Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 042250 AAA
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
350 PM PDT FRI SEP 4 2015

.SYNOPSIS...AN UPPER LEVEL LOW WILL DEPART AND AN UPPER LEVEL RIDGE
WILL BRING DRY AND WARMER WEATHER TO WESTERN WASHINGTON ON SATURDAY.
A WEAK FRONT WILL BRING SOME RAIN TO THE AREA ON SUNDAY. DRY WEATHER
WILL RETURN FOR LABOR DAY. A WEAK FRONT WILL BRUSH THE NORTH PART OF
WESTERN WASHINGTON ON TUESDAY FOR A CHANCE OF RAIN THERE. STRONGER
HIGH PRESSURE WILL BUILD STARTING AROUND THE MIDDLE OF NEXT WEEK.

&&

.SHORT TERM...THERE WERE SCATTERED SHOWERS OVER THE CASCADES THIS
AFTERNOON AND A FEW SHOWERS OVER THE OLYMPICS AND SW WA. A GOOD PORTION
OF WRN WA WAS CLEARING. THE UPPER LOW WILL BE REPLACED BY A WEAK UPPER
RIDGE SATURDAY FOR A DAY WARMER AND SUNNIER WEATHER. A FRONT WILL BRING
CLOUDS AND SOME RAIN TO WRN WA ON SUNDAY. LOW LEVEL ONSHORE FLOW BEHIND
THE FRONT LATER SAT WILL KEEP A CHANCE OF SHOWERS IN THE FORECAST AND A
PSCZ MIGHT FORM IN THE SEATTLE AREA SATURDAY EVENING. NORTHERLY FLOW
WILL DEVELOP FOR LABOR DAY AS AN UPPER RIDGE BUILDS OFFSHORE.
ANOTHER FRONT WILL BRUSH THE AREA ON TUESDAY. THE 18Z GFS IS WETTER
WITH THIS SYSTEM THAN THE PREVIOUS RUN.

.LONG TERM...WARMER SUNNIER WEATHER IS LIKELY FOR THE LATTER HALF OF
THE WEEK AS UPPER HEIGHTS CREEP UP AND SYSTEMS GET WEAKER AND PASS NORTH
OF WRN WA. THE ECMWF SHOWS A WEAK UPPER SHORTWAVE TROUGH MOVING THROUGH
B.C. FRIDAY AND THEN A STRONG RIDGE FOR NEXT WEEKEND WITH A COUPLE OF
RATHER WARM DAYS. THE GFS HAS A FAIRLY STRONG TROUGH MOVING INTO B.C.
ON SAT AND THEN DIGGING SE THRU ALBERTA ON SUNDAY...KEEPING HEIGHTS
LOWER AND COOLER AIR OVER WRN WA. THE TIMING OF TROPICAL MOISTURE KICKING
INTO THE WESTERLIES OUT AROUND 160W PROBABLY ACCOUNTS FOR THE DIFFERENCE
BUT MOST OF THE GFS ENSEMBLE MEMBERS SHOW GRADUALLY WARMING TEMPS ALOFT
FOR THE NEXT WEEK AND A TREND TO WARMER SUNNIER WEATHER IS A GOOD
BET AND THE 18Z GFS ALSO LOOKS WARMER THAN THE PREVIOUS RUN NOW
TOWARD THE END OF NEXT WEEK.

&&

.AVIATION...AN UPPER LEVEL LOW OVER SOUTHWEST WASHINGTON IS MOVING
SLOWLY SOUTH INTO OREGON THIS AFTERNOON. THE FLOW ALOFT IS LIGHT AND
VARIABLE...AND WILL SWITCH TO NORTHERLY AND STRENGTHEN EARLY
SATURDAY BEFORE SWITCHING TO NWLY SATURDAY EVENING. THE AIRMASS IS
BECOMING MOIST AND UNSTABLE...AND BROKEN LOW VFR STRATUS WILL BECOME
MORE SPOTTY AND BE REPLACED WITH HIGHER VFR CIGS FROM REMNANTS OF
THUNDERSTORMS OVER THE CASCADES. I AM NOT EXPECTING THE TSTORMS THIS
EVENING TO MAKE IT FAR ENOUGH WESTWARD TO AFFECT THE TERMINALS. VFR
CONDITIONS SHOULD CONTINUE THROUGH THE REST OF THE PERIOD FOR THE
MOST PART...WITH THE EXCEPTION OF SOME PATCHY FOG OR LOW CLOUDS IN
THE EARLY MORNING HOURS SATURDAY...WITH THE GREATEST CHANCE AT KOLM
AND KHQM.

KSEA...NORTHERLY SURFACE WINDS SHOULD SWITCH TO LIGHT SLY AROUND OR
SOON AFTER MIDNIGHT. SLY WINDS WILL SWITCH TO MORE SWLY AND
STRENGTHEN A BIT SATURDAY EVENING. CHANCES OF EARLY SAT MORNING FOG
OR LOW CLOUDS AFFECTING THE TERMINAL HAVE INCREASED BUT I AM STILL
NOT CONFIDENT ENOUGH TO PUT IN MORE THAN SCT AT SEATAC. JSMITH

&&

.MARINE...SMALL CRAFT ADVISORY LEVEL NORTHERLY WINDS ARE EXPECTED
OVER THE COASTAL WATERS THROUGH THIS EVENING AS ONSHORE GRADIENTS
STRENGTHEN. GRADIENTS WILL SWITCH TO MORE SWLY AND THEN SLY SATURDAY
INTO SUNDAY AS A SURFACE LOW PRESSURE SYSTEM AND ITS ASSOCIATED
FRONT DIP ALONG THE BC COAST AND INTO THE AREA. SMALL CRAFT ADVISORY
LEVEL WINDS WILL OCCUR IN THE STRAIT AHEAD OF THE FRONT LATE
SATURDAY. WEAK TO MODERATE ONSHORE FLOW WILL RESUME LATE SUNDAY
AFTER THE LOW PASSES THROUGH AND CONTINUE THROUGH THE BEGINNING OF
NEXT WEEK. JSMITH

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY COASTAL WATERS AND
     CENTRAL AND EAST STRAIT OF JUAN DE FUCA

&&

$$

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