS WEEKEND. ONSHORE FLOW WILL
CONTINUE WITH AREAS OF MORNING LOW CLOUDS SUNDAY MORNING BECOMING
MORE WIDESPREAD MONDAY MORNING. THE OFFSHORE UPPER LEVEL LOW WILL
MOVE TOWARD THE COAST ON MONDAY THEN MOVE INLAND WEDNESDAY WITH A
CHANCE OF SHOWERS AND COOLER TEMPERATURES NEXT WEEK.

&&

.SHORT TERM...THUNDERSTORMS NEVER DEVELOPED OVER THE CASCADES THIS
EVENING AND EVEN THE FEW SHOWERS SEEM TO HAVE ENDED. THERE IS A FAIR
AMOUNT OF MID AND HIGH LEVEL CLOUDINESS OVER THE AREA...AND STRATUS
HAS CREPT NORTH ALONG THE OREGON COAST TO ASTORIA. GRADIENTS ARE
ONSHORE NOW AND THIS STRATUS IS FORECAST TO SPREAD OVER THE COAST
AND SOUTHWEST TONIGHT...PROBABLY ABOUT AS FAR INLAND AS PUGET SOUND.

SUNDAY WILL BE ANOTHER WARM AND DRY DAY...EXCEPT FOR A CHANCE OF
SHOWERS OR THUNDERSTORMS OVER THE MOUNTAINS IN THE AFTERNOON AND
EVENING. EVEN MONDAY HAS A GOOD CHANCE OF BEING DRY AS THE UPPER
LEVEL LOW OFFSHORE MOVES SLOWLY TOWARD THE COAST. MODELS GENERALLY
AGREE THE UPPER LEVEL LOW WILL BE CLOSE ENOUGH TO WESTERN WASHINGTON
BY TUESDAY TO SPAWN SHOWERS. MOS POPS ARE MOSTLY IN THE LIKELY
CATEGORY TUESDAY. HIGH TEMPERATURES WILL BE MOSTLY IN THE 60S. BURKE

.LONG TERM...PREVIOUS DISCUSSION...THE GFS AND ECMWF ARE IN FAIRLY
GOOD AGREEMENT WITH THE TRANSITION OF THE UPPER LEVEL LOW ACROSS THE
AREA...TAKING IT FROM NEAR ASTORIA 12Z WEDNESDAY...TO OVER E WA 12Z
THURSDAY...AND UP OVER SE B.C. OR S ALBERTA 12Z FRIDAY. WEDNESDAY
AND THURSDAY WILL BE SHOWERY AND COOL...FIRST WITH THE LOW
OVERHEAD...THEN WITH RETURN FLOW SHOWERS THURSDAY WHEN THE LOW IS
OVER E WA. SHOWERS SHOULD BEGIN DIMINISHING FRIDAY AS THE LOW PULLS
AWAY...AND NEXT SATURDAY MAY ACTUALLY END UP BEING DRY. KAM

&&

.AVIATION...SOUTHERLY FLOW ALOFT OVER WESTERN WASHINGTON THIS
EVENING AHEAD OF AN UPPER LEVEL LOW WELL OFFSHORE. THE FLOW WILL
INCREASE SLIGHTLY TONIGHT AND SUNDAY AS THE LOW SLOWLY MOVES TOWARD
THE PACIFIC NORTHWEST. WEAK LOW LEVEL ONSHORE FLOW WILL CONTINUE.

THE AIR MASS IS SOMEWHAT MOIST AND MARGINALLY UNSTABLE WITH CUMULUS
BUILDUPS AND ISOLATED SHOWERS OVER THE CASCADES...WHICH SHOULD
DISSIPATE SHORTLY AFTER SUNSET. LOW LEVEL MOISTURE WILL RESULT IN
PATCHY STRATUS AND LOCAL MVFR AND IFR CONDITIONS LATE TONIGHT AND
SUNDAY MORNING.

KSEA...NORTHERLY WINDS 4-8 KT WILL BECOME SOUTHERLY EARLY SUNDAY
MORNING. PATCHY STRATUS COULD RESULT IN OCCASIONAL IFR CEILINGS
SUNDAY MORNING 12Z-16Z...SIMILAR TO SATURDAY MORNING.   MCDONNAL

&&

.MARINE...LIGHT NORTHWEST PRESSURE GRADIENTS WILL BECOME SOUTHWEST
TONIGHT AS WEAK LOW PRESSURE SHIFTS INTO EASTERN WASHINGTON. ONSHORE
FLOW WILL STRENGTHEN ON SUNDAY WITH SMALL CRAFT ADVISORY WINDS
LIKELY THROUGH THE CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA LATE
SUNDAY AND SUNDAY NIGHT.

A BROAD 1013 MB LOW WILL MOVE INTO THE OFFSHORE WATERS ON MONDAY...
THEN WEAKEN AND SHIFT INLAND TUESDAY. HIGH PRESSURE OVER THE
NORTHEAST PACIFIC WILL MAINTAIN ONSHORE FLOW ACROSS THE FORECAST
AREA THROUGH THE REST OF NEXT WEEK.   MCDONNAL

&&

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

&&

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