Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 011053
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
350 AM PDT SAT AUG 1 2015

.SYNOPSIS...AN UPPER RIDGE WILL GRADUALLY WEAKEN OVER THE NEXT
COUPLE OF DAYS. ONSHORE FLOW WILL RETURN EARLY NEXT WEEK FOR
COOLER WEATHER. AN UPPER TROUGH WILL BRING A CHANCE OF SHOWERS
LATER IN THE WEEK.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS LOW CLOUDS ALONG THE COAST
WITH CLEAR SKIES OVER THE REMAINDER OF THE AREA AT 3 AM. WITH THE
CLEAR SKIES OVER MOST OF THE AREA TEMPERATURES WERE IN A WIDE RANGE
AT 3 AM...LOWER 50S TO LOWER 70S.

UPPER LEVEL RIDGE REMAINING OVER THE AREA TODAY RESULTING IN ANOTHER
HOT DAY FOR THE INTERIOR. SURFACE GRADIENTS ARE FLAT AND
TEMPERATURES ALOFT ARE SIMILAR TO FRIDAY`S READINGS. TEMPERATURE
GUIDANCE IS GOING FOR A FEW DEGREES OF COOLING TODAY BUT WITH LITTLE
CHANGE IN THE PATTERN WILL GO MORE ALONG THE LINES OF PERSISTENCE
FOR HIGHS TODAY WITH THE WARMEST LOCATIONS ONCE AGAIN IN THE MID TO
UPPER 90S AND THE COOL SPOT BEING THE COAST WITH 70S AND LOWER 80S.

SOME SMALL CHANGES BEGIN TO TAKE PLACE TONIGHT INTO SUNDAY. THE
UPPER LEVEL RIDGE BEGINS TO WEAKEN AND SHIFT EAST. BY 00Z MONDAY THE
THERMALLY INDUCED SURFACE TROUGH IS OVER EASTERN WASHINGTON. THIS
WILL INDUCE SOME LOW LEVEL ONSHORE FLOW IN WESTERN WASHINGTON SUNDAY
AFTERNOON. TEMPERATURES ALOFT COOL SLIGHTLY...850 MB TEMPERATURES
LOWERING FROM NEAR PLUS 20C TO NEAR PLUS 18C. THE COMBINATION OF
THESE TWO VARIABLES WILL BE SLIGHTLY LOWER MAX TEMPERATURES ON
SUNDAY...BUT STILL PLENTY WARM WITH LOWER 90S FROM SEATTLE
SOUTHWARD. 80S WILL BE COMMON NORTH OF SEATTLE WITH 70S ALONG THE
COAST. EVEN WITH THE SLIGHTLY COOLER TEMPERATURES THE HEAT ADVISORY
WILL REMAIN UP THROUGH SUNDAY EVENING FOR THE SEATTLE
AREA...SOUTHWEST INTERIOR AND EAST PUGET SOUND LOWLANDS.

WITH THE UPPER LEVEL RIDGE AXIS AND THERMALLY INDUCED SURFACE TROUGH
EAST OF THE AREA SUNDAY NIGHT A MARINE PUSH WILL DEVELOP OVER
WESTERN WASHINGTON. MODEL ONSHORE GRADIENTS ARE NOT VERY IMPRESSIVE
AND INDICATING MORE OF A WEAK PUSH INTO MONDAY. TEMPERATURES ALOFT
CONTINUE TO COOL...850 MB TEMPERATURES DOWN AROUND PLUS 14 OR 15C BY
00Z TUESDAY...AS A WEAK UPPER LEVEL TROUGH MOVES INTO THE AREA.
MODEL CROSS SECTIONS ALSO SHOW THE WINDS RIGHT OFF THE GROUND UP
THROUGH 700 MB REMAINING NORTHWESTERLY SUNDAY NIGHT INTO MONDAY.
THIS ALSO SUPPORTS THE WEAK PUSH SCENARIO. IN GENERAL WILL GO FOR 5
TO 10 DEGREES OF COOLING ON MONDAY VERSUS SUNDAYS MAX TEMPERATURE
READINGS. THIS WILL PUT MAX TEMPERATURES IN THE INTERIOR MOSTLY IN
THE 70S TO LOWER 80S. WITH 60S AND LOWER 70S ALONG THE COAST.

MORE SIGNIFICANT COOLING ON MONDAY WITH THE UPPER LEVEL RIDGE AXIS
AND THERMALLY INDUCED THERMAL SURFACE TROUGH TO THE EAST. TROUGH IS
TWO VARIABLES WILL RE

.LONG TERM...IF YOU ARE NOT A FAN OF THE HOT WEATHER WE HAVE BEEN
EXPERIENCING THE LAST FEW DAYS THEN YOU WILL LIKE THE EXTENDED
FORECAST. WHILE THERE IS NOT A LOT OF CONSISTENCY IN THE MODELS THE
GENERAL IDEA OF COOLER WEATHER IS EVIDENT IN ALL OF THE EXTENDED
SOLUTIONS. THE ECMWF IS THE MORE OPTIMISTIC OF THE MODELS WITH
NORTHWESTERLY FLOW ALOFT OVER THE AREA UNTIL A WEAK RIDGE BUILDS
LATE IN THE WEEK. THE GFS AND CANADIAN BRING AN UPPER LEVEL LOW DOWN
FROM THE NORTHWEST AND MOVE THE LOW INTO SOUTHERN BRITISH
COLUMBIA/WESTERN WASHINGTON THURSDAY WITH THE CANADIAN MODEL ABOUT
12 HOURS SLOWER WITH THIS FEATURE VERSUS THE GFS. THE CANADIAN KEEPS
SOME WEAK TROFINESS OVER THE AREA FRIDAY WHILE THE GFS DOES SHOW
SOME WEAK RIDGE BY LATER FRIDAY INTO SATURDAY. EVEN THROUGH IT IS
THE CLIMATOLOGICALLY DRIEST TIME OF THE YEAR WITH THE LACK OF
CONSENSUS IN THE MODELS WILL STAY WITH THE CURRENT FORECAST THAT HAS
A CHANCE OF SHOWERS FORECAST FOR MOST OF THE AREA THURSDAY AND
FRIDAY WITH HIGH TEMPERATURES NEAR OR A LITTLE BELOW NORMAL...IN THE
70S FOR THE INTERIOR AND 60S FOR THE COAST. FELTON

&&

.CLIMATE...JULY ENDED UP BEING THE WARMEST MONTH ON RECORD IN
SEATTLE WITH AN AVERAGE TEMPERATURE OF 71.2 DEGREES. THE OLD RECORD
WAS 71.1 DEGREES SET IN AUGUST OF 1967. THIS RECORD INCLUDES THE
FEDERAL BUILDING RECORDS WHICH GO BACK TO THE 1890`S.

IT WAS THE WARMEST JULY ON RECORD AT BOTH HOQUIAM AND FORKS. AT
HOQUIAM THE AVERAGE TEMPERATURE FOR JULY WAS 63.9 DEGREES BREAKING
THE RECORD OF 63.0 DEGREES SET IN 1958. AT FORKS THE AVERAGE
TEMPERATURE WAS 63.0 DEGREES BREAKING THE RECORD OF 61.4 SET IN
1990. RECORDS BEGAN IN HOQUIAM IN 1953 AND AT FORKS IN 1966.

OTHER LOCATIONS AROUND WESTERN WASHINGTON...AT BELLINGHAM IT WAS THE
2ND WARMEST JULY ON RECORD WITH AN AVERAGE TEMPERATURE OF 67.2. THE
RECORD IS 68.0 DEGREES SET IN 1958. OLYMPIA ALSO HAD THE SECOND
WARMEST JULY ON RECORD WITH AN AVERAGE TEMPERATURE OF 68.0 DEGREES.
THE RECORD IS 69.1 SET ALSO IN 1958.

&&

.AVIATION...A BROAD UPPER LEVEL RIDGE WILL REMAIN OVER THE PACIFIC
NORTHWEST THROUGH THIS WEEKEND WITH LIGHT W-SW FLOW ALOFT. EXCEPT
FOR AREAS OF LATE NIGHT AND MORNING STRATUS...THE AIR MASS WILL
REMAIN DRY...STABLE AND VERY WARM. THE DENSITY ALTITUDE WILL BE
HIGHER THAN NORMAL DURING THE AFTERNOON HOURS.

AREAS OF IFR STRATUS HAVE FORMED ALONG THE COAST...OVER THE WESTERN
STRAIT OF JUAN DE FUCA AND BETWEEN KHQM AND KSHN. THE STRATUS SHOULD
BURN OFF AGAIN BY 18Z THIS. OTHERWISE CLEAR SKIES WILL CONTINUE
ACROSS W WA.

KSEA...CLEAR SKIES FOR GOOD VFR CONDITIONS. SURFACE WINDS WILL
REMAIN N 3-7 KT THIS MORNING THEN RISE TO N-NW 5-10 KT AFTER 18Z
SATURDAY. KAM

&&

.MARINE...A LARGE SURFACE RIDGE OFFSHORE WILL COMBINE WITH LOWER
PRESSURE OVER E WA TO MAINTAIN VARYING DEGREES OF ONSHORE FLOW
THROUGH NEXT WEEK. THE ONSHORE FLOW IS EXPECTED TO BE MAINLY
MODERATE DURING THE LATE AFTERNOON AND EVENING HOURS THIS
WEEKEND...BUT STRONG FLOW WITH POSSIBLE GALES IN THE STRAIT OF JUAN
DE FUCA IS POSSIBLE.

EARLIER MODELS SUGGESTED GALES IN THE CENTRAL AND EAST STRAIT THIS
EVENING...BUT THE 00Z GFS HAS BACKED OFF ON THE UIL-BLI PRESSURE
GRADIENT. NONE OF THE U.S. MESOSCALE MODELS ARE CLOSE TO GALE FORCE
WINDS...AND BOTH THE 18Z AND 00Z 2.5KM CANADIAN LAM MODEL ONLY
SHOWED A TINY AREA OF 30-35 KT WINDS FOR JUST ONE HOUR. AS A RESULT
I HAVE CONVERTED THE GALE WATCH TO A HIGH END SCA FOR LATE THIS
AFTERNOON AND TONIGHT. A SCA WILL ALSO CONTINUE OVER THE OUTER
COASTAL WATERS FOR BORDERLINE SCA NW WINDS A TIMES. THIS NW FLOW ON
THE COAST IS EXPECTED TO SPREAD OVER THE INNER COASTAL WATERS ALONG
THE CENTRAL COAST THIS EVENING. KAM

&&

.FIRE WEATHER...PREVIOUS DISCUSSION...A CRITICAL PERIOD FOR FIRE
WEATHER CONTINUES OVER ALL OF WESTERN WASHINGTON...WITH A VERY DRY
AIR MASS IN PLACE. THE IMMEDIATE COAST HAS SEEN SOME RELIEF THIS
AFTERNOON FROM SEA BREEZES WHICH HAVE RAISED DEWPOINTS INTO THE
UPPER 50S AT HOQUIAM AND QUILLAYUTE. ELSEWHERE ACROSS WESTERN
WASHINGTON...DRY AIR PERSISTS.

IN ADDITION...ELEVATED MOUNTAIN LOCATIONS ARE FEELING THE ADDED
EFFECT OF SOMEWHAT UNSTABLE MID-LEVEL AIR...WITH BOTH MID-LEVEL AND
HIGH-LEVEL HAINES 5 CONDITIONS CONTINUING THROUGH SATURDAY EVENING.
VISIBLE SATELLITE IMAGERY SHOWED A BURST OF SMOKE THIS AFTERNOON
COMING FROM THE PARADISE FIRE...SO IT APPEARS THE FIRE IS FEELING
THE EFFECTS OF THE DRY AND UNSTABLE AIR MASS. WILL KEEP THE RED FLAG
WARNING GOING FOR ELEVATIONS ABOVE 2000 FEET UNTIL SATURDAY EVENING
FOR THE DRY AND UNSTABLE AIR MAS. LARGE FIRE GROWTH IN WESTERN
WASHINGTON HISTORICALLY TAKES PLACE UNDER SUCH CONDITIONS. HANER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...HEAT ADVISORY REMAINS IN EFFECT TIL 8 PM SUNDAY FOR PARTS OF
THE PUGET SOUND REGION AND SOUTHWEST INTERIOR.

RED FLAG WARNING IN EFFECT TIL 10 PM SATURDAY NIGHT FOR THE
CASCADES AND OLYMPICS ABOVE 2000 FEET.

PZ...SMALL CRAFT ADVISORY OUTER COASTAL WATERS AND CENTRAL AND EAST
    STRAIT OF JUAN DE FUCA.

&&

$$

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


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