Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 282203
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PDT TUE JUL 28 2015

.SYNOPSIS...AN UPPER LEVEL RIDGE WILL BUILD INTO THE PACIFIC
NORTHWEST THROUGH FRIDAY BRINGING INCREASINGLY WARM TEMPERATURES TO
THE REGION. WARM TO HOT WEATHER WILL LIKELY PERSIST INTO EARLY NEXT
WEEK AS THE UPPER RIDGE REMAINS PARKED OVER THE AREA.

&&

.SHORT TERM...A STRONG AND VERY WARM UPPER LEVEL HIGH CENTERED OVER
MISSOURI THIS AFTERNOON IS FORECAST BY ALL OF THE GLOBAL MODELS TO
RETROGRADE TO AROUND THE FOUR CORNERS AREA OF THE DESERT SOUTHWEST
BY FRIDAY OR FRIDAY NIGHT. 500 MB HEIGHTS IN THE PACIFIC NORTHWEST
WILL RESPOND TO THE BUILDING RIDGE TO OUR SOUTHEAST RISING TO AROUND
588 DAM THU INTO FRI. IN RESPONSE TO THE WARMING AND SUBSIDENCE
ALOFT...850 MB TEMPERATURES WILL RISE TO AROUND 16C WED AFTERNOON
AND TO AROUND 20C THU AFTERNOON. THE NAM12...ECMWF AND CANADIAN
SOLUTIONS CONTINUE TO SHOW THE DEVELOPMENT OF A WEAK THERMAL TROUGH
FROM THE OLYMPICS S INTO THE WILLAMETTE VALLEY OF CENTRAL OREGION IN
RESPONSE TO THE RIDGING ALOFT. BY THU AFTERNOON TEMPERATURES IN THE
INTERIOR FROM ABOUT SEATTLE SOUTHWARD WILL RISE TO AROUND THE 90
DEGREE MARK...WITH SOME AREAS IN THE SOUTH INTERIOR ALONG THE I-5
CORRIDOR REACHING THE MID 90S.

THE 18Z NAM12 SHOWS SOME MARINE AIR MAKING IT INTO THE CHEHALIS GAP
AND ONTO THE COAST FRI OR NIGHT. BUT WITH THERMAL TROUGHING
REMAINING FROM THE OLYMPICS SE INTO THE SOUTH WASHINGTON
CASCADES...THE SEATTLE METRO AREA AND MOST OF THE SOUTH INTERIOR
WILL CONTINUE TO SEE HOT CONDITIONS. THE WEAK INFLUX OF MARINE
MOISTURE THU NIGHT INTO FRI MAY DO LITTLE MORE THAN RAISE DEWPOINT
TEMPERATURES INTO THE MID 50S...MAKING IT FEEL MORE UNCOMFORTABLE.

IN RESPONSE TO THE MODELS CONVERGING TOWARD A WARMER SOLUTION
THROUGH AT LEAST FRIDAY AND LIKELY THROUGH THE WEEKEND...A SPECIAL
WEATHER STATEMENT FOR EXPECTED HOT TEMPERATURES WILL BE ISSUED FOR
THE INTERIOR WITH THE AFTERNOON FORECAST PACKAGE. ALBRECHT

.LONG TERM...THE 12Z FORECAST MODELS APPEAR TO BE CONVERGING ON A
WARMER SOLUTION..SIMILAR TO WHAT WAS ADVERTISED BY THE 00Z AND 06Z
RUNS OF YESTERDAY AND LAST NIGHT. THE GFS ENSEMBLE MEAN FROM THE 12Z
RUN HAS ALSO WARMED TOWARD THE OPERATIONAL RUN. THIS MAKES IT MORE
LIKELY THAT THE HOT AND INCREASINGLY HUMID CONDITIONS THAT WE WILL
SEE ON FRIDAY WILL PERSIST THROUGH AT LEAST SUNDAY AND POSSIBLY INTO
EARLY NEXT WEEK. IT APPEARS INCREASINGLY LIKELY THAT SEATAC AIRPORT
WILL BREAK THE OLD RECORD OF 9 90 DEGREES IN A CALENDAR YEAR THAT
OCCURRED IN 1958. ALBRECHT

&&

.AVIATION...AN UPPER RIDGE WILL REMAIN OVER THE REGION THRU
TONIGHT...ALTHOUGH IT WILL WEAKEN SOME. NLY FLOW ALOFT WILL BECOME
WLY OVERNIGHT. CONTD LOW LEVEL ONSHORE FLOW. WEAKENING OF THE RIDGE
MIGHT RESULT IN A BIT MORE STRATUS AND/OR FOG /MAINLY IFR/ WED
MORNING...PARTICULARLY OVER THE COAST.

KSEA...VFR. WINDS WILL REMAIN NLY.

&&

.MARINE... HIGH PRES OFFSHORE WITH LOWER PRES E OF THE CASCADES WILL
KEEP THE FLOW ONSHORE THROUGH FRI. ANTICIPATE THE FLOW TO BECOME
BRIEFLY NORTHERLY OR OFFSHORE WED AND THU NIGHTS DUE TO A THERMALLY
INDUCED AREA OF LOW PRES TRYING TO SET UP ALONG THE WASHINGTON COAST.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...

WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TIL 3 AM
 WEDNESDAY FOR THE CENTRAL AND EASTERN STRAIT OF JUAN DE
 FUCA.

&&

$$

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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