Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 281552
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
855 AM PDT TUE JUL 28 2015

.SYNOPSIS...AN UPPER LEVEL RIDGE WILL BUILD OVER THE PACIFIC
NORTHWEST TODAY THROUGH FRIDAY. THE UPPER RIDGE MAY PERSIST INTO
NEXT WEEKEND. EXPECT SUNNY DAYS AND A WARMING TREND THROUGH
THURSDAY. WARM TO HOT TEMPERATURES WILL LIKELY PERSIST ACROSS THE
REGION INTO NEXT WEEKEND.

&&

.SHORT TERM...500 MB HEIGHTS ACROSS THE REGION ARE GRADUALLY RISING
AS THE MAIN UPPER RIDGE OVER THE SOUTH CENTRAL US RETROGRADES TOWARD
THE 4 CORNERS REGION OF THE SOUTHWEST. WHILE LOW LEVEL FLOW IS
EXPECTED TO REMAIN LIGHT ONSHORE OR NORTHWESTERLY...TEMPERATURES AT
850 MB RISE TO AROUND 14C THIS AFTERNOON...16C ON WED...AND 20C ON
THU AS THE 500 MB HEIGHTS RISE TO AROUND 588 DAM. BY THU AFTERNOON
THE CANADIAN...ECMWF AND NAM12 ALL SHOW WEAK THERMAL TROUGHING
EXTENDING FROM THE OLYMPICS SOUTHWARD INTO THE WILLAMETTE VALLEY
WITH THE MAIN FOCUS OF THE HEAT BUILDING INTO EASTERN WASHINGTON.
THE GFS APPEARS TO SHOW LESS THERMAL TROUGHING THAN THE OTHER
MODELS...BUT IS OTHERWISE CONSISTENT.

IN THIS PATTERN...EXPECT THE MOST WARMING -AND THE WARMEST
TEMPERATURES ON THURSDAY- TO BE IN THE INTERIOR FROM ABOUT SEATTLE
SOUTHWARD. NORTH TO NORTHWEST FLOW...WITH WESTERLY INFLOW THROUGH
THE STRAIT OF JUAN DE FUCA...WILL KEEP THE IMMEDIATE COASTAL ZONES.
AREAS ALONG THE STRAIT OF JUAN DE FUCA...AND THE INTERIOR FROM ABOUT
EVERETT NORTHWARD 6 TO 9 DEGREES COOLER THAN THE SEATTLE METRO AREA
AND THE I-5 CORRIDOR TO THE SOUTH.

CURRENT FORECASTS SHOW HIGHS AROUND 80 IN SEATTLE TODAY...IN THE MID
80S ON WED...AND NEAR 90 ON THURSDAY. WITH WARMING ALOFT AND RISING
DAYTIME TEMPERATURES...EXPECT EARLY MORNING LOWS TO FALL ONLY TO
AROUND 60 IN THE URBAN AREAS FOR THE NEXT SEVERAL DAYS.

CURRENT SHORT TERM FORECAST LOOKS GOOD AND NO MORNING UPDATE IS
NEEDED. ALBRECHT

.LONG TERM...THE QUESTION OF THE DAY FOR WESTERN WASHINGTON IS -HOW
LONG WILL THE HEAT LAST. THE CURRENT FORECAST FOLLOWS THE
OPERATIONAL GFS FROM 00Z LAST NIGHT AND 06Z EARLY THIS MORNING.
THOSE RUNS SHOWED VERY WARM TO HOT CONDITIONS PERSISTING THROUGH THE
WEEKEND AND POSSIBLY INTO EARLY NEXT WEEK.

IT APPEARS THAT THE RECENT OPERATIONAL RUNS OF THE GFS ARE ON THE
WARM SIDE OF THE ENSEMBLE SOLUTIONS WITH MOST MEMBERS FOLLOWING A
SLIGHTLY COOLER ECMWF AND CANADIAN BLEND. THE MODEL DIFFERENCES
APPEAR TO BE RELATED TO THE STRENGTH OF SHORT WAVE TROUGHS TO THE
NORTH OF THE BORDER VS THE STRENGTH OF THE RIDGE TO THE SE. THE
HISTORY OF RIDGES THIS SUMMER FAVORS THE GFS. IF THE 12Z RUNS FAVOR
THE GFS RIDGE...A HEAT OUTLOOK FOR ANOTHER STRING OF 90 DEGREE DAYS
THURSDAY THROUGH THE WEEKEND WITH WARM OVERNIGHT LOWS MAY BE NEEDED
TO BE ISSUED LATER THIS AFTERNOON. ALBRECHT

&&

.AVIATION...AN UPPER RIDGE WILL REMAIN OVER THE REGION TODAY.
CONTD NLY FLOW ALOFT AND LOW LEVEL ONSHORE FLOW. THERE WERE
LOCALIZED AREAS OF IFR CIGS/VSBYS THIS MORNING. EXPECT VFR
CONDITIONS OVER THE ENTIRE AREA BY 1900 UTC.

KSEA...VFR. WINDS WILL BE NLY.

&&

.MARINE...
HIGH PRES OFFSHORE WITH LOWER PRES E OF THE CASCADES WILL KEEP THE
FLOW ONSHORE THROUGH THU...ALTHOUGH THE FLOW WILL BECOME BRIEFLY
OFFSHORE OR NORTHERLY WED NIGHT.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...

WA...NONE.
PZ...SMALL CRAFT ADVISORY IN EFFECT CENTRAL AND EASTERN STRAIT OF JUAN DE
      FUCA TONIGHT.

&&

$$

WWW.WEATHER.GOV/SEATTLE

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


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