Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 261621
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
921 AM PDT WED AUG 26 2015


.SYNOPSIS...A BROAD UPPER LEVEL RIDGE OVER THE WESTERN US WILL
KEEP HIGH PRESSURE ALOFT OVER WESTERN WASHINGTON THROUGH THURSDAY.
AN APPROACHING UPPER LEVEL LOW WILL USHER IN A MORE ACTIVE
WEATHER PATTERN BEGINNING THURSDAY NIGHT AND EXTENDING THROUGH
EARLY NEXT WEEK. THIS PATTERN WILL LIKELY BRING THE MOST
SIGNIFICANT RAINFALL TO THE REGION SINCE THE START OF SUMMER. IN
ADDITION TO PRECIPITATION EXPECT NEAR NORMAL HIGH TEMPERATURES TO
FALL BELOW NORMAL FRIDAY AND STAY THERE THROUGH WEDNESDAY.

&&

.SHORT TERM...A FEW MID AND HIGH CLOUDS OVER THE REGION THIS
MORNING...OTHERWISE A FINE SUNNY DAY. HIGH TEMPERATURES TODAY
WILL REACH THE MID 70S ALONG THE COAST AND THE MID 70S TO JUST
OVER 80 THROUGH THE INTERIOR LOWLANDS.

THE VERY BROAD UPPER LEVEL RIDGE OVER THE WESTERN US WILL REMAIN
IN PLACE TODAY WITH WEAK LOW LEVEL ONSHORE FLOW INCREASING A BIT
THIS AFTERNOON AND EVENING. THURSDAY WILL SEE SIMILAR
CONDITIONS WITH INCREASING MID AND HIGH LEVEL CLOUDS. THE BIG
CHANGE TO THE PATTERN WILL BEGIN THURSDAY NIGHT AS AN UPPER LEVEL
SHORTWAVE TROUGH BEGINS TO MAKE ITS WAY INTO THE GULF OF
ALASKA FROM THE BERING SEA...THIS SYSTEM WILL MERGE WITH THE
UPPER LEVEL LOW THAT HAS BEEN LINGERING OVER THE EAST PACIFIC...
HELPING NUDGE THE DOWNSTREAM RIDGE AND WHOLE LARGE SCALE UPPER
LEVEL PATTERN EASTWARD.

AS THE EAST PACIFIC UPPER LEVEL LOW BEGINS TO APPROACH THE
AREA...A SERIES OF EMBEDDED UPPER LEVEL WAVES WILL BRING SHOWERS
TO WESTERN WASHINGTON. MODELS IN DECENT AGREEMENT ON THE FIRST
REACHING THE WASHINGTON COAST EARLY FRIDAY MORNING...SPREADING
INLAND AND NORTH THROUGH THE DAY. THERE WILL LIKELY BE A SLIGHT
BREAK FRIDAY NIGHT FOLLOWED BY ANOTHER ROUND EARLY SATURDAY
MORNING. HEAVIEST PRECIPITATION GENERALLY LOOKS TO BE FOCUSED ON
THE COAST...OLYMPICS...AND NORTH CASCADES FOR BOTH OF THESE
EMBEDDED FEATURES. IN ANY CASE THIS WILL...IN EFFECT BE A FAIRLY
DRAMATIC SHIFT IN WEATHER FOR THE REGION FROM DRY AND WARM TO MUCH
WETTER AND COOL.

.LONG TERM...FROM PREVIOUS DISCUSSION...THE MEDIUM RANGE
SOLUTIONS WERE IN FAIRLY GOOD AGREEMENT THAT THE WEATHER PATTERN
OVER THE PACIFIC NORTHWEST WILL BE COOL...WET... AND LOCALLY WINDY
DURING THIS PERIOD...ESPECIALLY THIS WEEKEND. SOME PLACES /LIKE IN
THE MOUNTAINS/ COULD RECEIVE OVER 2 INCHES OF RAIN THIS
WEEKEND...WHICH WOULD HELP PUT OUT OR REDUCE THE SIZE OF THE
ONGOING WILDFIRES IN WESTERN WA.

THE MAIN DIFFERENCES IN THE MEDIUM RANGE SOLUTIONS DURING THIS
PERIOD CONCERNED THE DETAILS...ESPECIALLY IN REGARDS TO THE TIMING
AND STRENGTH OF THE SYSTEMS IMPACTING THE CWA. THE INHERITED POPS
WERE RAISED AND DAYTIME TEMPS FOR THE MOUNTAINS WERE LOWERED TO
MATCH CLOSER TO THE MODELS CONSENSUS.

&&

.AVIATION...DRY AND STABLE SOUTHWEST FLOW ALOFT WILL CONTINUE OVER
W WA THROUGH THURSDAY...BETWEEN A LARGE UPPER LEVEL LOW OFFSHORE
ALONG ROUGHLY 135W AND A LARGE UPPER LEVEL RIDGE OVER THE ROCKIES.
WITH THE DRY AND STABLE AIR MASS ONLY AREAS OF HIGH CLOUDS ARE
EXPECTED TO DRIFT ACROSS THE REGION.

A WEAK SURFACE RIDGE OVER THE WA COAST WILL MAINTAIN JUST WEAK
ONSHORE FLOW TONIGHT...SO JUST PATCHY MORNING STRATUS IS POSSIBLE
ALONG THE COAST...IN THE STRAIT OF JUAN DE FUCA AND INLAND FROM
HOQUIAM.

KSEA...GOOD VFR CONDITIONS WILL CONTINUE THROUGH THURSDAY WITH JUST
HIGH CLOUDS AT TIMES. SURFACE WINDS WILL BE W TO NW 3-7 KT THROUGH
THIS AFTERNOON SHIFTING TO THE N THIS EVENING. KAM

&&

.MARINE...A WEAK SURFACE RIDGE WILL REMAIN OVER THE WA COAST WITH
LOWER PRESSURE OVER E WA THROUGH EARLY FRIDAY. ONSHORE FLOW WILL
REMAIN WEAK...BUT THERE WILL LIKELY BE A FEW HOURS OF SMALL CRAFT
ADVISORY WEST WINDS IN THE CENTRAL AND EASTERN STRAIT OF JUAN DE
FUCA THE NEXT COUPLE EVENINGS.

SOUTHERLY FLOW WILL INCREASE THIS WEEKEND AS A SERIES OF FRONTAL
SYSTEMS REACH THE REGION. SMALL CRAFT ADVISORY SOUTHERLY WINDS ARE
LIKELY FOR THE COASTAL WATERS AND POSSIBLE FOR SOME OF THE INLAND
WATERS SATURDAY AND SUNDAY. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 5 PM THIS AFTERNOON TO 3 AM PDT
     THURSDAY FOR CENTRAL U.S. WATERS STRAIT OF JUAN DE FUCA-
     EAST ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA.

&&

$$

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