Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 180318
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
818 PM PDT SUN AUG 17 2014

.SYNOPSIS...A WEAK UPPER LOW OVER THE AREA WILL CONTINUE DRIFTING
SOUTH OVERNIGHT. WEAK HIGH PRESSURE ALOFT WILL MONDAY. EXPECT A
LOW PRESSURE SYSTEM TO DOMINATE THE WEATHER PATTERN OVER THE
REGION TUESDAY AND WEDNESDAY. THE MAIN IMPACT THIS SYSTEM WILL
HAVE ON OUR WEATHER WILL BE COOLER AND CLOUDIER DAYS.

&&

.SHORT TERM...
A WEAK UPPER LOW OVER WRN WA WILL CONTINUE TO DRIFT SOUTH
OVERNIGHT. THIS LOW WILL BE OFF THE FAR NORTHERN CA COAST BY
MIDDAY MON. WEAK HIGH PRESSURE ALOFT WILL PREVAIL OVER THE CWA
DURING THE DAY MON. THE AIR MASS WILL BECOME SLIGHTLY UNSTABLE
OVER THE CASCADES MON AFTERNOON...THUS CANNOT COMPLETELY RULE OUT
THE POSSIBILITY OF ISOLATED SHOWERS OR TSTMS NEAR THE CASCADE
CREST.

AN UPPER TROF WILL DIG OVER THE PACIFIC NORTHWEST MON NIGHT AND
TUE. THE MAIN IMPACT THIS WILL HAVE ON OUR WEATHER WILL BE TO
STRENGTHEN THE LOW LEVEL ONSHORE PRES GRADIENT AND DEEPEN THE
MARINE LAYER.

LITTLE CHANGE IS ANTICIPATED IN THE OVERALL SYNOPTIC SCALE
PATTERN ON WED. WESTERN WA WILL REMAIN UNDER THE INFLUENCE OF
AN UPPER TROF. THIS WILL RESULT IN SLIGHTLY BELOW NORMAL DAYTIME
TEMPS AND MORE CLOUD COVER. ALSO...CANNOT RULE OUT ISOLATED
SHOWERS OR AREAS OF MORNING DRIZZLE.

.LONG TERM FROM THE PREV DISCUSSION...
GFS AND ECMWF MAINTAINED A LONG WAVE UPPER LEVEL TROUGH CENTERED
OVER EASTERN WA THROUGH FRIDAY...THEN SHIFTED IT EASTWARD NEXT
WEEKEND. NW FLOW ALOFT CONTINUED OVER W WA WITH PASSING SHORTWAVE
TROUGHS BRUSHING MAINLY THE N CASCADES WITH A FEW SHOWERS. THE
MODELS SEEMED TO HAVE SETTLED DOWN WITH THIS DRIER FORECAST FOR
THE LOWLANDS BUT CONFIDENCE WAS STILL A LITTLE SHAKY GIVEN THE
RECENT MODEL WOBBLES. ONSHORE FLOW WILL BE A LITTLE STRONGER AND
MORE SOUTHWESTERLY...SO MORNING STRATUS WILL BE A REGULAR VISITOR.
THE PRESENCE OF THE UPPER TROUGH AND THE SW ONSHORE FLOW WILL KEEP
MAX TEMPS NEAR OR SLIGHTLY BELOW NORMAL. THE ECMWF HAD AN OFFSHORE
RIDGE BUILDING INLAND A LITTLE NEXT WEEKEND...FOR SOME DRYING AND
WARMING...BUT THE GFS KEPT THE RIDGE OFFSHORE. FORECAST FOLLOWED
THE ECMWF FOR NOW. KAM

&&

.AVIATION...A VERY WEAK UPPER LEVEL LOW OVER THE PACIFIC NORTHWEST
WILL SHIFT INLAND TONIGHT AND MONDAY WITH INCREASING WESTERLY FLOW
ALOFT. AT THE SURFACE...ONSHORE FLOW WILL CONTINUE WITH HIGH
PRESSURE OFFSHORE AND LOWER PRESSURE INLAND. AIR MASS STABLE EXCEPT
SLIGHTLY UNSTABLE NEAR THE CASCADE CREST. COASTAL STRATUS AND FOG
WILL ONCE AGAIN PUSH PARTLY INLAND TONIGHT...MAINLY DOWN THE STRAIT
OF JUAN DE FUCA...THEN BURN BACK TO THE COAST ON MONDAY.

KSEA...MOSTLY CLEAR SKIES. FOG AND LOW CLOUDS NOT EXPECTED TO REACH
THE TERMINAL MONDAY MORNING. NORTHERLY WIND 4-8 KNOTS. SCHNEIDER

&&

.MARINE...ONSHORE FLOW WILL PERSIST FOR THE NEXT SEVERAL DAYS WITH
HIGH PRESSURE OFFSHORE AND LOWER PRESSURE INLAND. THIS WILL BRING
MARGINAL SMALL CRAFT ADVISORY WEST WINDS TO THE STRAIT OF JUAN DE
FUCA THE NEXT COUPLE OF EVENINGS. AN UPPER LEVEL DISTURBANCE PASSING
TO THE NORTH MONDAY NIGHT AND TUESDAY WILL BOOST NORTHWEST WINDS
OVER THE COASTAL WATERS TUESDAY...AS WELL AS ONSHORE FLOW THROUGH
THE STRAIT TUESDAY NIGHT. GALE FORCE WEST WINDS REMAIN POSSIBLE FOR
THE CENTRAL AND EASTERN STRAIT TUESDAY EVENING. SCHNEIDER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY IN EFFECT FOR THE CENTRAL/EASTERN STRAIT
     OF JUAN DE FUCA AND THE COASTAL WATERS FROM JAMES ISLAND TO
     CAPE SHOALWATER FROM 10 NM OUT TO 60 NM.


&&

$$

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