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 162141
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
242 PM PDT THU APR 16 2015

.SYNOPSIS...AN UPPER LEVEL RIDGE WILL KEEP SKIES MOSTLY CLEAR
TONIGHT WITH COOL TEMPERATURES. A WEAK DRY UPPER LEVEL TROUGH WILL
BRING PERIODS OF CLOUDS TO WESTERN WASHINGTON ON FRIDAY. A STRONGER
UPPER LEVEL RIDGE WILL BRING MOSTLY SUNNY AND WARMER WEATHER
SATURDAY THROUGH TUESDAY. A LARGE UPPER LEVEL TROUGH WILL BRING
SHOWERS TO THE AREA TUESDAY NIGHT THROUGH THURSDAY.

&&

.SHORT TERM...THE LOW AMPLITUDE UPPER LEVEL RIDGE OVER W WA THIS
AFTERNOON WILL SLIDE E TONIGHT AS THE UPPER LEVEL SHORTWAVE TROUGH
OFFSHORE NEAR 45N/140W APPROACHES. THE AIR MASS IS DRY AND GOOD
RADIATIONAL COOLING TONIGHT MAY ALLOW THE COLDEST SPOTS TO REACH THE
MID TO UPPER 30S AGAIN FRIDAY MORNING.

THE UPPER LEVEL SHORTWAVE TROUGH OFFSHORE NEAR 45N/140W AT 20Z WILL
TRACK ACROSS THE AREA ON FRIDAY. MODELS HAVE CONTINUED TO KEEP THIS
FEATURE WEAK AND JUST ABOUT COMPLETELY DRY...SO ANY MENTION OF
SHOWERS HAS BEEN DROPPED FROM THE FORECAST. THE SKINNY REMNANTS OF
THE FRONTAL BAND WILL CROSS W WA DURING THE DAY...BUT CLOUD COVER
SHOULD BE MINIMAL ENOUGH TO MAINTAIN A MOSTLY SUNNY FORECAST.

THE APPROACHING TROUGH WILL PUSH AN AREA OF STRATUS OVER THE COASTAL
WATERS ON FRIDAY AS IT MOVES INLAND. MODERATE LOW LEVEL ONSHORE FLOW
WILL DEVELOP BEHIND THE SHORTWAVE TROUGH FRIDAY AFTERNOON AND
EVENING WHICH WILL SPREAD THE MOIST COASTAL AIR MASS INLAND. THE
06Z/12Z NAM IS NOW INDICATING MORE OF A NW PUSH WITH THE COASTAL
STRATUS...SO LESS LOW LEVEL MOISTURE SHOULD REACH THE PUGET SOUND
REGION. AT THIS POINT IT LOOKS LIKE THE COAST...STRAIT...AND SW
INTERIOR WILL SEE THE MOST STRATUS...WITH JUST PATCHY STRATUS OVER
PUGET SOUND. OF COURSE THERE IS STILL QUITE A BIT OF UNCERTAINTY
REGARDING THE LOW CLOUD COVERAGE. STRATUS OVER THE INTERIOR SHOULD
CLEAR RAPIDLY BEFORE SATURDAY AFTERNOON...WITH SUNNY SKIES AND
AFTERNOON MAX TEMPS IN THE 60S. STRATUS ON THE COAST SHOULD CLEAR
FROM THE N AS DRIER AIR MOVES IN.

A STRONGER UPPER LEVEL RIDGE WILL BUILD OFFSHORE ALONG 130W ON
SATURDAY...BEHIND THE DEPARTING TROUGH...THEN DOMINATE WEATHER
PATTERN THROUGH TUESDAY. THE AIR MASS WILL REMAIN DRY ON SUNDAY AND
GRADUAL WARMING SHOULD PRODUCE MAX TEMPS IN THE 60S TO LOWER 70S. KAM

.LONG TERM...THE UPPER LEVEL RIDGE AXIS WILL MOVE OVER THE COAST
SUNDAY NIGHT...THEN SHIFT SLOWLY E OVER E WA ON TUESDAY. WEAK LOW
LEVEL OFFSHORE FLOW WILL PUT MAX TEMPS IN THE 60S TO MID 70S MONDAY
AND TUESDAY.

THE GFS...ECMWF...AND CANADIAN CONTINUE TO BE A BIT OF AN
INCONSISTENT MESS FROM TUESDAY NIGHT ONWARD. THERE IS BROAD
AGREEMENT THAT THE UPPER LEVEL RIDGE WILL DRIFT E AND A LARGE UPPER
LEVEL TROUGH WILL APPROACH THE COAST. MOIST S FLOW WILL DEVELOP OVER
W WA AHEAD OF THE TROUGH FOR SOME SHOWERS...BUT JUST WHEN THIS WILL
WILL OCCUR AND HOW IT WILL UNFOLD IS STILL IN DOUBT. SO FOR
NOW...THE TUESDAY NIGHT THROUGH THURSDAY PERIOD HAS A BROADBRUSH
CHANCE OF SHOWERS. KAM

&&

.AVIATION...FLOW ALOFT IS WESTERLY AS A FLAT UPPER LEVEL RIDGE
REMAINS OVER THE PACIFIC NORTHWEST. ON FRIDAY A WEAK UPPER TROUGH
WILL MOVE THROUGH SOUTHERN BRITISH COLUMBIA. AIR MASS IS DRY AND
STABLE. AT THE SURFACE HIGH PRES OFFSHORE WILL GIVE WEAK ONSHORE
FLOW THIS EVENING. VFR CONDITIONS WILL CONTINUE.

KSEA...VFR CONDITIONS WITH ONLY SOME THIN HIGH CLOUDS AT TIMES.
NORTHERLY WIND 8-12 KT WILL EASE OVERNIGHT. CHB

&&

.MARINE...HIGH PRESSURE OVER WESTERN WA WILL BRING GENERALLY LIGHT
NORTHERLY WINDS TONIGHT. WESTERLY SWELLS OF 10 FT OR SO WILL REACH
THE COAST TONIGHT AND A SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS IS
IN EFFECT FOR THE COAST AND WESTERN STRAIT.

ONSHORE FLOW WILL INCREASE ON FRIDAY AS A WEAK TROUGH CROSSES THE
AREA. SMALL CRAFT ADVISORY WINDS ARE LIKELY FOR THE COASTAL WATERS
AND THE STRAIT OF JUAN DE FUCA LATE FRIDAY AFTERNOON AND EVENING.
GALES ARE POSSIBLE IN THE STRAIT AND A GALE WATCH IS IN EFFECT FOR
FRIDAY AFTERNOON AND EVENING. NORTHERLY FLOW WILL DEVELOP SATURDAY
AND SUNDAY AS LOW PRES FORMS ALONG THE COAST. ONSHORE FLOW WILL
RETURN TUESDAY. CHB

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY COAST AND WEST ENTRANCE FOR HAZARDOUS SEAS.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.
     GALE WATCH FRIDAY EVENING 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.