Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 280448
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
945 PM PDT WED AUG 27 2014

.SYNOPSIS...THE MARINE LAYER WILL DEEPEN TONIGHT AND A SMALL UPPER
TROUGH WILL MOVE THROUGH AREA THURSDAY FOR CLOUDIER COOLER WEATHER.
ANOTHER LARGER UPPER TROUGH WILL BRING A CHANCE OF SHOWERS FRIDAY
THROUGH THIS WEEKEND. MONDAY NIGHT AND TUESDAY COULD SEE BRIEF
IMPROVEMENT BEFORE ANOTHER UPPER TROUGH MOVES THROUGH TOWARDS THE
MIDDLE OF NEXT WEEK.

&&

.SHORT TERM...THE MAIN STORY WEATHER STORY TONIGHT IS THE WARM
WEATHER WESTERN WASHINGTON HAS BEEN EXPERIENCING HAS COME TO AN
END...AT LEAST FOR A FEW DAYS. THE MARINE PUSH IS ON TONIGHT WITH
THE KUIL-KBLI GRADIENT OVER PLUS 3 MB AND RISING THE KHQM-KSEA IS
AROUND 2 MB. SATELLITE IMAGERY AT 04Z SHOWS THE STRATUS STILL
CONFINED TO THE COAST BUT WITH THE INCREASING ONSHORE FLOW OVERNIGHT
THE STRATUS WILL SPREAD INLAND AS WELL AS FORM IN PLACE LATE
TONIGHT/EARLY THURSDAY MORNING. BY SUNRISE STRATUS SHOULD COVER MOST
OF THE LOWLANDS WESTERN WASHINGTON. WITH THE INCREASING CLOUD COVER
LOWS TEMPERATURES TONIGHT WILL STAY IN THE 50S AND LOWER 60S.

COOLER AND CLOUDIER WEATHER IN STORE FOR THURSDAY. WEAK UPPER LEVEL
TROUGH ARRIVING ALONG THE COAST IN THE MORNING WHICH COULD PROVIDE
ENOUGH LIFT TO SQUEEZE A LITTLE DRIZZLE OUT FOR THE COAST. THE
TROUGH WILL MOVE THROUGH THE INTERIOR IN THE AFTERNOON. 500 MB
HEIGHTS REMAINING IN THE MID TO UPPER 570 DECAMETERS SO NOT
EXPECTING ANY PRECIPITATION OVER THE INTERIOR BUT THE TROUGH WILL
HELP KEEP THE MARINE LAYER SOMEWHAT INTACT. CURRENT FORECAST IS
MOSTLY CLOUDY FOR THE INTERIOR AND WILL STAY WITH THAT WORDING.
HIGHS WILL BE MUCH COOLER OVER THE INTERIOR...10 TO 15 DEGREES
COOLER THAN TODAY...UPPER 60S TO MID 70S. THE COAST WILL REMAIN IN
THE 60S AGAIN.

NOT MUCH GOING ON THURSDAY NIGHT WITH LOW LEVEL ONSHORE FLOW AND THE
NEXT TROUGH TO REACH THE AREA STILL BACK NEAR 130W AT 12Z/5AM FRIDAY
MORNING. WITH THE LOW LEVEL ONSHORE FLOW THERE WILL STILL BE PLENTY
OF CLOUD COVER. LOW TEMPERATURES IN THE 50S WILL BE COMMON.

LOW LEVEL ONSHORE FLOW PATTERN CONTINUING ON FRIDAY WITH A STRONGER
THAN THURSDAY...BUT STILL NOT VERY STRONG...UPPER LEVEL TROUGH
ARRIVING FRIDAY AFTERNOON. THE TROUGH IS STRONG ENOUGH FOR A CHANCE
OF SHOWERS ACROSS THE AREA. THE AFTERNOON ARRIVAL OF THE TROUGH WILL
MAKE IT HARD FOR MUCH DAYTIME WARMING ACROSS THE AREA. SEATTLES
STREAK OF CONSECUTIVE DAYS WITH HIGHS 70 PLUS...CURRENTLY AT 34 DAYS
INCLUDING TODAY...WILL BE IN JEOPARDY WITH HIGHS OVER THE INTERIOR
IN THE MID 60S TO LOWER 70S.

LITTLE CHANGE IN THE PATTERN FRIDAY NIGHT AND SATURDAY WITH LOW
LEVEL ONSHORE FLOW AND YET ANOTHER TROUGH ARRIVING ON SATURDAY
KEEPING THE MOSTLY CLOUDY AND COOL WITH A CHANCE OF SHOWERS FORECAST
INTACT. CURRENT FORECAST HAS THE TRENDS COVERED. NO UPDATE THIS
EVENING. FELTON

.LONG TERM...PREVIOUS DISCUSSION FOLLOWS. SHOWERS WILL BEGIN TO
TAPER OFF SATURDAY NIGHT INTO SUNDAY...BUT A SERIES OF SMALL
DISTURBANCES MOVING THROUGH THE AREA MEANS THAT THE THREAT OF
SHOWERS...MOSTLY CONFINED TO THE MOUNTAINS...WILL CONTINUE THROUGH
MONDAY. IN THE MOST RECENT RUNS...THE ECMWF AND GFS ARE BOTH
AGREEING THAT THERE WILL BE A BRIEF LULL IN THE SHOWERS AND POSSIBLY
PARTLY SUNNY SKIES MONDAY NIGHT INTO TUESDAY. HOWEVER...THEY ALSO
SUGGEST THAT ANOTHER SYSTEM WILL MOVE INTO THE AREA TUESDAY NIGHT OR
WEDNESDAY...BRINGING POSSIBLE WIDESPREAD SHOWERS. JSMITH

&&

.CLIMATE...WITH A HIGH OF 84 DEGREES TODAY THIS WAS THE 34TH DAY IN
JULY AND AUGUST WITH A HIGH OF 80 PLUS IN SEATTLE. THIS IS THE MOST
EVER FOR THE TWO MONTH PERIOD. THE PREVIOUS RECORD WAS 33 DAYS IN
1958 AND 1985.

TODAY WAS THE 39TH DAY THIS YEAR WITH A HIGH OF 80 PLUS IN SEATTLE.
THERE HAVE ONLY BEEN 5 YEARS WITH 40 OR MORE DAYS IN THE YEAR WITH
HIGHS 80 PLUS...1958 47 DAYS...1967 46 DAYS...1961 45 DAYS...1987
AND 2013...40 DAYS. FELTON

&&

.AVIATION...CLOUDS WILL INCREASE ACROSS WESTERN WA TONIGHT AS A WEAK
COLD FRONT ADVANCES FROM THE NW. THE FLOW ALOFT IS WESTERLY. ONSHORE
FLOW WILL BRING LOW LEVEL STRATUS CLOUDS INLAND EARLY THU MORNING
WITH MVFR TO IFR CONDITIONS EXPECTED. THE COLD FRONT WILL CROSS
WESTERN WA THU MORNING WITH PATCHY DRIZZLE ALONG THE COAST...AND A
FEW LIGHT SHOWERS IN THE MOUNTAINS. A PSCZ MAY FORM OVER THE
KING/SNOHOMISH BORDER THU AFTERNOON FOR ISOLATED SHOWERS AS WELL.
OTHERWISE LOW LEVEL CLOUDS WILL LIFT THU AFTERNOON WITH VFR
CONDITIONS EXPECTED. 33

KSEA...A STRONGER ONSHORE PUSH TONIGHT WILL BRING MARINE CLOUDS TO
THE TERMINAL EARLY THU MORNING WITH MVFR CONDITIONS EXPECTED. LIGHT
W/NW WINDS WILL TURN SLY EARLY THU. LOW CLOUDS WILL LIFT THU
AFTERNOON FOR VFR CONDITIONS. 33

&&

.MARINE...LOW LEVEL ONSHORE FLOW PATTERN WILL CONTINUE THROUGH THE
WEEKEND. HIGHEST WINDS AND WAVES ARE EXPECTED IN THE CENTRAL AND
EAST STRAIT OF JUAN DE FUCA DURING THE LATE AFTERNOON AND EVENING
HOURS. KUIL-KBLI PRES GRADIENT IS UP TO 3.3 MB THIS EVENING - A GALE
WARNING IS IN EFFECT FOR THE CENTRAL AND EAST STRAIT. A WEAK COLD
FRONT WILL CROSS WESTERN WA THURSDAY MORNING...FOLLOWED BY ANOTHER
WEAK SYSTEM ON FRIDAY. BOTH OF THESE SYSTEMS ARE NOT STRONG ENOUGH
TO DISRUPT THE ONSHORE FLOW PATTERN.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...GALE WARNING CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA.
     SMALL CRAFT ADVISORY ADMIRALTY INLET...AND NORTHERN INLAND
     WATERS.

&&

$$

WWW.WEATHER.GOV/SEATTLE

YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT
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