Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 291106 CCA
AFDSEW

AREA FORECAST DISCUSSION...CORRECTED SYNOPSIS
NATIONAL WEATHER SERVICE SEATTLE WA
400 AM PDT WED OCT 29 2014

.SYNOPSIS...HIGH PRESSURE ALOFT WILL MOVE THROUGH THE AREA TODAY FOR
A DRYING TREND. A FRONTAL SYSTEM WILL BRING RAIN THURSDAY AND
THURSDAY NIGHT WITH SHOWERS BEHIND THE FRONT ON FRIDAY. SATURDAY
LOOKS MAINLY DRY IN BETWEEN WEATHER SYSTEMS. WET WEATHER WILL RETURN
SUNDAY AND CONTINUE INTO EARLY NEXT WEEK AS ADDITIONAL FRONTS MOVE
ONSHORE.

&&

.SHORT TERM...SATELLITE IMAGERY AND DOPPLER RADAR SHOW SCATTERED
SHOWERS OVER WESTERN WASHINGTON EARLY THIS MORNING WITH MOST OF THE
SHOWER ACTIVITY ALONG THE COAST AND IN THE MOUNTAINS. TEMPERATURES
AT 3 AM WERE IN THE 50S.

STILL A FEW SHOWERS OFFSHORE TO MOVE THROUGH THE AREA THIS MORNING.
WEAK UPPER LEVEL RIDGE OUT AHEAD OF THE NEXT WEATHER SYSTEM TO REACH
THE AREA MOVING THROUGH WESTERN WASHINGTON LATER THIS MORNING INTO
THIS AFTERNOON. THIS WILL BRING ABOUT AN END TO THE SHOWERS THIS
AFTERNOON. WITH LOW TEMPERATURES MOSTLY IN THE 50S WITH A LITTLE BIT
OF SUNSHINE HIGHS NEAR 60 WILL BE COMMON.

NEXT SYSTEM TO REACH THE AREA CURRENTLY BACK OUT NEAR 139W MOVING
EAST. LARGE DEEP COLD TROUGH BEHIND THE FRONT BETWEEN 140-155W
DIGGING SOUTH. THE TROUGH WILL DIG FAR ENOUGH SOUTH TO TURN THE FLOW
ALOFT OVER WESTERN WASHINGTON SOUTH SOUTHWESTERLY...ENOUGH TO PULL
THE MOISTURE CURRENTLY DOWN NEAR 38N/130-140W UP OVER WESTERN
WASHINGTON AHEAD OF THE FRONT. THIS PROCESS WILL BEGIN LATE
WEDNESDAY NIGHT AND CONTINUE INTO THURSDAY. IN ADDITION TO PULLING
THE MOISTURE UP FOR THE SOUTH...THE DEEPENING TROUGH WILL ALSO SLOW
THE EASTWARD PROGRESS OF THE FRONT DOWN TO A CRAWL ON THURSDAY. END
RESULT THE FORECAST FOR THURSDAY AND THURSDAY NIGHT IS JUST RAIN FOR
THE ENTIRE AREA. WITH THE SOUTH SOUTHWESTERLY FLOW ALOFT THERE WILL
BE A NICE RAIN SHADOW EFFECT ALONG THE EAST PORTION OF THE STRAIT OF
JUAN DE FUCA. HIGHS ONCE AGAIN ON THURSDAY WILL BE NEAR 60 WITH LOWS
OVERNIGHT THURSDAY NIGHT IN THE UPPER 40S TO MID 50S.

FRONT MOVING THROUGH WESTERN WASHINGTON LATE THURSDAY NIGHT/EARLY
FRIDAY MORNING. SATELLITE IMAGERY SHOWS PLENTY OF SHOWER ACTIVITY
BEHIND THE FRONT WHICH WILL MOVE OVER THE AREA ON FRIDAY. THE AIR
MASS WILL COOL AS WELL WITH THE SNOW LEVEL DROPPING DOWN TO NEAR
4500 FEET FRIDAY NIGHT SO A FEW MORE INCHES OF NEW SNOW IS LIKELY AT
PARADISE ON MOUNT RAINIER.

.LONG TERM...UPPER LEVEL TROUGH AXIS MOVING THROUGH WESTERN
WASHINGTON FRIDAY NIGHT. GOOD AGREEMENT IN THE EXTENDED MODELS ON
SATURDAY WITH A WEAK RIDGE MOVING OVER THE AREA RESULTING IN A DRY
DAY FOR MOST LOCATIONS. RIDGE HANGING AROUND INTO SATURDAY NIGHT.
EXTENDED MODELS ARE ALSO IN GOOD AGREEMENT THAT THE NEXT SYSTEM TO
MOVE INTO WESTERN WASHINGTON DROPPING DOWN FROM THE NORTHWEST WILL
BE A LITTLE SLOWER...SO HAVE DRIED OUT THE FORECAST FOR SATURDAY
NIGHT EXCEPT FOR THE COAST. THE SYSTEM ON SUNDAY WILL BE THE FIRST
IN A SERIES OF SYSTEMS THAT WILL KEEP WESTERN WASHINGTON WET THROUGH
AT LEAST THE FIRST HALF OF NEXT WEEK. FELTON

&&

.HYDROLOGY...SHOWERS OVER THE OLYMPICS OVERNIGHT HAVE CAUSED THE
SKOKOMISH TO RISE TO NEAR FLOOD STAGE EARLY THIS MORNING. A SHORT
FUSED FLOOD WARNING MAY BE ISSUED IF THIS TREND CONTINUES FOR THE
NEXT COUPLE OF HOURS. IF THE RIVER REACHES FLOOD STAGE IT WILL NOT
STAY THERE VERY LONG WITH THE DRYING TREND LATER TODAY. MORE
SIGNIFICANT RAIN IN STORE FOR THE SOUTH SLOPES OF THE OLYMPICS
THURSDAY AND THURSDAY NIGHT. IF THE SKOKOMISH DOES NOT GET A CHANCE
TO RECEDE MUCH IN THE NEXT 24 HOURS IT COULD REACH FLOOD STAGE AGAIN
LATE THURSDAY WITH THE NEXT ROUND OF RAINFALL.

FOR THE OTHER RIVERS...FLOODING IS NOT EXPECTED FOR THE NEXT 7 DAYS.
FELTON

&&

.AVIATION...THE WEAK UPPER LEVEL SHORTWAVE TROUGH OVER W WA AT
09Z...EMBEDDED IN W FLOW ALOFT...WILL CONTINUE E AND DISSIPATE THIS
MORNING. RESIDUAL SHOWER ACTIVITY CONTINUES BUT SHOULD GRADUALLY
DIMINISH THIS MORNING AS THE UPPER LEVEL TROUGH DEPARTS AND A WEAK
UPPER LEVEL RIDGE BUILDS OVER THE REGION. THE LOWER AIR MASS REMAINS
MOIST WHICH IS PRODUCING PREDOMINANTLY MVFR CIGS AND LOW END VFR
CIGS BKN030-050. THESE CONDITIONS WILL CONTINUE THROUGH 19Z...BUT AS
THE RIDGE TAKES HOLD...GRADUAL IMPROVEMENT TO SCT-BKN LAYERS 030-050
IS EXPECTED BY 22Z. AN APPROACHING FRONTAL SYSTEM WILL SPREAD RAIN
AND LOWER CONDITIONS ACROSS W WA AFTER 09Z.

KSEA...MOST OF THE SHOWERS CROSSING W WA HAVE BEEN MISSING THE KSEA
AREA...BUT A FEW COULD STILL REACH THE TERMINAL THROUGH 16Z. CIGS
WILL REMAIN BKN-OVC020-040 THROUGH THIS MORNING...BUT SHOULD IMPROVE
TO SCT-BKN040-050 BY 22Z. SURFACE WINDS WILL REMAIN SOUTHERLY
5-10KT. KAM

&&

.MARINE...A WEAK SURFACE RIDGE WILL BUILD OVER W WA TODAY ALLOWING
SURFACE WINDS TO WEAKEN. SWELL ON THE COAST IS STILL ABOVE 10 FEET
THIS MORNING...BUT WILL SUBSIDE BELOW 10 FEET BY THIS EVENING...SO A
SCA FOR HAZARDOUS SEAS WILL REMAIN IN EFFECT TODAY. THE SWELL WILL
KEEP THE GRAYS HARBOR BAR CONDITIONS ROUGH THIS MORNING.

THE NEXT PACIFIC FRONTAL SYSTEM WILL AFFECT WESTERN WA TONIGHT NIGHT
INTO THURSDAY. THE UPPER LEVEL TROUGH CURRENTLY PLOWING E NEAR
45N/140W-150W WILL EVENTUALLY STIMULATE A FRONTAL WAVE ON THE
BAROCLINIC ZONE OFF THE S OREGON COAST...LEFTOVER FROM AN EARLIER
SYSTEM. AS THE SYSTEM DEVELOPS...FALLING PRESSURES OFFSHORE WILL
INCREASE THE E-SE FLOW ACROSS THE AREA. SCA LEVEL WINDS ARE EXPECTED
OVER THE COASTAL WATERS AND WEST ENTRANCE TONIGHT AND OVER SOME OF
THE NORTHERN INTERIOR WATERS THURSDAY. THERE IS SOME CONCERN
REGARDING E FLOW THROUGH THE W ENTRANCE TO THE STRAIT. THE GFS SHOWS
ABOUT A 4.5 MB PRESSURE UIL-BLI PRESSURE GRADIENT 12Z/18Z
THURSDAY...BUT THE COARSER GFS FREQUENTLY OVER-FORECASTS THE
GRADIENT. BUT WITH THE NAM AND ECMWF BOTH SHOWING 3-3.5 MB
GRADIENTS...WHICH PUTS IT IN THE RANGE FOR A POTENTIAL
GALE...CONFIDENCE IS HIGH ENOUGH TO ISSUE A GALE WATCH.

A WEAK SURFACE RIDGE WILL REFORM OVER THE REGION FRIDAY AND
SATURDAY. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...

WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS COAST AND WEST
      ENTRANCE.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.
     GALE WATCH FOR THE WEST ENTRANCE.

&&

$$

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













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