Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 300403
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
ISSUED BY NATIONAL WEATHER SERVICE PORTLAND OR
903 PM PDT MON JUN 29 2015

.SYNOPSIS...SOUTHWESTERLY FLOW CONTINUES AS AN UPPER TROUGH SLOWLY
MOVES NORTHEAST ACROSS THE REGION. ANOTHER UPPER LEVEL TROUGH WILL
PASS BY TO THE NORTH OF THE REGION ON TUESDAY ENHANCING ONSHORE
FLOW. HIGH PRESSURE ALOFT WILL REBUILD OVER THE PACIFIC NORTHWEST ON
WEDNESDAY FOR A RETURN TO HOT AND DRY CONDITIONS REMAINING INTO THE
HOLIDAY WEEKEND.

&&

.UPDATE...OVERALL THE FORECAST SEEMS ON TRACK THIS EVENING. SEEING
EVIDENCE OF A MARINE PUSH ONSHORE AND THE 12Z KUIL UPPER AIR DATA
REFLECTS TOPS AROUND 1600 FT. EXPECT THE MARINE INTRUSION TO
PROGRESS INTO THE LOWER CHEHALIS VALLEY AND INTO THE SOUTH SOUND.
LIKELY SEE MARINE CLOUDS INTO SEATAC AREA AND LINGERING AROUND
DAYBREAK TUESDAY. THESE MARINE CLOUDS AND FOG SHOULD CRAWL INLAND
AND THROUGH THE STRAIT...BUT NOT COMPLETELY BLANKET THE INTERIOR
AREAS IN THE MORNING. GUSTY WINDS LIKELY CONTINUE IN THE CENTRAL AND
EASTERN STRAIT OF JUAN DE FUCA THIS EVENING.

.SHORT TERM /PREVIOUS DISCUSSION/...SOUTHWESTERLY FLOW ALOFT IS
BECOMING MORE WESTERLY THIS AFTERNOON AS AN UPPER LEVEL TROUGH IS
SLOWLY MEANDERING ONSHORE PER SATELLITE IMAGERY. LATEST VISIBLE
SATELLITE IMAGES DEPICT GENERAL CLEARING OVER THE INTERIOR PORTIONS
OF THE FORECAST AREA...WITH STRATUS REMAINING IN GRAYS HARBOR COUNTY
AND CUMULUS DEVELOPMENT OVER THE OLYMPICS AND CASCADES.  TWO
CLUSTERS OF THUNDERSTORMS OVER THE OFFSHORE AND COASTAL WATERS
EARLIER TODAY CONTINUE TO DEPICT LESS IMPRESSIVE RADAR RETURNS ALONG
WITH A SHARP DECREASE IN DETECTED LIGHTNING. WHILE A FEW SHOWERS ARE
NOW REACHING THE COAST NEAR NEAH BAY...LITTLE TO NO QPF IS
ANTICIPATED. DID INCREASE POPS JUST A LITTLE ALONG THE CASCADES TO
ACCOUNT FOR SOME POTENTIAL FOR A SHOWER OR THUNDERSTORM ALONG THE
CASCADES IN THE NEXT FEW HOURS...WITH SOME DECENT INSTABILITY
PRESENT IN THE MODELS. HOWEVER...SEEMS TO BE ENOUGH OF A CAP TO KEEP
THINGS GOING INTO THE EVENING EXCEPT POSSIBLY IN THE NORTH.
INTRODUCED SLIGHT CHANCE THUNDER FOR THE NORTH WASHINGTON CASCADES
THROUGH 06Z...BUT THE SLOWING MOTION OF THE UPPER TROUGH SEEMS TO
PRECLUDE THIS CAPE FROM BEING ACTUALIZED ELSEWHERE.

FORECAST MODELS IN REASONABLY GOOD AGREEMENT WITH RESPECT TO ANOTHER
SHORTWAVE TROUGH SLIDING INLAND WELL TO THE THE NORTH OF THE AREA
LATE TONIGHT INTO TUESDAY...BRINGING INCREASED ONSHORE FLOW. THIS
WILL RESULT IN SLIGHTLY COOLER TEMPERATURES FOR TUESDAY AND A PUSH
OF MARINE STRATUS INTO THE COASTAL ZONES AND INLAND TO PERHAPS
SEATTLE AND THE CENTRAL STRAIT OF JUAN DE FUCA EARLY TUESDAY MORNING.

HIGH PRESSURE ALOFT REBUILDS OFFSHORE BY WEDNESDAY FOR RELAXING LOW
LEVEL ONSHORE. WITH 500 MB HEIGHTS REBOUNDING TO NEAR 5900
METERS...WILL SEE HIGH TEMPERATURES WEDNESDAY AFTERNOON INTO THE 80S
FOR THE INTERIOR. THURSDAY LIKELY EVEN WARMER WITH TEMPERATURES BACK
TO THE 90S...LIKELY THE WARMEST DAY OF THIS WEEK.

.LONG TERM...NO CHANGES. PREVIOUS DISCUSSION FOLLOWS. FORECAST
MODELS REMAIN IN GENERAL AGREEMENT THAT THE UPPER LEVEL RIDGE WEAKEN
SLIGHTLY WITH A FEW UPPER LEVEL SHORTWAVES PASSING WELL TO THE NORTH
OF THE AREA. LOW LEVEL FLOW NEVER APPEARS TO TURN FULLY OFFSHORE AND
WITH HEIGHTS LOWERING A BIT...THINK TEMPERATURES INLAND WILL LIKELY
COOL A BIT BUT REMAIN WELL ABOVE SEASONAL NORMALS WITH WIDESPREAD
80S OVER THE INTERIOR AND 70S FOR THE COAST.  CULLEN

&&

.AVIATION...UNSTABLE S FLOW ALOFT WILL CONTINUE OVER W WA TONIGHT
AS A WEAK UPPER LEVEL SHORTWAVE TROUGH JUST W OF THE OREGON COAST
MOVES NE OVER S B.C. BY 03Z. MORE STABLE SW FLOW ALOFT WILL DEVELOP
IMMEDIATELY BEHIND THE SHORTWAVE TROUGH LATER THIS AFTERNOON...THEN
SHIFT TO W TONIGHT AND TUESDAY.

LOW LEVEL ONSHORE FLOW WILL RETURN AGAIN TONIGHT ALLOWING MVFR/IFR
STRATUS TO PUSH FARTHER INLAND OVER PUGET SOUND LATE TONIGHT. THE
STRATUS SHOULD BURN OFF BY 19Z TUESDAY.

KSEA...GOOD VFR CONDITIONS ARE EXPECTED THIS EVENING. SURFACE WINDS
WILL REMAIN SW 5-12 KT THROUGH 06Z. MVFR/IFR STRATUS WILL PROBABLY
REACH THE TERMINAL AROUND 14Z TUESDAY MORNING.

&&

.MARINE...A WEAK SURFACE LOW OFF THE WASHINGTON COAST ASSOCIATED
WITH AN UPPER LEVEL DISTURBANCE WILL WEAKEN AND SHIFT INLAND
TONIGHT. THIS WILL RESULT IN WINDS SHIFTING TO NORTHWEST ALONG LATE
TONIGHT AND TUESDAY. THERMAL LOW PRESSURE INLAND AND HIGH PRESSURE
BUILDING IN FROM THE WEST WILL RESULT IN GOOD WESTERLY WINDS
THROUGHOUT THE STRAIGHT OF JUAN DE FUCA DURING THE AFTERNOON AND
EVENING HOURS THIS EVENING AND AGAIN TOMORROW AFTERNOON AND EVENING.
THE CANADIAN MODEL INDICATES POSSIBLE GALES IN THE CENTRAL AND
EASTERN STRAIT LATE TUE AFTERNOON AND TUESDAY EVENING...WHILE THE
NAM AND GFS ARE NOT AS STRONG. FOR NOW HAVE KEPT WINDS JUST BELOW
GALE.

AS HIGH PRESSURE BUILDS OFFSHORE THE GRADIENTS OVER THE OUTER WATERS
INCREASE TOMORROW EVENING THROUGH WEDNESDAY WITH SMALL CRAFT WINDS
LIKELY. WS


&&

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

PZ...SMALL CRAFT ADVISORY IN EFFECT FOR THE CENTRAL AND EAST STRAIT
OF JUAN DE FUCA THIS AFTERNOON AND TONIGHT

&&

$$

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


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