Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 201048
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
330 AM PDT SUN JUL 20 2014

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

&&

.SHORT TERM...A PUGET SOUND CONVERGENCE ZONE HAS DEVELOPED AND IS
BRINGING LIGHT RAIN TO THE NORTH PUGET SOUND LOWLANDS. EXPECT THIS
CONVERGENCE ZONE TO FIZZLE THROUGH THE DAY WITH SPOTTY SHOWERS
ELSEWHERE. WE MAY SEE SOME SUNBREAKS THIS 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
INTO THE AREA LATE TUESDAY AND SOUTHERLY FLOW ALOFT SHOULD RESULT IN
INSTABILITY AND SHOWERS DEVELOPING TUESDAY AFTERNOON OR EVENING.
JSMITH

.LONG TERM...RECENT GFS RUNS HAVE SLIGHTLY DELAYED THE ARRIVAL OF
THE UPPER LEVEL LOW...PROJECTING IT TO MOVE OVER WESTERN WASHINGTON
LATE WEDNESDAY EVENING INSTEAD OF WEDNESDAY AFTERNOON. HOWEVER...THE
FORECAST REMAINS THE SAME...HEAVIER AND MORE WIDESPREAD SHOWERS AND
PERHAPS A PERIOD OF CONTINUOUS SOAKING RAIN IN THE LOWLANDS ON
WEDNESDAY. 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. JSMITH

&&

.AVIATION...UPPER TROUGH SETTLING OVER THE AREA LATER TODAY.
WESTERLY FLOW ALOFT BECOMING NORTHWESTERLY. AT THE SURFACE...HIGH
PRESSURE WILL BE OFFSHORE WITH LOWER PRESSURE INLAND. AIR MASS MOIST
AND SLIGHTLY UNSTABLE.

MULTIPLE CLOUD LAYERS OVER WESTERN WASHINGTON EARLY THIS MORNING. IN
GENERAL A SCATTERED TO BROKEN LAYER AROUND 2000 FEET WITH A BROKEN
TO OVERCAST LAYER AT 3000-4000 FEET. CONVERGENCE ZONE OVER SNOHOMISH
AND NORTHERN KING COUNTY WITH AREAS OF CEILINGS BELOW 1000 FEET AND
VISIBILITIES 3-5SM WITH LIGHT RAIN.

ONSHORE FLOW CONTINUING TODAY INTO TONIGHT WITH THE CONVERGENCE ZONE
WEAKENING LATER THIS MORNING INTO THE AFTERNOON HOURS. WITH THE
ONSHORE FLOW CONTINUING EXPECT LITTLE CHANGE IN THE CONDITIONS
THROUGH THE AFTERNOON HOURS WITH THE EXCEPT OF THE LOWER LAYER
BECOMING MORE SCATTERED THIS AFTERNOON. WITH THE ONSHORE FLOW
CONTINUING TONIGHT CEILINGS WILL LOWER ONCE AGAIN OVERNIGHT INTO THE
1500-2500 FOOT RANGE WITH CEILINGS NEAR 1000 FEET ALONG THE COAST. .

KSEA...WITH THE CONVERGENCE ZONE SO CLOSE THIS MORNING WILL HAVE TO
KEEP AT LEAST A TEMPO GROUP WITH CEILINGS NEAR 2000 FEET IN THE TAF
OTHERWISE CEILINGS 3500-5000 FEET THROUGH THE AFTERNOON HOURS.
SOUTHERLY WIND 4 TO 8 KNOTS. 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 INTO
THE EARLY MORNING HOURS. FELTON

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY 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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