Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 161548
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT TUE SEP 16 2014

.SYNOPSIS...ONSHORE FLOW WILL BRING CLOUDS AND LOWER TEMPERATURES
TODAY. AN UPPER LEVEL TROUGH WILL BRING A CHANCE OF SHOWERS TO THE
AREA WEDNESDAY THROUGH FRIDAY NIGHT...WITH SHOWERS MOST LIKELY ON
THURSDAY. AN UPPER LEVEL RIDGE WILL BUILD OVER THE REGION THIS
WEEKEND FOR WARMER AND DRY WEATHER.

&&

.SHORT TERM...SATELLITE AND RADAR IMAGES SHOW A WEAK SHORT WAVE
CONSISTING MAINLY OF MID AND HIGH LEVEL CLOUDS MOVING SOUTH TO NORTH
THROUGH WESTERN WASHINGTON THIS MORNING. SO FAR THERE HAVE BEEN
SEVERAL TRACE AMOUNTS IN SPRINKLES BUT ONLY ONE INSTANCE OF
MEASURABLE PRECIPITATION...0.01 INCH AT KOLM. THIS BAND OF CLOUDS
WILL BE OUT OF THE STATE BY NOON OR SO. SOME MARINE STRATUS THAT
PENETRATED PART WAY INLAND OVER THE SOUTHWEST WILL ALSO RETREAT TO
THE COAST. SURFACE FLOW HAS BEEN SOLIDLY ONSHORE SINCE LAST NIGHT SO
HIGHS TODAY WILL BE CONSIDERABLY LOWER THAN YESTERDAY...MAINLY 70S
INLAND AND 60S COAST.

FORECAST REMAINS UNCHANGED WITH WEDNESDAY THROUGH FRIDAY HAVING AT
LEAST A CHANCE OF SHOWERS...AND SHOWERS MOST LIKELY ON THURSDAY. AN
UPPER LEVEL LOW OFF THE NORTHERN CALIFORNIA COAST WILL SPIN IMPULSES
NORTHEAST EACH DAY. BY THURSDAY AN UPPER LEVEL TROUGH IS MOVING
THROUGH WESTERN WASHINGTON. BURKE

.LONG TERM...PREVIOUS DISCUSSION...THE UPPER LEVEL TROUGH WILL MOVE
OVER E WA THURSDAY EVENING WITH DIMINISHING SHOWERS OVER W WA.
HOWEVER ANOTHER WEAKER UPPER LEVEL SHORTWAVE TROUGH MOVING ONSHORE
WILL PROLONG THE CHANCE OF SHOWERS INTO FRIDAY EVENING. GFS AND
ECMWF AGREE WELL ON BUILDING A STRONG UPPER LEVEL RIDGE JUST
OFFSHORE FRIDAY NIGHT THEN MOVING IT INLAND ON SATURDAY. THIS WILL
BRING ANOTHER PERIOD OF E-NE LOW LEVEL OFFSHORE FLOW...WHICH COULD
PUSH MAX TEMPS BACK UP INTO THE 80S THIS WEEKEND...PARTICULARLY ON
SUNDAY. BOTH MODELS HAVE THE RIDGE SHIFTING E OVER W MT SUNDAY NIGHT
ALLOWING A WEAKENING FRONT TO APPROACH THE COAST ON MONDAY. HOWEVER
THE FRONT COULD BE WEAK AND SLOW ENOUGH TO EKE OUT A MOSTLY SUNNY
DRY MONDAY AS WELL. KAM

&&

.AVIATION...A WEAK UPPER TROUGH OVER WA TODAY WILL LIFT NE OF THE
AREA TONIGHT. BROADER LOW PRESSURE ALOFT WILL REMAIN OFFSHORE
THROUGH WED. LIGHT SW FLOW ALOFT. THE AIR MASS IS MOIST AND WEAKLY
UNSTABLE THIS MORNING...JUST ENOUGH TO BREAK UP SOME OF THE LOWER
STRATUS DECK ACROSS THE LOWLANDS. MID CLOUDS AND A FEW ISOLATED
SHOWERS WILL DECREASE LATER TODAY. THE AIR MASS WILLS STABILIZE
TONIGHT WITH ANY PATCHY MVFR STRATUS SHORT LIVED WED MORNING.
ANOTHER SURGE OF MID AND UPPER LEVEL MOISTURE WILL ARRIVE LATE
TONIGHT AND WED. A FEW HIGH BASED SHOWERS WILL AGAIN BE POSSIBLE.

KSEA...MVFR STRATUS WILL BRIEFLY AFFECT THE TERMINAL THIS
MORNING...OTHERWISE MID AND HIGH CLOUDS TODAY. ANOTHER SURGE OF
MID/HIGH CLOUDS MAY ARRIVE LATE TONIGHT AND WED. PATCHY MVFR STRATUS
COULD ALSO FORM AT OR NEAR THE TERMINAL FOR A FEW HOURS WED MORNING.
ONSHORE FLOW TODAY WITH S TO SW WIND LESS THAN 10 KT. DTM

&&

.MARINE...A WLY PUSH IS UNDERWAY IN THE STRAIT OF JUAN DE FUCA THIS
MORNING. SMALL CRAFT WINDS TO 25 KT ARE LIKELY THROUGH ABOUT
MIDNIGHT BEFORE DECREASING. AFTER THE MARINE PUSH TODAY THE ONSHORE
FLOW WILL BE FAIRLY LIGHT AS WEATHER SYSTEMS MOVING THROUGH THE AREA
ARE EXPECTED TO BE RATHER WEAK. DTM

&&

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

&&

$$

WWW.WEATHER.GOV/SEATTLE

YOU CAN SEE AN ILLUSTRATED VERSION OF THIS FORECAST DISCUSSION AT
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