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National Weather Service meteorologists use a wide variety of tools such as observations,
satellite imagery, radar imagery, and computer models to aid in making forecasts. The Enhanced
Area Forecast Discussion is intended to provide additional insight into our traditional Area
Forecast Discussion (AFD) by including embedded links to some of the key tools used in the
forecast process. These links are specific to the forecast issue of the day and are updated as the
forecast discussion is updated.
For comments or feedback please
contact the Seattle WFO
Webmaster
For more information on the terms used in the Enhanced AFD, please see
Frequently Asked Questions (updated 20 May, 2008).
For help decoding the image legends, please see
Legends Help.
Previous Version
ZCZC SEAGPHAFD 000
TTAA00 KSEA 062231
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
245 PM PDT WED MAY 6 2009
.SYNOPSIS...SHOWERS WILL CONTINUE TONIGHT AND THURSDAY MORNING...
THEN DIMINISH THURSDAY AFTERNOON AND NIGHT AS AN UPPER TROUGH MOVES
EAST AND A WEAK UPPER LEVEL RIDGE BUILDS. THE UPPER LEVEL RIDGE WILL
KEEP THE AREA DRY WITH MORE SUNSHINE FRIDAY THROUGH SUNDAY...BUT
ONSHORE FLOW WILL KEEP TEMPERATURES CLOSE TO NORMAL. AN UPPER LEVEL
TROUGH MAY BRING SHOWERS EARLY NEXT WEEK.
&&
.SHORT TERM...WIND SWITCHED FROM EASTERLY TO SOUTHWESTERLY ON THE
COAST 20Z-21Z AND RAIN HAS BECOME LIGHTER AND MORE SHOWERY THERE.
MEANWHILE THE RAIN AROUND PUGET SOUND WAS HEAVIEST DURING THIS TIME.
SATELLITE IMAGERY AND RADAR (image) ARE BOTH SHOWING FRONTAL
SIGNATURES. UPSHOT IS THERE SHOULD BE A FRONTAL PASSAGE THROUGH
PUGET SOUND 22Z-00Z AND RAIN SHOULD BECOME MORE SHOWERY THEN. THERE
WILL BE A BURST OF SOUTHWEST WINDS 10-20 MPH WITH SOME HIGHER GUSTS
FOR A FEW HOURS AROUND FRONTAL PASSAGE.
SKIES WILL BE MOSTLY CLOUDY TONIGHT AND SHOWERS REMAIN LIKELY. THERE
WILL BE SOME BREAKS IN THE CLOUDS AND SHOWERS SHOULD TAPER AS THE
NIGHT GOES ON. A BROAD UPPER TROUGH WILL CROSS THE AREA TONIGHT...IT
WILL BE CENTERED OVER WESTERN WASHINGTON AROUND 12Z AND WILL BE OVER
EASTERN WASHINGTON BY 18Z. THIS MEANS SHOWERS WILL DIMINISH DURING
THE DAY ON THURSDAY...ESPECIALLY IN THE AFTERNOON. THERE ALSO SHOULD
BE SOME SUN BY THURSDAY AFTERNOON AND TEMPERATURES WILL BE A FEW TO
SEVERAL DEGREES WARMER THAN TODAY...MAINLY 55 TO 60.
ON THURSDAY NIGHT HEIGHTS BUILD AND SURFACE PRESSURE BUILDS
OFFSHORE. THIS WILL END SHOWERS AND SKIES WILL CLEAR SIGNIFICANTLY.
THERE MAY STILL BE SOME CLOUDS AROUND FRIDAY MORNING BUT THEY SHOULD
CLEAR DURING THE DAY AND TEMPERATURES SHOULD CLIMB INTO THE 60S. A
FEW MOUNTAIN SHOWERS ARE STILL POSSIBLE (image). THIS PATTERN HOLDS
THROUGH SATURDAY...WITH TEMPERATURES A FEW DEGREES HIGHER. ONSHORE
SURFACE FLOW EACH DAY SHOULD PREVENT TEMPERATURES FROM GETTING MUCH
HIGHER...THOUGH A STRAY 70 COULD OCCUR IN THE FAR SOUTHWEST
INTERIOR. BURKE
.LONG TERM...SUNDAY IS LIKELY TO BE SIMILAR TO SATURDAY. LATEST
MODELS HOLD OFF THE NEXT SYSTEM UNTIL SUNDAY NIGHT. PREVIOUS MODEL
RUNS WERE FASTER...AND ANYWAY HIGH CLOUDS COULD INCREASE IN THE
AFTERNOON. HAVE CALLED IT PARTLY CLOUDY DUE TO SOME UNCERTAINTY.
BOTH THE GFS AND EURO CALL FOR A CHANGE IN THE PATTERN NEXT WEEK.
THEY DIFFER ON THE DETAILS WITH THE GFS BRINGING A LOW ACROSS
SOUTHERN WASHINGTON ABOUT TUESDAY AND THE EURO SWINGING IT INLAND
WELL NORTH OF WASHINGTON WITH A TRAILING FRONT (image). EITHER WAY
THERE IS A CHANCE OF SOME RAIN EACH DAY AND HAVE PLAYED IT AS A
MOSTLY CLOUDY PERIOD WITH A CHANCE OF SHOWERS...KIND OF A BROAD
BRUSH. BURKE
&&
AVIATION...BACK EDGE OF FRONTAL SYSTEM APPROACHING COAST NEAR KHQM
AT 21Z...WITH MVFR CONDITIONS IN -RA BR CONTINUING OVER W WA.(image)
EXPECT FRONT TO CONTINUE GRADUAL E-NE MOVEMENT WITH MVFR CONDITIONS
BREAKING UP A LITTLE AS FRONTAL BAND CROSSES THE AREA. AFTERNOON
SATELLITE PHOTOS DEPICT LOTS OF SHOWER ACTIVITY OFFSHORE TO WORK
THROUGH OVERNIGHT.(image) GUSTY SW WINDS STILL EXPECTED THIS EVENING
INTO LATE TONIGHT AS COLD FRONT MOVES INTO THE CASCADES. A
COOL...MOIST AND UNSTABLE AIR MASS REMAINS OVER W WA THURSDAY FOR
THE CONTINUED THREAT OF SHOWERS.(image) PRANGE
KSEA...MVFR CONDITIONS WITH -RA BR AND GUSTY S WINDS TO CONTINUE TIL
LATE THIS EVENING...06-07Z. THEN CIGS EXPECTED TO GRADUALLY RISE AND
WINDS EASE OVERNIGHT. EXPECT POSSIBLE MVFR CONDITIONS THURSDAY WITH
SHOWER THREAT. PRANGE
&&
.MARINE...SMALL CRAFT ADVISORY LEVEL WINDS REMAIN UP ALL AREAS
THROUGH LATE TONIGHT COAST AND ENTRANCES AND THROUGH MIDNIGHT
ELSEWHERE. WINDS EASE SOME EARLY THURSDAY...THEN PICK UP AGAIN IN
THE STRAIT AND NORTHERN WATERS THURSDAY AFTERNOON AND EVENING...AS
THE UPPER LEVEL TROUGH MOVES EAST AND PRESSURE GRADIENTS
INCREASE.(image) PRANGE
&&
.AVALANCHE...A HIGH BACK COUNTRY AVALANCHE DANGER IS EXPECTED AT
HIGHER ELEVATIONS IN THE OLYMPICS...WASHINGTON CASCADES AND MT HOOD
AREA LATE THIS WEEK AND THIS WEEKEND. A SPECIAL AVALANCHE STATEMENT
HAS BEEN ISSUED VIA THE NWAC AVALANCHE FORECAST PRODUCTS. THE
STATEMENT WILL BE UPDATED AS CONDITIONS WARRANT. PLEASE VISIT
WWW.NWAC.US FOR DETAILS. FERBER
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...
PZ....SMALL CRAFT ADVISORY ALL WATERS THROUGH LATE THIS EVENING.
.SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.
$$
WWW.WEATHER.GOV/SEATTLE
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