Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 241554
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT WED JUN 24 2015

.SYNOPSIS...WEST FLOW ALOFT AND A WEAK UPPER LEVEL TROUGH JUST
OFFSHORE WILL CONTINUE SPREADING MID AND HIGH LEVEL CLOUDS ACROSS
WESTERN WASHINGTON TODAY. A STRONG UPPER LEVEL RIDGE WILL BUILD OVER
THE REGION THURSDAY THROUGH EARLY NEXT WEEK FOR MAINLY SUNNY AND HOT
WEATHER. A WEAK UPPER LEVEL TROUGH COULD TRIGGER THUNDERSTORMS
ACROSS WESTERN WASHINGTON LATER THIS WEEKEND.

&&

.SHORT TERM...IR/VISIBLE SATELLITE IMAGERY SHOWS A MASS OF CLOUDS
JUST OFFSHORE ASSOCIATED WITH A WEAK SHORT WAVE MOVING INTO WRN WA
THIS MORNING. MODELS AGREE THAT THIS FEATURE WILL DISSIPATE RAPIDLY
AS IT MOVES INLAND WITH MAINLY MID AND HIGHER LEVEL CLOUDS OVER THE
INTERIOR THROUGH THE DAY. BOTH FORKS AND TOFINO TO THE  NORTH HAD
LIGHT RAIN THIS PAST HOUR AND THE KLGX COASTAL RADAR
.2 SLICE SHOWS SOME PRECIPITATION ECHOS MOVING ONTO THE COAST. THE
CHANCE POPS FOR THE COAST/OLYMPICS LOOK APPROPRIATE FOR TODAY WITH
VERY LIGHT QPF AMOUNTS. 500 MB HEIGHTS RISE ABOVE 5800M THIS
AFTERNOON WITH LIGHT WLY ONSHORE FLOW. CLOUDS WILL MITIGATE HIGH
TEMPERATURES A BIT BUT SHOULD STILL WARM 2-3 DEGREES OVER
YESTERDAY...REACHING THE LOW 80S AROUND PUGET SOUND.

MODELS CONTINUE TO ADVERTISE A SHIFT IN THE FOUR CORNERS
HIGH...BECOMING CENTERED OVER THE GREAT BASIN AND BUILDING NWD OVER
THE INTERIOR PAC NW STARTING THURSDAY. 500 MB HEIGHTS RISE OVER THE
REGION BUT THE FLOW ALOFT AND AT THE SURFACE REMAINS MORE WLY.
MORNING LOW CLOUDS SHOULD STAY CONFINED TO THE COAST AND STRAIT WITH
JUST PATCHY CLOUDS OVER THE INTERIOR...MAINLY SOUTH. THE AFTERNOON
SHOULD BE MOSTLY SUNNY WITH A WARMING AIR MASS. HIGHS WILL REACH THE
MID 80S...EXCEPT UPPER 80S SOUTHWEST INTERIOR. WLY FLOW MEANS THE
COAST THE COAST AND STRAIT WILL STAY COOLER IN THE LOW TO MID 70S.

THE UPPER RIDGE CONTINUES TO EXPAND...COVERING THE ENTIRE WRN US ON
FRIDAY. 500 MB HEIGHTS REACH 5920M FRIDAY AFTERNOON OVER THE PAC NW
BUT MODELS KEEP THE THERMALLY INDUCED TROUGH CENTERED OVER WRN
OREGON NE INTO ERN WA. THE LIGHT NW FLOW OVER WRN WA WILL INHIBIT
POTENTIAL HIGHS A BIT FOR LOCATIONS NEAR THE WATER. BUT LOW 90S ARE
A GOOD BET OVER INLAND SPOTS LIKE THE SW INTERIOR/EAST PUGET SOUND
LOWLANDS/FOOTHILLS. ELSEWHERE...EXPECT MID TO UPPER 80S EXCEPT
COOLER NEAR THE COAST AND STRAIT. THE TREND OF HOT TEMPERATURES WILL
CONTINUE TO RAMP UP THROUGH THE WEEKEND. A SPECIAL WEATHER STATEMENT
IS ALREADY IN AFFECT TO ADDRESS THE UPCOMING STRETCH OF EXCESSIVELY
HOT WEATHER. MERCER

.LONG TERM...FROM PREVIOUS DISCUSSION...THE STRONG UPPER LEVEL RIDGE
WILL SHIFT SLIGHTLY E OVER THE ID PANHANDLE THIS WEEKEND. IT WILL
GAIN A LITTLE MORE AMPLITUDE BUT 500 MB HEIGHTS WILL REMAIN ABOUT
THE SAME OVER W WA. SATURDAY LOOKS LIKE THE HOTTEST DAY OVER W WA
WITH MAX TEMPS IN THE LOWER TO MID 90S AROUND PUGET SOUND AND THE SW
INTERIOR. THE SHIFT OF THE RIDGE AXIS OVER ID WILL ALLOW S FLOW
ALOFT TO DEVELOP ALONG THE W COAST FROM CA UP THROUGH OREGON AND
OVER WA. THE GFS...ECMWF AND CANADIAN MODELS ALL CONTINUE TO SHOW
MID AND HIGH LEVEL MOISTURE BEING ADVECTED NORTHWARD OVER W WA
SATURDAY NIGHT THROUGH SUNDAY NIGHT. WITH THE POTENTIALLY UNSTABLE
HOT DRY AIR MASS IN PLACE OVER THE REGION THE ONLY FACTOR
UNACCOUNTED FOR IS AN UPPER LEVEL SHORTWAVE TROUGH TO RELEASE THE
INSTABILITY AND TRIGGER ELEVATED CONVECTION. THE MODELS HAVE BEEN
INCONSISTENT SO FAR IN SHOWING A TRIGGERING SHORTWAVE TROUGH...BUT
WITH THE HOT AIR MASS IN PLACE AND FAIRLY GOOD MODEL AGREEMENT ON
MOISTURE THERE IS AT LEAST A CHANCE FOR HIGH-BASED MAINLY DRY
THUNDERSTORMS TO DEVELOP. THIS IS ESPECIALLY SIGNIFICANT SINCE THIS
PATTERN IS A CLASSIC BUT UNDEPENDABLE PRODUCER OF FREQUENT
LIGHTNING. COMBINED WITH THE DRY WEATHER WE HAVE HAD THE PAST COUPLE
OF MONTHS...THE WILDFIRE POTENTIAL WILL BE ABOVE NORMAL.

MODELS BRING A BETTER DEFINED SHORTWAVE TROUGH ACROSS THE AREA
MONDAY...FOLLOWED BY W-SW FLOW ALOFT...ENDING THE THREAT OF
CONVECTION. KAM

&&

.CLIMATE...THE RECORD HIGH TEMPERATURE FOR SATURDAY JUNE 27TH AT
SEA-TAC AIRPORT IS 88 DEGREES...SET IN 2000. THE CURRENT FORECAST
CALLS FOR 92 DEGREES...WHICH WOULD BREAK THAT RECORD. OVER SOUTH
PUGET SOUND...THE SATURDAY RECORD HIGH FOR OLYMPIA STANDS AT 91
DEGREES SET IN 2000 AS WELL. THE CURRENT FORECAST FOR OLYMPIA IS
THREE DEGREES ABOVE THE RECORD AT 94. IN BELLINGHAM...THE SATURDAY
RECORD IS 82 DEGREES...TIED WITH THE CURRENT FORECAST.

ON A MORE SUBSTANTIAL NOTE...THE RECORD FOR THE ENTIRE MONTH OF JUNE
IN TERMS OF AVERAGE HIGH TEMPERATURES AT SEA-TAC IS 75.8 DEGREES SET
IN 1992. WITH THE FIRST PART OF JUNE HAVING ABOVE NORMAL HIGH TEMPS
ALREADY...WE ARE ON TRACK TO SHATTER THIS RECORD WITH THE FORECASTED
HEAT WAVE. JSMITH

&&

.AVIATION...A WEAK FRONT WILL CLIP THE COAST TODAY FOR LIGHT
SHOWERS. EXPECT MAINLY SCT/BKN MID AND HIGH LEVEL CLOUDS INLAND. THE
FLOW ALOFT IS WESTERLY. VFR CONDITIONS WILL PREVAIL. MARINE LAYER
LOW LEVEL CLOUDS WILL REACH THE COAST LATE TODAY. THE AIR MASS WILL
REMAIN STABLE. 33

KSEA...MID/HIGH LEVEL CLOUDS ARE EXPECTED THROUGH TONIGHT. LIGHT AND
VARIABLE WIND AT THE SURFACE BECOMING LIGHT NW IN THE AFTERNOON. 33

&&

.MARINE...A WEAK FRONT WILL BREAK UP AS IT REACHES THE COAST TODAY.
ONSHORE FLOW WILL PREVAIL WITH BORDERLINE SMALL CRAFT ADVISORY WINDS
THROUGH THE STRAIT OF JUAN DE FUCA DURING THE AFTERNOON AND EVENING
HOURS.

THERMALLY INDUCED LOW PRESSURE WILL DEVELOP OVER THE REGION FOR THE
END OF THE WEEK. THIS WILL RESULT IN A LITTLE STRONGER NORTHERLY
WINDS OVER THE COASTAL WATERS. ONSHORE FLOW WILL CONTINUE EARLY NEXT
WEEK WITH LOW PRES OVER EASTERN WA. 33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY CENTRAL AND EAST STRAIT OF JUAN DE FUCA.

&&

$$

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










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