Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 220412
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 PM PDT MON JUL 21 2014

.SYNOPSIS...AN UPPER LEVEL TROUGH WILL MOVE SOUTH JUST OFFSHORE
THROUGH TUESDAY. THE TROUGH WILL MOVE INLAND OVER THE PACIFIC
NORTHWEST WEDNESDAY AND WEDNESDAY NIGHT. HIGH PRESSURE WILL BUILD
INTO THE AREA LATE IN THE WEEK AND STRENGTHEN OVER THE WEEKEND.

&&

.SHORT TERM...AN UPPER TROUGH WILL SAG SOUTH JUST OFF THE COAST
THROUGH TUESDAY. THE NAM SHOWS PRECIP DEVELOPING OVER THE NRN OREGON
CASCADES TUE AFTERNOON...SPREADING NORTH OVER THE WA CASCADES
THROUGH EVENING. A BAND OF RAIN DEVELOPS OVERNIGHT TUE NITE OVER WRN
WA AND PRECIP BECOMES WIDESPREAD OVER ALL OF WA ON WED AS THE UPPER
TROUGH MOVES ASHORE AND A 562DAM LOW CENTER MOVES NE THROUGH WA. THE
LOW CENTER WILL MOVE TO SE B.C. BY DAYBREAK THU AND THEN NW FLOW
ALOFT AND RISING HEIGHTS WILL CONFINE THE SHOWERS TO THE CASCADES.
PRECIP ENDS BY THU AFTERNOON WITH CLEARING.

.LONG TERM...A WARMING TREND IS ON TAP INTO THE WEEKEND AS 500MB
HEIGHTS RISE THROUGH THE 580S SAT AND SUN. HIGH TEMPS SHOULD REACH
THE 80S IN MANY PLACES OVER WRN WA THIS WEEKEND WITH CLEAR SKIES.

&&

.AVIATION...UPPER LEVEL TROUGH WELL OFFSHORE CONTINUES TO MOVE SOUTH
TODAY WITH THE SOUTHWESTERLY FLOW ALOFT. AT THE SURFACE...HIGH
PRESSURE OFFSHORE WITH LOWER PRESSURE INLAND THROUGH TUESDAY. AIR
MASS STABLE AND DRY WITH INCREASING HIGH LEVEL MOISTURE TUESDAY.

JUST A FEW CLOUDS ALONG THE EAST SLOPES OF THE OLYMPICS OTHERWISE
CLEAR SKIES ACROSS WESTERN WASHINGTON TONIGHT. SURFACE GRADIENTS
ONSHORE BUT VERY WEAK WITH KUIL-KBLI AND KHQM-KSEA UNDER A MILLIBAR
AND KOTH-KSEA UNDER 2 MILLIBARS. NO REAL INCREASE IN THE ONSHORE
FLOW EXPECTED OVERNIGHT SO WILL STAY WITH THE CLEAR SKIES WITH THE
EXCEPTION OF SOME LOW CLOUDS FORMING ALONG THE COAST TUESDAY
MORNING. AS THE UPPER LEVEL TROUGH OFFSHORE CONTINUES TO DIG ON
TUESDAY HIGH LEVEL CLOUDS EMBEDDED IN THE SOUTHWESTERLY FLOW ALOFT
WILL MOVE OVER THE AREA.

KSEA...MOSTLY CLEAR SKIES AND LIGHT WINDS THROUGH TUESDAY MORNING.
INCREASING HIGH CLOUDS TUESDAY AFTERNOON. FELTON

&&

.MARINE...HIGH PRESSURE OFFSHORE WITH LOWER PRESSURE INLAND FOR THE
NEXT SEVERAL DAYS...RESULTING IN VARYING DEGREES OF ONSHORE FLOW.
THE ONSHORE FLOW WILL WEAKEN LATER TUESDAY INTO WEDNESDAY MORNING
WHEN A WEAK SURFACE LOW MOVES INTO THE COASTAL WATERS AND DISSIPATES
THEN STRENGTHEN AGAIN LATER WEDNESDAY INTO THE REMAINDER OF THE WEEK
WITH HIGH PRESSURE REBUILDING OVER THE COASTAL WATERS. EXPECT SMALL
CRAFT ADVISORY WEST WINDS FOR THE CENTRAL AND EASTERN STRAIT OF JUAN
DE FUCA EACH EVENING INTO THE EARLY MORNING HOURS BEGINNING
WEDNESDAY EVENING. FELTON

&&

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

&&

$$

YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML






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