Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 270414
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
915 PM PDT SUN JUL 26 2015

.SYNOPSIS...SHOWERS WILL DIMINISH TONIGHT AS AN UPPER LEVEL TROUGH
MOVES EAST OF THE CASCADES. A BROAD UPPER LEVEL RIDGE WILL BUILD
OVER THE REGION TUESDAY AND KEEP CONDITIONS DRY AND WARM THROUGH THE
END OF THE WEEK.

&&

.SHORT TERM...WATER VAPOR IMAGERY SHOWS THE AXIS OF THE UPPER LEVEL
TROUGH OVER THE REGION WAS OVER THE CASCADES AT 02Z THIS EVENING.
THE TROUGH WILL CONTINUE HEADING QUICKLY E AND SHOULD BE NEAR THE ID
BORDER AROUND 12Z. RADAR IMAGERY SHOWS THE CONVECTION OVER W WA IS
DIMINISHING RAPIDLY IN COVERAGE AND IT LOOKS LIKE THE THREAT OF
THUNDERSTORMS HAS ENDED. ISOLATED CELLS FORMED OVER MUCH W WA THIS
AFTERNOON AND LIGHTNING ACTIVITY WAS FAIRLY ACTIVE...ALTHOUGH
LIGHTNING DETECTION SYSTEMS INDICATED MOST OF THIS WAS LIGHTNING
WITHIN THE CLOUD RATHER THAN CLOUD-TO-GROUND.

MODELS REMAIN FAIRLY CONSISTENT WITH THE DEVELOPING UPPER LEVEL
RIDGING PATTERN THIS WEEK. MONDAY SHOULD BE A TRANSITION DAY WITH W
WA IN-BETWEEN THE DEPARTING UPPER LEVEL TROUGH...AND THE OFFSHORE
UPPER LEVEL RIDGE APPROACHING THE COAST. SKIES HAVE CLEARED OUT OVER
MAINLY THE N PART OF W WA THIS EVENING...BUT THE LOWER AIR MASS IS
STILL MOIST ENOUGH FOR AREAS OF LOW CLOUDS TO FORM OVERNIGHT. WITH
DRIER N-NW FLOW ALOFT OVER THE AREA THE MORNING CLOUDS SHOULD CLEAR
TO PARTLY TO MOSTLY SUNNY CONDITIONS IN THE AFTERNOON.

THE AXIS OF THE BROAD UPPER LEVEL RIDGE WILL MOVE OVER W WA ON
TUESDAY THEN REMAIN OVER THE AREA THE REST OF THE WEEK FOR SUNNY AND
WARM WEATHER. 500 MB HEIGHTS WILL GRADUALLY RISE FROM 5760 METERS ON
MONDAY...PEAKING AT AROUND 5870 METERS ON THURSDAY. WEAK W-NW LOW
LEVEL ONSHORE FLOW WILL CONTINUE IN THE AFTERNOON AND EVENINGS...BUT
IT LOOKS LIKE THERE COULD BE A WEAK NE OFFSHORE COMPONENT TO THE
FLOW DURING THE LATE NIGHT AND MORNING HOURS. THIS SHOULD HELP THE
OVERALL WARM UP THIS WEEK WITH HIGHS EXPECTED TO BE IN THE 80S OVER
MUCH OF THE INTERIOR TUESDAY AND WEDNESDAY. KAM

.LONG TERM...PREVIOUS DISCUSSION FROM THE 245 PM AFD...NO CHANGE IN
THE PATTERN THROUGH NEXT WEEKEND. DAYS WILL BE SUNNY AND NIGHTS WILL
BE CLEAR. THE HIGHEST HEIGHTS ARE ON THURSDAY WITH HIGH TEMPERATURES
IN THE 80S TO LOW 90S EXCEPT FOR 70S ON THE COAST. THERE IS SLIGHT
COOLING AFTER THAT BUT HIGHS EACH DAY FROM SEATTLE SOUTH WILL REMAIN
IN THE 85-90 RANGE. BURKE.

&&

.AVIATION...AN UPPER LEVEL TROUGH WILL MOVE EAST OF THE REGION
TONIGHT. LIGHT TO MODERATE NW FLOW ALOFT...BECOMING LIGHT NLY ON
MONDAY. AT THE SURFACE...ONSHORE FLOW WILL CONTINUE WITH HIGH
PRESSURE OFFSHORE AND LOWER PRESSURE INLAND. AIR MASS MOIST AND
BECOMING STABLE THIS EVENING. THE THREAT OF TSTMS AT THE TERMINALS
HAS PASSED WITH JUST A FEW SHOWERS OVERNIGHT. AREAS OF MVFR STRATUS
FILLING IN TONIGHT...WITH CLOUDS LIFTING TO VFR 5-6K FT BY
MIDDAY...BECOMING SCT-BKN BY LATE AFTERNOON.

KSEA...MVFR STRATUS IS EXPECTED TO DEVELOP LATE TONIGHT AND MONDAY
MORNING. N-NW WIND 4 TO 8 KT...BECOMING LIGHT VARIABLE AFTER
MIDNIGHT...THEN SWLY AFTER 18Z MONDAY.

&&

.MARINE...ONSHORE FLOW WILL PREVAIL THIS WEEK...POSSIBLY EASING A
BIT WEDNESDAY AND THURSDAY...WITH HIGH PRESSURE OFFSHORE AND LOWER
PRESSURE INLAND. SMALL CRAFT ADVISORY WEST WINDS ARE LIKELY EACH
EVENING IN THE CENTRAL AND EAST STRAIT. SCHNEIDER/DTM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA.

&&

$$

WWW.WEATHER.GOV/SEATTLE

AN ILLUSTRATED VERSION OF THIS FORECAST DISCUSSION CAN BE SEEN AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML



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