Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 260325
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
830 PM PDT SAT APR 25 2015

.SYNOPSIS...HIGH PRESSURE ALOFT WILL BUILD OVER WESTERN WASHINGTON
INTO EARLY SUNDAY. AN APPROACHING BUT WEAKENING WARM FRONT IS
EXPECTED TO INCREASE CLOUD COVER SUNDAY WITH A THREAT OF RAIN MAINLY
NEAR THE COAST. HIGH PRESSURE WILL PREVAIL AGAIN MONDAY FOR A WARMER
DAY BEFORE ANOTHER PACIFIC FRONTAL SYSTEM SWINGS ONSHORE TUESDAY FOR
ANOTHER THREAT OF RAIN AND COOLER CONDITIONS.

&&

.SHORT TERM...WITH THE SUN SETTING...THE LINGERING SHOWERS MAINLY IN
SW WASHINGTON HAVE BEEN TAPERING OFF ALONG WITH DISSIPATING CLOUDS.
WILL UPDATE THE FORECASTS TO REFLECT THE CLEARING YET COOL NIGHT
AHEAD.

LOOKING UPSTREAM...THE APPROACHING UPPER RIDGE HAD MOVED INSIDE 135W
AND THE SHORT TERM PROGS BRING THE AXIS INTO WESTERN WASHINGTON
SUNDAY. A WARM FRONT HAS CLOUD COVER MOVING ACROSS THE RIDGE AXIS.
YET WITH RISING HEIGHTS THROUGH MONDAY...EXPECT THE FRONT TO WEAKEN
AND DISSIPATE. SO THE FORECAST OF INCREASING CLOUDS SUNDAY WITH A
THREAT OF LIGHT RAIN MAINLY FROM THE OLYMPIC PENINSULA WESTWARD
LOOKS ON TRACK. THE 00Z NAM CONCURS.

THE BUILDING UPPER RIDGE PROMISES MORE CLEARING AND SUNSHINE WITH
WARMER TEMPS MONDAY...THOUGH SHORT-LIVED. THE NEXT FRONTAL SYSTEM
SPINNING OUT OF THE LONG-WAVE TROUGH POSITION NEAR 155W IS EXPECTED
TO SWING ONSHORE LATE MONDAY NIGHT INTO TUESDAY FOR ANOTHER ROUND OF
PRECIP AND COOLER TEMPS WITH A HEALTHY ONSHORE PUSH. BUEHNER

.LONG TERM...FROM THE PREVIOUS DISCUSSION...
CONFIDENCE IN THIS PERIOD REMAINED LOW. THE MODELS WERE IN
BETTER AGREEMENT AS FAR AS WED AND THU WERE CONCERNED...AND
INDICATED AN UPPER TROF WILL MOVE ACROSS THE REGION. THE PRIMARY
DIFFERENCES WERE IN THE DETAILS. BEYOND THU...THE MEDIUM RANGE
SOLUTIONS DIVERGED IN THE TIMING AND STRENGTH OF AN UPPER TROF
DEVELOPING OVER THE PACIFIC NORTHWEST LATE IN THE PERIOD. THE
FORECAST WAS...MORE OR LESS...BROADBRUSHED.

&&

.AVIATION...UPPER LEVEL LOW OVER EASTERN WASHINGTON WILL DISSIPATE
SUNDAY MORNING. TEMPORARY UPPER LEVEL RIDGE MOVING THROUGH WESTERN
WASHINGTON SUNDAY MORNING. WEAKENING FRONT REACHING THE COAST LATE
IN THE DAY. NORTHWESTERLY FLOW ALOFT BECOMING WESTERLY SUNDAY
AFTERNOON. AIR MASS STABLE.

SATELLITE AND RADAR IMAGERY SHOW SHOWERS HAVE DISSIPATED QUICKLY
THIS EVENING LEAVING MOSTLY CLEAR SKIES OVER THE AREA. WITH THE
CLEAR SKIES THERE IS THE POSSIBILITY OF FOG EARLY SUNDAY MORNING IN
THE FOG PRONE AREAS LIKE OLYMPIA. INCREASING MID LEVEL CLOUDS LATER
SUNDAY MORNING WITH THE CEILINGS LOWERING DOWN TO BETWEEN 5000-8000
FEET SUNDAY AFTERNOON. RAIN BEGINNING ALONG THE COAST IN THE MID TO
LATE AFTERNOON HOURS WITH THE RAIN HOLDING OFF OVER THE INTERIOR
UNTIL THE EVENING HOURS. CEILINGS LOWERING DOWN TO NEAR 4000 FEET
WITH THE ONSET OF THE PRECIPITATION. SOME MVFR CIGS ARE POSSIBLE
ALONG THE COAST SUNDAY EVENING.

KSEA...MOSTLY CLEAR SKIES AND LIGHT WINDS OVERNIGHT INTO EARLY
SUNDAY MORNING. INCREASING MID LEVEL CLOUDS MID MORNING WITH
CEILINGS SLOWLY LOWERING DOWN TO NEAR 7000 FEET BY 00Z MONDAY.
SOUTHERLY WINDS 4 TO 8 KNOTS LATER SUNDAY MORNING INTO THE AFTERNOON
HOURS. FELTON

&&

.MARINE...FLAT SURFACE GRADIENTS TONIGHT INTO SUNDAY MORNING WITH
WEAK HIGH PRESSURE ACROSS THE AREA. A WEAK FRONT WILL MOVE THROUGH
THE AREA LATE SUNDAY...AND SOUTHERLIES WILL PICK UP OVER THE WATERS
SUNDAY IN ADVANCE OF THE FRONT. MID TO HIGH END SMALL CRAFT ADVISORY
LEVEL WINDS ARE EXPECTED OVER THE COAST AND MARGINAL SMALL CRAFT
ADVISORY LEVEL WINDS ARE POSSIBLE OVER INLAND WATERS.

ANOTHER FRONT WILL MOVE THROUGH THE AREA TUESDAY WITH WINDS OVER THE
COASTAL WATERS SHARPLY SWITCHING FROM SOUTHERLY TO NWLY WITH THE
PASSAGE OF THE FRONT. A STRONG WESTERLY PUSH IS LIKELY IN THE STRAIT
BEHIND THE FRONT. HIGH PRESSURE WILL BUILD IN BEHIND THE FRONT ON
WEDNESDAY. FELTON/JSMITH

&&

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

&&

$$

WWW.WEATHER.GOV/SEATTLE

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






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