Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 291555
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT WED JUL 29 2015

.SYNOPSIS...AN UPPER RIDGE WILL KEEP DRY AND VERY WARM CONDITIONS
OVER THE AREA THROUGH THE WEEKEND. WARM TO HOT WEATHER MAY PERSIST
INTO EARLY NEXT WEEK AS THE UPPER RIDGE REMAINS ANCHORED OVER THE
WESTERN US.

&&

.SHORT TERM...THE CENTER OF A STRONG AND WARM UPPER LEVEL RIDGE OVER
THE SOUTH-CENTRAL UNITED STATES WILL RETROGRADE TO THE FOUR-CORNERS
REGION OF THE DESERT SOUTHWEST TODAY THROUGH FRIDAY WHILE IT EXPANDS
ACROSS THE WEST. FLOW ALOFT IS LIGHT ONSHORE WHILE LOW LEVEL FLOW IS
LIGHT NORTH TO NORTHWEST.

IN THIS PATTERN THE SHORT TERM MODELS SEEM TO DO A GOOD JOB IN
DEVELOPING A WEAK THERMAL TROUGH FROM THE OLYMPICS SOUTH-SOUTHEAST
THROUGH THE SOUTH INTERIOR AND INTO THE WILLAMETTE VALLEY OF OREGON.
AS THE SURFACE PATTERN DEVELOPS...850 MB TEMPERATURES WARM TO AROUND
17C THIS AFTERNOON AND TO AROUND 20C THURSDAY THROUGH FRIDAY
AFTERNOONS. WITH THE AXIS OF THE THERMAL TROUGH INLAND...EXPECT THE
COAST AWAY FROM THE BEACHES TO GET WARM...BUT NOT HOT. AREAS NEAR
THE WATER NORTH OF SEATTLE AND IN THE NORTH INTERIOR WILL BE COOLED
BY THE 10 TO 20 KT NORTH TO NORTHWEST BREEZES KEEPING HIGHS IN THE
70S TO LOWER 80S. THE SEATTLE METRO AREA SOUTHWARD IN THE INTERIOR
VALLEYS WILL WARM TO THE MID 80S TO LOWER 90S TODAY WITH HIGHEST
TEMPERATURES AROUND 00Z THIS AFTERNOON.

DEWPOINT TEMPERATURES AROUND 50 DEGREES ALONG WITH THE BREEZE WILL
KEEP THINGS FROM FEELING OVERLY OPPRESSIVE OUTDOORS TODAY.
RADIATIONAL COOLING WITH THE DRIER AIR WILL ALLOW TEMPERATURES
TONIGHT TO FALL INTO THE 50S MOST AREAS...WHILE THE WARMER URBAN
HEAT ISLAND AREAS OF SEATTLE AND TACOMA STAY CLOSE TO THE 60 DEGREE
MARK TONIGHT.

WITH THE WARMER TEMPERATURES ALOFT ON THURSDAY...EXPECT HIGHS TO BE
ABOUT 3-4 DEGREES HOTTER WITH MOST AREAS FROM SEATTLE SOUTHWARD IN
THE INTERIOR REACHING INTO THE LOWER TO MID 90S. AREAS AWAY FROM THE
WATER NEAR THE CASCADES NORTH OF SEATTLE WILL ALSO SEE HOT
TEMPERATURES ON THURSDAY. NIGHTTIME TEMPERATURES THURSDAY NIGHT WILL
RISE 2-3 DEGREES WITH THE HOTTER START. WITH THE FORECAST WARMTH FOR
THURSDAY AND FRIDAY...WILL LIKELY ISSUE A HEAT ADVISORY FOR THE
SEATTLE-TACOMA URBAN AREAS FOR THURSDAY THROUGH FRIDAY EVENING WITH
THE AFTERNOON PACKAGE TODAY. FRIDAY HIGH TEMPERATURES WILL MAY EVEN
BE A COUPLE DEGREES HOTTER THAN THURSDAY.

AT THIS POINT THE CURRENT SHORT TERM FORECAST APPEARS TO BE IN GOOD
SHAPE. NO UPDATE IS PLANNED THIS MORNING. ALBRECHT

.LONG TERM...WHILE THE FOUR CORNERS HIGH REMAINS IN PLACE SATURDAY
THROUGH EARLY NEXT WEEK...UPPER LEVEL HEIGHTS OVER THE PACIFIC
NORTHWEST START A DOWNWARD TREND ON SATURDAY. THE 06Z GFS ALONG WITH
THE 00Z ECMWF AND 00Z CANADIAN HAVE REVERTED BACK TO COOLER
SOLUTIONS STARTING SUNDAY NIGHT AS AN UPPER LEVEL LOW PRESSURE
SYSTEM WEST OF JUNEAU SHIFTS SOUTHEAST TOWARD SOUTHWESTERN BRITISH
COLUMBIA BY THE MIDDLE OF NEXT WEEK. MOST EXTENDED MODEL SOLUTIONS
NOW SHOW GRADUAL COOLING SATURDAY AND SUNDAY FOLLOWED BY RATHER
SIGNIFICANT ONSHORE FLOW EARLY NEXT WEEK AND EVEN AN CHANCE OF
SHOWERS BY NEXT WEDNESDAY. THE CURRENT EXTENDED FORECAST FOLLOWS
OLDER SOLUTIONS THAT ALLOWED THE SOUTHWESTERN RIDGE TO DOMINATE THE
CIRCULATION OVER THE AREA. CONFIDENCE IN THE LONG TERM FORECAST IS
RATHER LOW TODAY AND SOME CHANGES MAY NEED TO BE MADE WITH THE
EXTENDED FORECAST IN THE AFTERNOON PACKAGE IF THE NEWER 12Z
SOLUTIONS SHOW A MORE DOMINATE INFLUENCE OF THE NORTHERN STREAM
UPPER LOW ON THE LOCAL WIND PATTERN. ALBRECHT

&&

.CLIMATE...ON THIS DATE BACK IN 2009 THE WARMEST DAY ON RECORD IN
SEATTLE OCCURRED WITH A HIGH OF 103 DEGREES. IN ADDITION TO BEING
THE WARMEST DAY ON RECORD JULY 29TH IS ALSO THE DRIEST DAY ON RECORD
AT SEATTLE-TACOMA AIRPORT. SINCE RECORDS STARTED IN 1945 THERE HAS
BEEN A TOTAL OF JUST 0.31 INCHES OF RAIN RECORDED ON THIS DAY.
MEASURABLE RAIN HAS OCCURRED ONLY 4 TIMES ( 0.17 INCHES 1993, 0.11
INCHES 2008, 0.02 INCHES 1955 AND 0.01 INCHES IN 1981 ). FELTON

&&

.AVIATION...AN UPPER RIDGE WILL REMAIN OVER THE REGION. CONTD WLY
FLOW ALOFT. LOW LEVEL NLY FLOW WILL BECOME NWLY THIS AFTERNOON.
PATCHY LIFR CIGS/VSBYS ON THE COAST WILL DISSIPATE BY 1800 UTC.

KSEA...VFR. WINDS WILL REMAIN NLY...POSSIBLY GUSTING TO NEAR 20
KT THIS AFTERNOON.

&&

.MARINE...
HIGH PRES OFFSHORE WITH LOWER PRES E OF THE CASCADES WILL KEEP THE
FLOW ONSHORE OR NORTHWESTERLY THROUGH THIS WEEKEND. THERE IS A
POSSIBILITY THAT WIND SPEEDS COULD REACH ADVISORY CRITERION OVER
THE ADMIRALTY INLET AND PUGET SOUND THIS AFTERNOON.

THE FLOW WILL BECOME BRIEFLY NORTHERLY OR OFFSHORE EARLY THU AND
FRI MORNINGS 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 IN EFFECT FROM 5 PM THIS AFTERNOON TIL
 11 PM TONIGHT FOR THE COASTAL WATERS FROM JAMES ISLAND TO
 CAPE SHOALWATER OUT TO 10 NM.

&&

$$

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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