Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 010955
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
255 AM PDT SAT NOV 1 2014

.SYNOPSIS...A WEAK UPPER LEVEL TROUGH WILL MOVE ACROSS WESTERN
WASHINGTON TODAY FOR MAINLY DRY WEATHER WITH A LITTLE SUNSHINE
SATURDAY. A WEAK RIDGE WILL FOLLOW TONIGHT EXTENDING THE DRY PERIOD
A LITTLE LONGER. A WARM FRONT WILL BRING A LITTLE RAIN SUNDAY AND
SUNDAY NIGHT. A STRONGER WARM FRONT WILL BRING MORE EXTENSIVE RAIN
AND LOCALLY WINDY WEATHER MONDAY AND TUESDAY. THE ACTIVE WET WEATHER
PATTERN WILL LIKELY CONTINUE THE REST OF NEXT WEEK.

&&

.SHORT TERM...AN ELONGATED WEAK UPPER LEVEL TROUGH WAS JUST OFFSHORE
THIS MORNING...EXTENDING FROM THE WA WATERS DOWN TO CENTRAL CA.
SHOWERS WERE NON-EXISTENT OVER W WA THIS MORNING AND WERE ONLY
ISOLATED OFFSHORE. THE TROUGH WILL MOVE INLAND ACROSS W WA TODAY BUT
WILL HAVE LITTLE EFFECT. I WILL HANG ON TO THE SLIGHT CHANCE OF
SHOWERS FOR THE COAST AND MOUNTAINS TODAY AND TONIGHT.

NAM HI-RES SOUNDINGS INDICATE THE LOWER AIR MASS WILL BECOME WEAKLY
UNSTABLE TODAY...BUT THIS LITTLE BIT OF LIFT WILL PROBABLY RESULT IN
JUST A BIT MORE CLOUD COVER THIS AFTERNOON. OVERALL THOUGH THERE
SHOULD BE ENOUGH SUNSHINE TO CALL IT PARTLY SUNNY.

THE UPPER LEVEL TROUGH WILL SLIDE EAST TONIGHT ALLOWING A WEAK UPPER
LEVEL RIDGE TO MOVE ACROSS W WA. NO BIG IMPACT IS EXPECTED EXCEPT
THE CLOUD COVER UNDER THE RIDGE OUT BETWEEN 130W-140W WILL MOVE
INLAND.

MODELS SHOW A WET PERIOD COMING UP THIS WEEK...STARTING ON SUNDAY.
IR/WATER VAPOR IMAGERY SHOWS SOME TROPICAL MOISTURE BEING PUMPED
NORTHWARD INTO THE WESTERLIES AROUND THE DATELINE...WHICH WILL
PROBABLY END UP BEING THE RAINY PERIOD MONDAY AND TUESDAY.

MODELS ARE IN FAIR AGREEMENT WITH THE DETAILS SUNDAY THROUGH
TUESDAY. THE INITIAL WARM FRONT SPREADS SOME LIGHT RAIN TO THE COAST
SUNDAY MORNING...WITH A LITTLE RAIN REACHING PUGET SOUND IN THE
AFTERNOON. THE WEAK WARM FRONT WILL GO THROUGH SUNDAY NIGHT LEAVING
UP TO A QUARTER INCH OVER THE INTERIOR AND 0.25-0.50 ON THE COAST.

AFTER HARDLY MUCH BREAK AT ALL THE TRAILING STRONGER WARM FRONT WILL
AFFECT THE AREA MONDAY THROUGH TUESDAY...WITH THE HEAVIEST RAIN
MONDAY NIGHT THROUGH TUESDAY MORNING. SHOULD BE WINDY COAST AND N
INTERIOR AS WELL. 36 HOUR RAIN ACCUMULATIONS MONDAY MORNING THROUGH
TUESDAY AFTERNOON MAY EXCEED AN INCH OVER THE INTERIOR LOWLANDS
WITH DOUBLE THAT ON THE COAST. THE SOUTHERN OLYMPICS COULD PICK
UP 3-4 INCHES. THE WARM ADVECTION WILL PUSH LOWS UP INTO THE LOWER
50S WITH HIGHS IN THE MID TO UPPER 50S. KAM

.LONG TERM...GFS AND ECMWF AGREE ON PUSHING ANOTHER WARM FRONT
NORTHWARD ACROSS THE AREA TUESDAY NIGHT AND WEDNESDAY MORNING. THIS
DOES NOT LOOK LIKE AND OVERLY WET FEATURE. BOTH MODELS ALSO INDICATE
A LULL IN THE RAIN STARTING WEDNESDAY AFTERNOON OR SO...BUT DISAGREE
ON JUST HOW LONG THE LULL WILL BE. ECMWF BRINGS THE NEXT SYSTEM TO
THE AREA THURSDAY AFTERNOON WHILE THE GFS HOLDS OFF UNTIL THURSDAY
NIGHT. OTHER DETAILS AFFECTING QPF AND WIND DIFFER AS WELL. KAM

&&

.HYDROLOGY...A COUPLE OF WARM FRONTS WILL BRING AROUND 2 TO 4 INCHES
OF RAIN...AND LOCALLY PERHAPS 5 INCHES...TO THE OLYMPIC MOUNTAINS
SUNDAY NIGHT THROUGH TUESDAY...WITH THE HIGHEST TOTALS OVER THE
SOUTHERN OLYMPICS. FLOODING IS POSSIBLE ON THE EXCEPTIONALLY
FLOOD-PRONE SKOKOMISH RIVER IF THAT OCCURS.

FLOODING IS UNLIKELY ON ALL OTHER RIVERS IN OUR FORECAST AREA FOR
THE NEXT 7 DAYS.

IN ADDITION...RECENT HEAVY PRECIPITATION AMOUNTS HAVE CREATED
ANTECEDENT CONDITIONS FAVORABLE TO LANDSLIDES IN WESTERN
WASHINGTON...ACCORDING TO THE USGS LANDSLIDE HAZARDS PROGRAM. IN
FACT...PRECIPITATION FOR THE MONTH OF OCTOBER AT SEATAC IS AROUND
190 PERCENT OF NORMAL...AND THIS WILL PROBABLY BE THE FOURTH WETTEST
OCTOBER ON RECORD AT SEATAC. THE THREAT OF LANDSLIDES WILL BE
SOMETHING TO WATCH AS A WET WEATHER PATTERN CONTINUES. MCDONNAL/KAM

&&

.AVIATION...SW FLOW ALOFT WILL BECOME NW TODAY AS A WEAK UPPER
TROUGH MOVES ACROSS THE AREA. LIGHT OFFSHORE FLOW SHOULD TURN
ONSHORE. AREAS OF LOW CLOUDS AND FOG ARE LIKELY THIS MORNING...THE
AFTERNOON WILL LIKELY SEE PARTLY SUNNY SKIES...AND THEN CLOUDS
SHOULD RETURN TONIGHT. THE TIME HEIGHT CROSS SECTION FOR SEATTLE
SHOWS A LOT OF LOW LEVEL MOISTURE...INCREASING TONIGHT.


KSEA...LOW LEVEL MOISTURE MIGHT BE PESKY TODAY AND LOW LEVEL
MOISTURE WILL INCREASE AGAIN TONIGHT SO DESPITE THE BREAK BETWEEN
WEATHER SYSTEMS TODAY WE MAY SEE MORE CLOUDS THAN SUN.

&&

.MARINE...PRESSURE GRADIENTS WILL BE LIGHT TODAY. A WARM FRONT WILL
BRUSH THE AREA SUNDAY WITH SOUTHERLY FLOW INCREASING. A STRONG
FRONT WILL REACH THE AREA LATER ON MONDAY. LOADING THE UW WRFGFS
WINDS INTO THE GRIDS/FORECAST MAKES GALES LOOK LIKE A GOOD
POSSIBILITY MONDAY NIGHT COASTAL WATERS AND PERHAPS THE NORTHERN
WATERS.


&&

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

&&

$$

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








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