Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 272123
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
230 PM PDT THU AUG 27 2015

.SYNOPSIS...A FRONT JUST OFF THE COAST WILL BRING RAIN TO THE COAST
OVERNIGHT. FRIDAY WILL BE A RAINY DAY ACROSS WESTERN WASHINGTON WITH
THE FRONT MOVING SLOWLY ACROSS THE REGION. A STRONGER FRONTAL SYSTEM
WILL ARRIVE SATURDAY WITH RATHER BLUSTERY WEATHER EXPECTED. AN UPPER
LEVEL TROUGH WILL SHIFT OVER THE REGION THROUGH THE MIDDLE OF NEXT
WEEK.

&&

.SHORT TERM...CLOUDS WILL INCREASE TONIGHT AND A FRONT JUST OFFSHORE
WILL SPREAD RAIN ON TO THE COAST. RAIN WILL REACH THE INLAND PORTION
OF WRN WA BY DAYBREAK FRIDAY AND FRIDAY SHOULD BE A RAINY DAY OVER
WRN WA. WE MAY SEE A BREAK IN THE RAIN FRIDAY NIGHT BEFORE A SECOND
FRONT ARRIVES SATURDAY...WHICH LOOKS STRONGER. TOTAL RAINFALL FROM
THE FRONT FRIDAY AND THE STRONGER FRONTAL SYSTEM ON SATURDAY SHOULD
BE IN THE 1-3 INCH RANGE FOR MUCH OF WRN WA...PERHAPS HIGHER UP
AROUND MOUNT BAKER AND OF COURSE LESS AROUND PORT ANGELES. IT WILL
BE BLUSTERY SATURDAY WITH GALES POSSIBLE FOR THE MARINE AREAS AND
WIND ADVISORIES POSSIBLE OVER LAND.

.LONG TERM...AN UPPER LEVEL TROUGH WILL SHIFT THROUGH THE PACIFIC
NORTHWEST THROUGH THE FIRST HALF OF THE WEEK. THE SNOW LEVEL IN THE
MOUNTAINS OUGHT TO BOTTOM OUT AROUND 6000 FT AND LOWLAND TEMPS WILL
BE BELOW NORMAL. THERE WILL BE SHOWERS AT TIMES...BUT ALSO SOME
PARTLY SUNNY PERIODS.

&&

.AVIATION...SW FLOW ALOFT WILL CONTINUE OVER W WA THIS EVENING.
MOISTURE WILL INCREASE IN THE SW FLOW AFTER 05Z WITH CIGS BKN-OVC060-
100 DEVELOPING. A WEAK FRONT WILL MOVE UP OVER THE AREA FROM THE SW
WHICH WILL BRING LIGHT RAIN AND MVFR CIGS TO THE COAST AFTER 08Z AND
TO THE W WA INTERIOR AFTER 12Z. THERE COULD BE SOME LOCAL IFR CIGS
ALONG THE COAST. BEHIND THE FRONT...CIGS SHOULD LIFT TO BKN030-050
FRIDAY AFTERNOON.

KSEA...GOOD VFR CONDITIONS THROUGH 05Z WITH SCT-BKN CIRRUS OVER THE
AREA. MOISTURE FROM AN APPROACHING FRONT WILL ALLOW CIGS BKN070-100
TO DEVELOP AFTER 05Z. CIGS ARE EXPECTED TO LOWER BELOW BKN050 AFTER
12Z WITH SOME LIGHT RAIN DEVELOPING. SURFACE WINDS WILL REMAIN
SOUTHERLY 4-8 KT. KAM

&&

.MARINE...A WEAK SURFACE RIDGE WILL REMAIN OVER THE WA COAST THROUGH
FRIDAY WHILE LOWER PRESSURE CONTINUES OVER E WA. THIS WILL KEEP
ONSHORE PRESSURE GRADIENTS WEAK...ALTHOUGH THERE IS STILL A FAIR
LIKELIHOOD OF BORDERLINE SMALL CRAFT ADVISORY WEST WINDS IN THE
CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA THIS EVENING.

A SERIES OF FRONTAL SYSTEMS WILL MOVE ACROSS THE REGION FRIDAY INTO
EARLY NEXT WEEK. THESE SYSTEMS WILL INCREASE THE SOUTHERLY FLOW OVER
WA WATERS WITH SCA WINDS LIKELY AT TIMES. A WEAK FRONT MOVING NE
ACROSS THE COASTAL WATERS FRIDAY COULD GENERATE BORDERLINE SCA S
WINDS OVER THE NORTHERN COASTAL WATERS.

THE 12Z MODELS ARE CONSISTENT WITH EARLIER RUNS INDICATING ANOTHER
STRONGER FRONTAL SYSTEM WILL MOVE N ACROSS W WA AND THE COASTAL
WATERS SATURDAY...FOLLOWED BY A TROUGH MOVING RAPIDLY ACROSS THE
AREA FROM THE W SATURDAY AFTERNOON. THE GFS AND UW-WRF SHOW GALE
FORCE WINDS OVER PARTS OF THE COASTAL WATERS AS WELL AS THE
CENTRAL/E STRAIT...PUGET SOUND...AND THE N INLAND WATERS. THE
AFTERNOON FORECAST IS BASED LARGELY ON THE UW-WRF. THIS LOOKS LIKE
AN UNUSUALLY STRONG SYSTEM FOR AUGUST.

AN ACTIVE PATTERN WILL CONTINUE SUNDAY AND MONDAY WITH SCA WINDS
MAINLY OVER THE COASTAL WATERS. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY TONIGHT CENTRAL AND EAST STRAIT
OF JUAN DE FUCA. GALE WATCH SATURDAY CENTRAL AND EAST STRAIT...NORTH
INLAND WATERS...PUGET SOUND AND HOOD CANAL...COASTAL ZONES 153 156
173 176.

&&

$$

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