Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 152209
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PDT MON SEP 15 2014

.SYNOPSIS...AN APPROACHING WEAK UPPER LEVEL TROUGH WILL BRING COOLER
MARINE AIR AND MORE CLOUD COVER TUESDAY. AN UPPER LEVEL TROUGH WILL
BRING AT LEAST A CHANCE OF SHOWERS WEDNESDAY AFTERNOON THROUGH
FRIDAY...WITH SHOWERS MOST LIKELY ON THURSDAY. SUNNY AND DRY WEATHER
UNDER A STRONG UPPER RIDGE IS LIKELY OVER THE WEEKEND.

&&

.SHORT TERM...SKIES ARE CLEAR THIS AFTERNOON OVER WESTERN WASHINGTON
THOUGH STRATUS IS CREEPING NORTH ALONG THE SOUTH COAST. HIGHS TODAY
WILL BE WELL INTO THE 80S EVERYWHERE WITH A FEW PLACES TOUCHING 90.

THE STRATUS ON THE SOUTH COAST IS A HARBINGER OF MORE WIDESPREAD
CLOUDINESS TUESDAY. SURFACE GRADIENTS WILL TURN WEAKLY ONSHORE
TONIGHT WHILE AN UPPER LEVEL DISTURBANCE MOVES SOUTH TO NORTH OVER
THE AREA. THIS WILL ALLOW STRATUS TO SPREAD INLAND SOMEWHAT
OVERNIGHT. MOST LIKELY THE STRATUS WILL COVER LOWLAND AREAS MAINLY
WEST OF PUGET SOUND...WITH SOME CLEARING IN THE AFTERNOON. THE
MARINE INFLUENCE WILL LOWER TEMPERATURES INTO THE 70S ON TUESDAY.

A DEEPER LOW OFF THE CALIFORNIA COAST WILL SEND SOME IMPULSES
NORTHEAST INTO WASHINGTON BEGINNING WEDNESDAY. THERE WILL BE ABOUT A
THREE DAY PERIOD WITH PLENTY OF CLOUDS AND AT LEAST A CHANCE OF
SHOWERS LASTING THROUGH ABOUT FRIDAY EVENING. THE HIGHEST POPS ARE
ON THURSDAY...IN THE LIKELY RANGE...AND IF MODEL TRENDS CONTINUE THE
POPS MAY EVENTUALLY GO HIGHER AND THE WEATHER MIGHT SIMPLY BE RAIN
RATHER THAN SHOWERS. HIGHS WILL BE MAINLY IN THE 70S WEDNESDAY AND
MAINLY IN THE 60S THURSDAY. BURKE

.LONG TERM...ON FRIDAY THERE WILL BE SOME RESIDUAL SHOWERS...MOSTLY
IN THE MOUNTAINS. AN UPPER RIDGE BUILDS OVER THE WEEKEND WITH THE
GFS SHOWING HEIGHTS IN THE MID 580S BUT THE EURO PUSHING NEARLY TO
590DM. SKIES WILL BE SUNNY AND TEMPERATURES SHOULD REACH AT LEAST
THE LOW 80S IN MANY PLACES BY SUNDAY. THE GFS HAS A WEAK SYSTEM
APPROACHING BY MONDAY SO LOWER TEMPERATURES ARE LIKELY AND THERE
WILL BE A CHANCE OF SHOWERS. BURKE

&&

.AVIATION...HIGH PRESSURE ALOFT WILL SHIFT E INTO THE INTERIOR PAC
NW AND GREAT BASIN TONIGHT AND TUESDAY. A WEAK UPPER TROUGH OFF THE
CA/OREGON COAST WILL DISSIPATE AS IT LIFTS NE INTO THE AREA TONIGHT.
LIGHT SW FLOW ALOFT BECOMING MODERATELY STRONG. STABLE ATMOSPHERE
AND DRY ALOFT. BECOMING MOIST IN THE LOW LEVELS AS MARINE STRATUS
DEVELOPS ALONG THE COAST TONIGHT...THEN SPREADS THROUGH THE STRAIT
AND CHEHALIS GAP INTO SRN PUGET SOUND BY EARLY MORNING. IFR CIGS ARE
LIKELY ALONG THE COAST AND ALSO AT KOLM. THE KSEA/KBFI TERMINALS
WILL BE ON THE EDGE OF MARINE STRATUS...BUT ANY STRATUS OVER PUGET
SOUND SHOULD BE BRIEF AND CLEAR BY 18Z.

KSEA...NLY WIND 4 TO 8 KT...BECOMING LIGHT LATE THIS EVENING...THEN
SWITCHING TO SWLY AFTER 12Z TUESDAY MORNING. A SHORT 2-4 HOUR PERIOD
OF IFR STRATUS IS STILL POSSIBLE AT THE TERMINAL AFTER 12Z. ANY
STRATUS WILL LIKELY BE SHALLOW BELOW 500 FEET AND BURN OFF BY
17-18Z.

&&

.MARINE...THE THERMALLY INDUCED TROUGH OVER THE INTERIOR WATERS THIS
EVENING WILL SHIFT E OF THE CASCADES LATER TONIGHT. THE FLOW WILL
BECOME ONSHORE ALONG THE COAST THIS EVENING...AND SWITCHING TO
ONSHORE FLOW OVER THE INTERIOR WATERS BY EARLY TUESDAY MORNING.
GRADIENTS WILL INCREASE THROUGH THE STRAIGHT OF JUAN DE FUCA THROUGH
THE DAY WITH SMALL CRAFT WESTERLIES LIKELY DEVELOPING DURING THE
AFTERNOON AND EVENING HOURS.

LIGHT ONSHORE FLOW WILL LIKELY DOMINATE THE PATTERN THROUGH THE REST
OF THE WEEK.

&&

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

&&

$$

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