Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 200420
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
920 PM PDT SAT JUL 19 2014

.SYNOPSIS...A WEAK UPPER TROUGH WILL MOVE THROUGH THE AREA SUNDAY.
AN UPPER LEVEL LOW WILL BRING SHOWERS TUESDAY NIGHT AND WEDNESDAY.
HIGH PRESSURE WILL REBUILD LATE IN THE WEEK.

&&

.SHORT TERM...SHOWERS OR DRIZZLE IS MAINLY CONFINED TO THE CASCADES
THIS EVENING...BUT THERE IS A HINT OF A WEAK PSCZ FORMING ON RADAR.
MOIST ONSHORE FLOW WILL PREVAIL SUNDAY AND A WEAK UPPER TROUGH WILL
REACH THE AREA. THERE WILL CONTINUE TO BE SPOTTY LIGHT SHOWERS
THROUGH SUNDAY AND PARTLY SUNNY SKIES ARE EXPECTED OVER THE LOWLANDS
SUNDAY AFTERNOON. THE UPPER FLOW WILL BACK FROM WESTERLY TO
SOUTHWEST MONDAY AS A DEEP UPPER LOW STARTS DIGGING SOUTHEAST OFF
THE COAST OF BRITISH COLUMBIA. THE AIR MASS WILL DRY SOMEWHAT AS
ONSHORE FLOW WEAKENS. WE ARE LIKELY TO START THE DAY WITH CLOUDY
SKIES...BUT THE AFTERNOON SHOULD BE PARTLY TO MOSTLY SUNNY. THE
UPPER LOW WILL TRACK SOUTHEAST TO THE AREA LATE TUESDAY AND
SOUTHERLY FLOW ALOFT SHOULD RESULT IN INSTABILITY AND SHOWERS
DEVELOPING TUESDAY AFTERNOON OR EVENING.

.LONG TERM...THE UPPER LOW WILL MOVE THROUGH WESTERN WASHINGTON ON
WEDNESDAY FOR HEAVIER AND MORE WIDESPREAD SHOWERS...AND THERE MAY BE
A PERIOD OF CONTINUOUS SOAKING RAIN. THE SHOWERS WILL DECREASE
WEDNESDAY NIGHT AND THURSDAY MORNING AS THE TROUGH MOVES EAST OF THE
CASCADES AND AN UPPER RIDGE STARTS BUILDING OFFSHORE. HIGH PRESSURE
ALOFT AND WEAK ONSHORE FLOW WILL LIKELY PREVAIL FRIDAY AND SATURDAY
FOR MOSTLY SUNNY DAYS.

&&

.AVIATION...A WEAK UPPER LEVEL DISTURBANCE WILL SWING THROUGH THE
REGION THIS EVENING WITH AN UPPER TROUGH SETTLING OVER THE AREA ON
SUNDAY. AT THE SURFACE...HIGH PRESSURE WILL BE OFFSHORE WITH LOWER
PRESSURE INLAND. AIR MASS MOIST AND SLIGHTLY UNSTABLE.

LOW CLOUDS REMAIN ALONG THE COAST...DOWN THE STRAIT AND OVER THE
LOWER CHEHALIS VALLEY THIS EVENING WITH CEILINGS AOB 1000 FEET.
MULTIPLE CLOUD LAYERS ELSEWHERE WITH GENERALLY A SCATTERED SC DECK
AROUND 2000 FEET AND A BROKEN DECK BETWEEN 4500 AND 7000 FEET. IN
ADDITION A WEAK CONVERGENCE ZONE OVER SNOHOMISH COUNTY IS CAUSING
CEILINGS BELOW 500 FEET AND VISIBILITIES AS LOW AS MILE.

ONSHORE FLOW WILL CONTINUE OVERNIGHT WITH THE LOWER STRATUS MOVING
EASTWARD OVERNIGHT REACHING THE CENTRAL PUGET SOUND IN THE EARLY
MORNING HOURS ON SUNDAY WITH WIDESPREAD CEILINGS 1000-2000 FEET WITH
LOCAL CEILINGS BELOW 1000 FEET. CONDITIONS WILL SLOWLY IMPROVE LATER
SUNDAY MORNING INTO SUNDAY AFTERNOON WITH CEILINGS UP NEAR 3000 FEET
BY LATE SUNDAY AFTERNOON OVER THE INTERIOR. WITH THE CONTINUING
ONSHORE FLOW LITTLE IMPROVEMENT EXPECTED ALONG THE COAST. THE WEAK
CONVERGENCE ZONE WILL CONTINUE OVER SNOHOMISH INTO SUNDAY MORNING.

KSEA...LOWER STRATUS ARRIVING AT THE TERMINAL 09Z-12Z WITH CEILINGS
NEAR 1000 FEET. CONDITIONS STARTING TO IMPROVE LATE SUNDAY MORNING
WITH THE IMPROVING TREND CONTINUING INTO THE AFTERNOON HOURS.
CEILINGS NEAR 3000 FEET BY LATE SUNDAY AFTERNOON. SOUTHERLY WIND
10-15 KNOTS WILL EASE TO 5-10 KNOTS SUNDAY MORNING. FELTON

&&

.MARINE...HIGH PRESSURE WILL BE OFFSHORE WITH LOWER PRESSURE INLAND
FOR THE NEXT SEVERAL DAYS...RESULTING IN VARYING DEGREES OF ONSHORE
FLOW. THIS WILL GENERALLY PRODUCE SMALL CRAFT ADVISORY WEST WINDS
FOR THE CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA EACH EVENING. FOR
THIS EVENING...THE ONSHORE FLOW IS STRONG ENOUGH FOR GALE FORCE
WINDS IN THE CENTRAL AND EAST STRAIT UNTIL EARLY SUNDAY MORNING.
FELTON

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...GALE WARNING 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




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