Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS66 KSEW 242208
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PDT THU JUL 24 2014

.SYNOPSIS...MOIST ONSHORE FLOW WILL CONTINUE TONIGHT AND FRIDAY AS A
WEAK WEATHER SYSTEM MOVES TO THE BRITISH COLUMBIA COAST. THERE COULD
BE SOME LIGHT SHOWERS...ESPECIALLY AT THE COAST...BUT THE WESTERN
WASHINGTON INTERIOR SHOULD BE MOSTLY SUNNY FRIDAY AFTERNOON. HIGH
PRESSURE ALOFT WILL BUILD OVER THE REGION THIS WEEKEND...BRINGING
SUNNY WARM WEATHER THAT SHOULD CONTINUE NEXT WEEK.

&&

.SHORT TERM...WESTERLY FLOW PREVAILS ACROSS WESTERN WASHINGTON THIS
AFTERNOON...AS THE UPPER LOW THAT WE HAVE BEEN DEALING WITH MOVES
ACROSS SOUTHERN ALBERTA. THE AIR MASS IS MOIST TO AROUND 7000 FT
WITH ONSHORE LOW LEVEL FLOW. SPOTTY LIGHT PRECIPITATION CONTINUES
ACROSS THE FORECAST AREA ESPECIALLY OVER THE CASCADES AND THE
CENTRAL PUGET SOUND IN A WEAK CONVERGENCE ZONE. THE REAL SUN BREAKS
HAVE BEEN LIMITED TO THE SOUTH END OF PUGET SOUND AND HOOD CANAL AND
THE NORTHWEST INTERIOR.

WESTERLY FLOW WILL CONTINUE TONIGHT AND FRIDAY. THE AIR MASS WILL
REMAIN MOIST BELOW 7000 FT OR SO TONIGHT. SOME LIGHT SPOTTY SHOWERS
WILL PROBABLY CONTINUE TONIGHT IN THE MOUNTAINS...AT THE COAST...AND
IN THE CONVERGENCE ZONE. RECENT MODEL RUNS ARE DELAYING THE UPPER
RIDGE BUILDING NORTHWARD OVER THE REGION...AND THEY NOW SHOW THE
WEAK SHORTWAVE -- JUST NOW REACHING 130W -- MOVING ONTO THE BRITISH
COLUMBIA COAST FRIDAY AFTERNOON. SO WE ARE REVISING THE FORECAST TO
ADD A CHANCE OF SHOWERS TO THE COAST AND OLYMPICS...BUT STAYING WITH
THE FORECAST THAT SKIES WILL BECOME MOSTLY SUNNY IN THE INTERIOR.

THE UPPER RIDGE WILL START BUILDING FRIDAY NIGHT AND SATURDAY AND
BUILD FURTHER THROUGH SUNDAY...WITH ITS AXIS ALONG OR JUST WEST OF
THE ROCKY MOUNTAINS. THE 500 MB HEIGHTS OVER WESTERN WASHINGTON WILL
CLIMB TO AROUND 5820 METERS ON SATURDAY AND 5850 METERS ON SUNDAY.
ONSHORE FLOW WILL BE WEAK. THERE WILL BE SOME MARINE LAYER CLOUDS AT
NIGHT AND DURING THE MORNING HOURS...ESPECIALLY AT THE COAST...BUT
THE DAYS WILL BE SUNNY AND WARMER.   MCDONNAL

.LONG TERM...THE UPPER RIDGE WILL BE ALONG THE ROCKY MOUNTAINS ON
MONDAY AND IT SHOULD KEEP WESTERN WASHINGTON DRY THROUGH AT LEAST
THURSDAY. SOME RECENT RUNS OF THE LONGER RANGE MODELS -- ESPECIALLY
OF THE ECMWF -- SHOW THE UPPER RIDGE SHIFTING WESTWARDS TOWARD OUR
AREA DURING THE MIDDLE OF THE WEEK...WHICH WOULD RESULT IN WARMER
WEATHER YET. FOR NOW WE CAN EXPECT LIGHT ONSHORE FLOW TO KEEP THE
COAST IN THE UPPER 60S TO 70S...WITH TEMPERATURES IN THE 80S TO
LOWER 90S INLAND.   MCDONNAL

&&

.AVIATION...MODERATE WESTERLY FLOW ALOFT WILL CONTINUE TONIGHT AND
FRIDAY. MODERATE LOW LEVEL ONSHORE FLOW WILL WEAKEN LATER TONIGHT.
AIR MASS IS UNSTABLE AND MOIST THIS AFTERNOON BUT WILL STABILIZE AND
DRY THIS EVENING. A PUGET SOUND CONVERGENCE ZONE EXTENDS WESTWARD
FROM NORTH KING COUNTY. A WEAK WEATHER SYSTEM COULD BRING A LITTLE
RAIN OR DRIZZLE TO THE COAST AND OLYMPICS OVERNIGHT AND FRIDAY.

CEILINGS ARE GENERALLY VFR 4-6K FT EXCEPT FOR MVFR 2-3K FT IN
SHOWERS...WHICH ARE MAINLY IN THE PSCZ. MOST AREAS WILL REMAIN VFR
THIS EVENING...THEN FALL TO MVFR LATE TONIGHT AND FRIDAY MORNING.
GOOD CLEARING IS LIKELY FRIDAY AFTERNOON.

KSEA...PSCZ IS JUST NORTH OF THE TERMINAL. WILL FORECAST KSEA TO
STAY JUST SOUTH OF THE CONVERGENCE...KEEPING GUSTY SOUTHWEST WINDS
THIS EVENING AND CEILINGS RIGHT AROUND 3K FT. FORECAST IS IFFY
ENOUGH THAT THINGS COULD CHANGE BY NEXT TAF ISSUANCE TIME. CHB

&&

.MARINE...MODERATE ONSHORE FLOW HAS DEVELOPED WITH SMALL CRAFT
ADVISORY STRENGTH WINDS OCCURRING IN THE STRAIT. MODELS INDICATE
ONSHORE GRADIENTS WILL DIMINISH THIS EVENING AND THE ADVISORY LEVEL
WINDS SHOULD END BY 06Z.

A MORE TYPICAL ONSHORE FLOW PATTERN WILL PERSIST THROUGH THE WEEKEND
WITH SMALL CRAFT ADVISORY WESTERLIES IN THE STRAIT POSSIBLE AT TIMES
DURING THE AFTERNOON AND EVENING HOURS. FOR NOW HAVE INDICATED SMALL
CRAFT ADVISORY WINDS SATURDAY AND SUNDAY EVENINGS. ELSEWHERE WINDS
SHOULD REMAIN BELOW 20 KT. CHB

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY CENTRAL AND EAST STRAIT.

&&

$$

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




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.