Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 220501
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 PM PST FRI NOV 21 2014

.SYNOPSIS...A FRONT PUSHING INTO THE CASCADES THIS EVENING WILL MOVE
EAST OF THE AREA ON SATURDAY. ANOTHER FRONT WILL MOVE THROUGH THE
AREA ON SUNDAY WITH BREEZY WINDS AND MORE MOUNTAIN SNOW. A WARM
FRONT WILL BE OVER THE AREA MONDAY....THEN AN UPPER RIDGE WILL BUILD
INTO THE AREA TUESDAY. THE RIDGE WILL MOVE INLAND WEDNESDAY AND A
FRONT MAY REACH THE AREA WEDNESDAY NIGHT OR THURSDAY.

&&

.SHORT TERM...MSAS PRESSURE ANALYSIS AN OBS INDICATE THE SURFACE
FRONT HAS PUSHED E OF PUGET SOUND AND ABOUT TO PUSH INTO THE
CASCADES AT 8 PM. STEADY PRECIPITATION ON RADAR IS NOW MOSTLY
CONFINED TO AREAS E OF PUGET SOUND ALONG THE FOOTHILLS AND
CASCADES...EXCEPT FOR SOME SHOWS MOVING DOWN THE STRAIT ASSOCIATED
WITH CONVERGENCE ALONG A WESTERLY WIND SURGE. THE WEAK SURFACE
PATTERN W OF PUGET SOUND AND 925/850MB WLY FLOW DOWN THE STRAIT WILL
BE SOMEWHAT CONDUCIVE FOR A POSSIBLE CONVERGENCE ZONE AT TIMES
TONIGHT MAINLY N OF SEATTLE. THE FRONT NOW E OF PUGET SOUND BROUGHT
LOCALLY WINDY CONDITIONS TO THE COAST AND PARTS OF THE N INTERIOR
EARLIER. WINDS ARE EASING NOW THAT THE FRONT HAS PASSED AND THE WIND
ADVISORY DROPPED EARLIER FOR THE COAST WILL ALSO BE ALLOWED TO
EXPIRE FOR THE N INTERIOR.

THE LOWER SNOW LEVELS DOWN BELOW 3000 FEET IS THE BIGGER STORY THIS
EVENING WITH UP TO 6 INCHES ALREADY REPORTED AT SNOQUALMIE PASS AND
STEVENS PASSES. THERE IS CURRENTLY A BURST OF HEAVIER SNOW OVER THE
C/CENTRAL CASCADES AFFECTING THESE PASSES SO A FEW MORE INCHES COULD
FALL BEFORE SNOW TAPERS TO SHOWERS AFTER MIDNIGHT TONIGHT. AMOUNTS
COULD REACH 8-10 INCHES AT THE PASSES...WITH OVER A FOOT AT SOME
HIGHER SKI RESORTS. STILL LOOKS JUST BELOW WARNING CRITERIA WHICH
WOULD REQUIRE A FOOT BELOW 6K FT.

SNOW WILL TAPER TO SNOW SHOWERS LATER TONIGHT AND SATURDAY WITH
MAINLY LIGHT ACCUMULATIONS OF A FEW INCHES OR LESS. ANY CONVERGENCE
ZONE COULD PUT DOWN SOME LOCALIZED HIGHER AMOUNTS IN THE CASCADES OF
SNOHOMISH/SKAGIT COUNTIES BUT IT NOT WARRANT AN EXTENSION OF THE
ADVISORY GIVEN THE UNCERTAINTY ON WHERE ANY CONVERGENCE ZONE
ENHANCEMENT MAY OCCUR. PRECIPITATION WILL FALL AS RAIN BELOW 3K FT
BUT JUST AS HIT AND MISS RAIN SHOWERS. AREAS  DOWNWIND OF THE
OLYMPICS COULD IN FACT SHADOW PART OF THE DAY SATURDAY WITH SOME
PEAKS OF SUNSHINE AT TIMES. IT WILL REMAIN COOL WITH HIGHS ONLY IN
THE UPPER 40S ACROSS THE LOWLANDS.

THE NEXT SIGNIFICANT SYSTEM TO AFFECT WRN WA WILL ARRIVE ON SUNDAY.
THIS SYSTEM WILL BE EMBEDDED IN FAST MOVING WLY FLOW WHICH WILL HELP
LIMIT OVERALL PRECIPITATION AMOUNTS. WARM ADVECTION RAIN WILL FILL
IN ACROSS WRN WA SUNDAY MORNING...THEN THE COLD FRONT WILL SPREAD
HEAVIER RAIN INTO THE AREA DURING THE AFTERNOON. GIVEN THE
PROGRESSIVE NATURE OF THE FRONT...RAIN SHOULD TAPER TO SHOWERS BY
SUNDAY EVENING. 850 MB TEMPS MAY STAY DOWN NEAR -2C WHICH SHOULD
SUPPORT SNOW DOWN TO SOME LOWER PASSES SUCH AS SNOQUALMIE BUT
HEAVIER SNOW AMOUNTS WILL PROBABLY BE FROM STEVENS PASS N TO MT.
BAKER. MODEL QPF AMOUNTS SUGGEST NEAR 1 INCH LIQUID OVER THE
CASCADES WHICH WOULD BE ENOUGH FOR WARNING AMOUNTS OF
SNOW...ESPECIALLY FOR PLACES LIKE PARADISE...AND MOUNT BAKER FAVORED
BY BOTH S AND W FLOW. THIS CAN BE RE-EVALUATED BY THE NEXT SHIFT.

.LONG TERM...NO UPDATE FROM PREVIOUS DISCUSSION...A WARM FRONT WILL
MOVE THROUGH THE REGION ON MONDAY AND HEIGHTS RISE THROUGH TUE AND
TUE NITE AS THE PRECIP ENDS. A RIDGE AXIS ALONG THE WEST COAST
TUESDAY NIGHT PROGRESSES INLAND TO ABOUT IDAHO BY LATE WED AS A
FRONT REACHES THE PACNW WED NITE AND THU MORNING...WITH THE MAIN
PUNCH OF THE FRONT STAYING NORTH OF WRN WA. A SPLITTY SYSTEM MOVES
IN OVER THE WEST COAST LATER THU AND FRI.

&&

.HYDROLOGY...RIVER FLOODING IS NOT EXPECTED THE NEXT 7 DAYS.

&&

.AVIATION...THE COLD FRONT THAT MOVED ACROSS THE AREA EARLY THIS
EVENING IS NOW WELL EAST OF THE CASCADES. MODERATELY STRONG LOW
LEVEL ONSHORE FLOW IS FOLLOWING THE FRONT AT THE SURFACE WHILE FLOW
ALOFT IS WESTERLY. THE AIR MASS IS SOMEWHAT MOIST AND UNSTABLE.

EXPECT SHOWERS THROUGH SATURDAY EVENING...ESPECIALLY AROUND A PUGET
SOUND CONVERGENCE ZONE AND ALONG THE WEST SLOPES OF THE OLYMPICS AND
CASCADES. SHOWERS WILL BRIEFLY INCREASE FOR A FEW HOURS
SATURDAY MORNING AS A WEAK UPPER LEVEL SHORTWAVE TROUGH ALOFT MOVES
ACROSS THE AREA. THE MOST UNSTABLE AIR WILL REMAIN OFFSHORE WITH A
CHANCE OF TSTMS SATURDAY OVER THE WASHINGTON COASTAL WATERS. EXPECT
MAINLY MVFR CEILINGS WITH LOCAL IFR CONDITIONS AROUND KPAE TONIGHT
WITH A CONVERGENCE ZONE. VIS WILL GENERALLY REMAIN P6SM IN LIGHT
SHOWERS...LOCALLY FALLING TO 3-5SM -SHRA IN HEAVIER SHOWER ACTIVITY.

KSEA...P6SM -SHRA BKN-OVC010-015 WITH LAYERS ABOVE. WIND SWLY
10-14KT G25 KT EASING TO 9-12 KT SATURDAY. CONVERGENCE ZONE ACTIVITY
IS EXPECTED TO REMAIN 10 NM OR MORE N OF THE TERMINAL THROUGH
SATURDAY. ALBRECHT

&&

.MARINE...A RATHER ACTIVE PERIOD IS EXPECTED OVER THE WATERS THROUGH
THE MIDDLE OF THE UPCOMING WEEK AS A SERIES OF SYSTEMS MOVE THROUGH
THE WATERS.

MODERATELY STRONG POST FRONTAL ONSHORE FLOW IS GIVING SMALL CRAFT
ADVISORY CONDITIONS TO ALL OF THE WATERS...EXCEPT TO THE CENTRAL AND
EAST STRAIT OF JUAN DE FUCA WHERE GALES ARE OCCURRING. WINDS WILL
SLOWLY RELAX DURING THE DAY ON SATURDAY.

ANOTHER FRONTAL SYSTEM WILL SWEEP ACROSS THE WATERS LATE SATURDAY
NIGHT AND SUNDAY MORNING. THIS FRONT WILL BRING SMALL CRAFT ADVISORY
CONDITIONS TO ALL OF THE WATERS. GALE FORCE WINDS ARE POSSIBLE OVER
PORTIONS OF THE COASTAL WATERS AND THE ENTRANCES TO THE STRAIT AS
THE FRONT MOVES THROUGH. WILL LOOK AT ALL OF THE INCOMING 00Z
GUIDANCE BEFORE ISSUING A GALE WATCH FOR PORTIONS OF THE WATERS FOR
THIS SYSTEM.

ONSHORE FLOW MAY INCREASE AGAIN TUE NIGHT OR WED AS A LOW MOVES BY
TO THE NORTH OF THE AREA. ALBRECHT

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...SNOW ADVISORY FOR THE NORTH AND CENTRAL CASCADES THROUGH
     MIDNIGHT TONIGHT.
PZ...GALE WARNING CENTRAL STRAIT OF JUAN DE FUCA AND EAST ENTRANCE
     SMALL CRAFT ADVISORY REMAINING WATERS.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.

&&

$$

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