Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 160322
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
820 PM PDT MON SEP 15 2014

.SYNOPSIS...DEVELOPING LOW LEVEL ONSHORE WILL BRING MARINE CLOUDS TO
THE COAST AND PARTS OF THE INTERIOR THROUGH TUESDAY ALONG WITH MUCH
COOLER DAYTIME TEMPERATURES. A THREAT OF SHOWERS IS EXPECTED
WEDNESDAY INTO FRIDAY AS AN APPROACHING LOW PRESSURE SYSTEM ALOFT
MOVES ONSHORE WITH THE BEST SHOWER CHANCE ON THURSDAY. REBUILDING
HIGHER PRESSURE ALOFT THIS WEEKEND SHOULD PRODUCE MORE WARM SUNNY
AND DRY WEATHER.

&&

.SHORT TERM...THE UPPER RIDGE WAS OVER THE PACIFIC NW INTERIOR THIS
EVENING WITH SOUTHERLY FLOW ALOFT OVER WA. AN UPPER TROUGH WAS IN
THE VICINITY OF 140W WITH A COUPLE OF SHORTWAVES ROTATING THROUGH
IT. THE FIRST WAS MOVING NORTH THROUGH WESTERN OREGON. GOOD
DIFFLUENT FLOW ALOFT BUT LIMITED MOISTURE. AT THIS HOUR...IT WAS
NOTHING BUT SOME HIGHER LEVEL CLOUDS THOUGH KEEPING AN EYE ON ANY
SHORT-FUSED DEVELOPING HIGH LEVEL CONVECTION.

THIS SHORTWAVE HAS HAD SURFACE REFLECTION THOUGH. LOW LEVEL ONSHORE
FLOW HAS BEGUN AND STRATUS/FOG MOVING UP THE OREGON COAST TODAY WAS
CONTINUING UP THE WA COAST THIS EVENING. EXPECT IT TO PENETRATE INTO
AT LEAST THE SOUTH SOUND THROUGH THE CHEHALIS GAP - PERHAPS AS FAR
AS SEATAC AIRPORT - AND PARTS OF THE STRAIT TUE MORNING. USING THE
OLD PHRASE - STRATUS COMING AT US. THE COOLER MARINE AIR MASS WILL
ALSO KNOCK HIGH TEMPS TUE DOWN ABOUT 10 TO 20 DEGREES IN MANY
PLACES...VERY NOTICEABLE AND FOR SOME - QUITE REFRESHING.

THE 00Z PROGS IN THUS FAR CONTINUE THE TREND OF TRACKING THE NEXT
SHORTWAVE AND UPPER TROUGH ONSHORE WED AND THU FOR THE FIRST REAL
THREAT OF SHOWERS IN ABOUT TWO WEEKS. EVEN COOLER MAX TEMPS TOO.
FORECAST HERE IS ON TRACK.

TRIVIA NEWS BIT - AS OF TODAY...KSEA HAS HIT 80 DEGREES OR BETTER
45 TIMES THIS YEAR...NOW TIED FOR THIRD MOST NUMBER OF DAYS WITH
1961. THE RECORD IS 47 DAYS IN 1958. NUMBER 2 IS 46 DAYS IN 1967.
COULD 80 BE HIT AGAIN THIS WEEKEND? STAY TUNED. BUEHNER

.LONG TERM...FROM PREVIOUS DISCUSSION...ON FRIDAY THERE WILL BE SOME
RESIDUAL SHOWERS...MOSTLY IN THE MOUNTAINS. AN UPPER RIDGE BUILDS
OVER THE WEEKEND WITH THE GFS SHOWING HEIGHTS IN THE MID 580S BUT
THE EURO PUSHING NEARLY TO 590DM. SKIES WILL BE SUNNY AND
TEMPERATURES SHOULD REACH AT LEAST THE LOW 80S IN MANY PLACES BY
SUNDAY. THE GFS HAS A WEAK SYSTEM APPROACHING BY MONDAY SO LOWER
TEMPERATURES ARE LIKELY AND THERE WILL BE A CHANCE OF SHOWERS. BURKE

&&

.AVIATION...AREAS OF FOG AND MARINE STRATUS ARE SPREADING NORTH
ALONG THE WA COAST THIS EVENING AS ONSHORE FLOW DEVELOPS. FOG AND
LOW CLOUDS WILL SPREAD INTO THE CHEHALIS GAP AND SHOULD MAKE IT INTO
PUGET SOUND AROUND DAYBREAK. OTHERWISE...THE RIDGE IS MOVING EAST
AND SW FLOW ALOFT WILL INCREASE THROUGH TUESDAY...GIVING SOME MID
AND HIGH CLOUDS. THE AIR MASS WILL BECOME UNSTABLE IN THE MID LEVELS
THROUGH TUESDAY AND AT THE LEAST SOME CONVECTIVE DEBRIS FROM OREGON
WILL SPREAD INTO WRN WA. THE BEST CHANCE OF A THUNDERSTORM WILL BE
IN THE CASCADES.

KSEA...LIGHT WINDS AND INCREASING CIRRUS...THEN DEVELOPING ONSHORE
FLOW WILL GIVE A SLY BREEZE TUESDAY. SEVERAL HOURS OF MORNING LOW
CLOUDS AND FOG AREA A GOOD BET TUESDAY. TAF LOOKS PRETTY GOOD NO BIG
CHANGES EXPECTED THIS EVENING.

&&

.MARINE...FOG AND LOW CLOUDS ARE MOVING NORTH ALONG THE COAST AS
ONSHORE FLOW DEVELOPS THIS EVENING. PRESSURE GRADIENTS WILL
INCREASE THROUGH THE STRAIGHT OF JUAN DE FUCA THROUGH THE DAY
TUESDAY WITH WITH SMALL CRAFT ADVISORY STRENGTH WESTERLIES LIKELY IN
THE AFTERNOON AND EVENING. GRADIENTS WILL BE ON THE LIGHT SIDE WED
THRU FRI.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&

$$

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