Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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 011618
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT WED OCT 1 2014

.SYNOPSIS...NORTHWEST FLOW ALOFT AHEAD OF AN APPROACHING OFFSHORE
RIDGE WILL KEEP WESTERN WASHINGTON MAINLY DRY TODAY THROUGH
FRIDAY...WITH SOMEWHAT SUNNIER AND WARMER WEATHER EACH DAY. A WEAK
FRONT COULD BRING SOME RAIN FRIDAY NIGHT THROUGH EARLY NEXT WEEK...
BUT IT WILL BE A PERIOD OF MILD WEATHER OVERALL AND ANY RAIN THAT
DOES FALL SHOULD BE LIGHT.

&&

.SHORT TERM...OBS AND VISIBLE SATELLITE SHOW AREAS OF STRATUS ACROSS
THE AREA BUT MORE SOLID ACROSS THE N INTERIOR. MODELS INCLUDING THE
NAM-12 AND MOS GUIDANCE ARE SURPRISINGLY PESSIMISTIC ON STRATUS
BREAK OUT TODAY. THE GFS MOS DOES INDICATE SOME CLEARING DURING THE
AFTERNOON WHICH MAKES SENSE GIVEN THE WEAKER FLOW. TEMPERATURES
SHOULD ALSO BE AT LEAST AS WARM AS YESTERDAY AND MOS WAS WAY TOO
COOL. THE CURRENT FORECAST INDICATING PARTY SUNNY SKIES THIS
AFTERNOON AND HIGHS IN THE MID TO UPPER 60S LOOKS ON TRACK.

A WEAK SHORT WAVE ALOFT WILL BRUSH THE AREA LATE TODAY AND TONIGHT.
THE ONLY REAL EFFECT WILL BE INCREASE THE LOW LEVEL ONSHORE FLOW A
BIT. THE NAM-12 SHOWS STRATUS AROUND THE AREA AGAIN THURSDAY MORNING
BUT I SUSPECT THE S SOUND/SW INTERIOR/LOWER CHEHALIS WILL GET MORE
FOG THAN LOW CLOUDS. LOW CLOUDS AND FOG SHOULD LIFT DURING THE
AFTERNOON WITH ANOTHER PARTY SUNNY AFTERNOON ON TAP. HIGHS MAY NOT
NOT WARM MUCH OVER TODAY GIVEN THE BRUSH BY SYSTEM AND ONSHORE
FLOW...SO EXPECT MORE 60S ACROSS WRN WA.

HIGH PRESSURE ALOFT BUILDS LATE THURSDAY INTO FRIDAY. LOW LEVEL NLY
FLOW WILL HELP CLEAR OUT MUCH OF THE RESIDUAL MOISTURE BUT RADIATIVE
COOLING WILL LEAD TO MORE FOG. SOME AREAS AROUND THE S SOUND/SW
INTERIOR COULD HAVE FOG LINGER INTO THE EARLY AFTERNOON. FOG WILL
MIX OUT AND SOME MID/HIGH CLOUDS WILL DRIFT ACROSS THE AREA AS A
WARM FRONTAL SYSTEM PUSHES INTO BRITISH COLUMBIA. MODELS ARE STILL
HAVING TROUBLE RESOLVING THE FRIDAY NIGHT AND BEYOND PERIOD. THE 00Z
GFS/ECMWF BOTH BRING SOME LIGHT QPF TO NRN PORTIONS OF THE
FORECAST AREA FRIDAY NIGHT. WILL NEED TO WAIT FOR ALL THE 12Z
MODELS TO ARRIVE BEFORE ANY ADJUSTMENTS ARE MADE TO THE EXTENDED.
MERCER

.LONG TERM...NO CHANGES FROM PREVIOUS DISCUSSION...THE UPPER RIDGE
WILL WEAKEN AND PROBABLY SHIFT EASTWARD FRIDAY NIGHT AND
SATURDAY...ALLOWING THE FRONTAL SYSTEM IMMEDIATELY UPSTREAM OF THE
RIDGE AXIS TO SAG INTO WESTERN WASHINGTON. DURING THE LAST COUPLE OF
RUN CYCLES...THE MODELS HAVE TRENDED TOWARD DRIER SOLUTIONS FOR
SATURDAY NIGHT THROUGH AT LEAST MONDAY. IN GENERAL THEY ARE KEEPING
THE UPPER RIDGE OVER THE PACIFIC NORTHWEST. THERE IS STILL SOME
UNCERTAINTY WITH REGARD TO THE THREAT OF RAIN BUT THIS SHOULD BE A
PERIOD OF MILD WEATHER OVERALL -- ANY PRECIPITATION THAT DOES OCCUR
SHOULD BE LIGHT AND HIGHS WILL BE IN THE MID 60S TO LOWER 70S.
MCDONNAL

&&

.AVIATION...MODERATE NW FLOW ALOFT WILL CONTINUE OVER W WA BEYOND
12Z THURSDAY. A WEAK UPPER LEVEL SHORTWAVE RIDGE OVER E WA AT 16Z
WILL CONTINUE MOVING SE. AN UPPER LEVEL SHORTWAVE TROUGH OVER THE
CENTRAL B.C. COAST AT 18Z WILL PASS JUST TO THE N OF WA AS IT MOVES
OVER SE B.C. BY 06Z A WEAK WARM FRONT MOVING TOWARD VANCOUVER ISLAND
WILL BRUSH THE FAR NW PART OF W WA 06Z THU THROUGH 00Z FRI.

THE AIR MASS OVER W WA IS STABLE AND MAINLY DRY WEST OF PUGET SOUND.
A MIX OF IFR FOG AND MVFR STRATUS IS PRESENT OVER MOST OF PUGET
SOUND AND THE SW INTERIOR. HIGHER VFR LAYERS FROM BKN030 TO
BKN-OVC070 ARE PRESENT FROM N PUGET SOUND UP ACROSS THE N INTERIOR.
THE CLOUD COVER OVER THE INTERIOR IS EXPECTED TO EVENTUALLY LIFT AND
BREAK UP...WITH BETTER VFR CONDITIONS THIS AFTERNOON...BUT COULD
LAST IN SOME AREAS UNTIL 21Z.

KSEA...AREAS OF LOW STRATUS SCT-BKN008-012 WILL HANG AROUND UNTIL
18Z-19Z THIS MORNING BEFORE DISSIPATING. GOOD VFR CONDITIONS ARE
EXPECTED THIS AFTERNOON. SURFACE WINDS WILL BE LIGHT W-SW THROUGH
00Z THEN SHIFT TO NW-N AROUND 03Z. KAM

&&

.MARINE...A 1025 MB SURFACE RIDGE WILL REMAIN OVER THE COASTAL AND
OFFSHORE WATERS TODAY. THIS WILL ALLOW WEAK ONSHORE FLOW TO CONTINUE
THROUGH THIS EVENING. A SCA IS IN EFFECT FOR THE CENTRAL AND E
STRAIT LATE THIS AFTERNOON AND EVENING BUT IT LOOKS MARGINAL. THE
00Z ARW-WEST MODEL HAS W WINDS PEAKING ABOUT 18 KT THIS EVENING AND
THE 06Z CANADIAN 2.5KM MODEL SHOWS LOW END SCA WINDS. I WILL HANG ON
TO THE SCA FOR NOW.

THE SURFACE RIDGE WILL SHIFT INLAND TONIGHT AS AN OFFSHORE WARM
FRONT BRUSHES THE AREA ON ITS WAY TOWARD N/CENTRAL VANCOUVER ISLAND.
THE RIDGE WILL THEN SIT OVER W WA AND ACTUALLY STRENGTHEN THURSDAY
AND FRIDAY FOR A SHORT PERIOD OF WEAK OFFSHORE FLOW. DURING THIS
PERIOD A FRONTAL ZONE WILL REMAIN OVER THE CENTRAL B.C. COAST. ON
FRIDAY NIGHT THE FRONT WILL FINALLY SAG S OVER W WA. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY IN EFFECT FROM 3 PM THIS AFTERNOON TIL
     MIDNIGHT TONIGHT FOR THE CENTRAL AND EASTERN STRAIT OF JUAN
     DE FUCA.

&&

$$

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.