Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 202220
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
320 PM PDT WED AUG 20 2014

.SYNOPSIS...LOW LEVEL ONSHORE FLOW IS EXPECTED TO CONTINUE INTO
FRIDAY MAINTAINING AREAS OF MARINE CLOUDS AND COOLER THAN AVERAGE
TEMPERATURES. A WEAK LOW PRESSURE SYSTEM ALOFT IS EXPECTED TO MOVE
ONSHORE FROM THE GULF OF ALASKA LATER THURSDAY AND FRIDAY BRINGING A
THREAT OF SHOWERS MAINLY TO THE MOUNTAINS. HIGHER PRESSURE ALOFT IS
FORECAST TO BUILD ONSHORE OVER THE WEEKEND AND INTO NEXT WEEK FOR
WARMER WEATHER AND MORE SUNSHINE.

&&

.SHORT TERM...THE LONG WAVE RIDGE WAS OVER THE NE PACIFIC THIS
AFTERNOON WHILE A LONG WAVE TROUGH WAS NEAR THE DATELINE. WATER
VAPOR SATELLITE IMAGES SHOWED A WEAK SHORTWAVE MOVING ACROSS THE TOP
OF THE GULF OF ALASKA RIDGE THAT THE PROGS ALL AGREE WILL DIG SE
INTO THE PACIFIC NW THU AND FRI. THIS SYSTEM WILL MAINTAIN LOW LEVEL
ONSHORE FLOW INTO WESTERN WA AND BRING A THREAT OF SHOWERS PRIMARILY
TO THE MOUNTAINS. ENOUGH INSTABILITY TO INCLUDE A THREAT OF TSTMS IN
THE CASCADES AS WELL ON FRIDAY.

WITH THE ONSHORE FLOW...AREAS OF MARINE CLOUDS SHOULD RETURN EACH
NIGHT AND MORNING WITH SOME AFTERNOON CLEARING. IN ADDITION DAYTIME
TEMPERATURES WILL LIKELY REMAIN A BIT BELOW SEASONAL AVERAGES.

THAT SYSTEM DIGS FURTHER SE FRIDAY NIGHT AND SATURDAY WITH ONLY A
LINGERING THREAT OF SHOWERS NEAR THE CASCADE CREST. THE RIDGE
OFFSHORE REBUILDS WITH NW FLOW ALOFT INTO WA. LOW LEVEL ONSHORE FLOW
WEAKENS. ALL THIS PERMITS MORE SUNSHINE AND WARMER DAYTIME
TEMPERATURES ON SATURDAY. BUEHNER

.LONG TERM...ALL THE PROGS SEEM TO BE GENERALLY ON THE SAME PAGE
THROUGH WEDNESDAY. THE RIDGING ALOFT AND WARMING TREND CONTINUES
INTO SUNDAY. SO THE WEEKEND LOOKS TO HAVE MORE SUNSHINE AND HIGH
TEMPS RISING TO AROUND OR A BIT ABOVE AVERAGE. A WEAK SHORTWAVE DIGS
SE MONDAY IN THAT NW FLOW ALOFT SUNDAY NIGHT AND MONDAY. THE PRIMARY
IMPACT ON WESTERN WA WILL BE TO INCREASE LOW LEVEL ONSHORE FLOW FOR
A BRIEF COOL DOWN. THEN THE RIDGE ALOFT REBOUNDS TUESDAY AND
WEDNESDAY WITH LOW LEVEL ONSHORE FLOW AGAIN EASING FOR MORE SUNSHINE
AND TEMPS RISING A BIT ABOVE SEASONAL NORMS. BUEHNER

&&

.AVIATION...FLOW ALOFT WILL REMAIN NORTHWEST TONIGHT...THEN BECOME
WEST EARLY THURSDAY MORNING AS A WEAK UPPER LEVEL SHORTWAVE TROUGH
APPROACHES FROM NORTHWEST. LOW LEVEL FLOW WILL REMAIN ONSHORE WITH
PERSISTENT HIGH PRESSURE OVER THE OFFSHORE WATERS AND LOWER PRESSURE
INLAND. THE AIR MASS WILL REMAIN STABLE TONIGHT WITH LINGERING LOW
LEVEL MOISTURE. THE APPROACHING...ALBEIT WEAK...UPPER LEVEL
SHORTWAVE TROUGH MAY JUST PRODUCE ENOUGH LIFT TO PRODUCE DRIZZLE
AND/OR LIGHT RAIN FROM THE STRATUS LAYER TOMORROW ESPECIALLY OVER
THE COAST.

SKIES HAVE ALL BUT SCATTERED OUT THIS AFTERNOON...WITH THE EXCEPTION
OF THE SOUTH SOUND WHERE A BKN 3K FT DECK CONTINUES TO LINGER.
EXPECT THE CLOUDS TO CONTINUE TO LIFT AND DISSIPATE OVER THE NEXT
FEW HOURS...REMAINING VFR THROUGH 06Z FOR THE COAST AND 10Z OVER THE
INTERIOR. EXPECT CEILINGS TO LOWER TO MVFR AND IFR LEVELS AGAIN
THURSDAY MORNING...LIFTING LATE IN THE MORNING TO VFR CONDITIONS AND
SCATTERING OUT LATE IN THE AFTERNOON.

KSEA...VFR CONDITIONS WILL PERSIST THROUGH THE EVENING WITH CEILINGS
LOWERING TO MVFR LEVELS AROUND 11Z...AND IMPROVING BY 18Z. SOUTHWEST
WINDS 6 TO 8 KT WILL EAST TO 4 TO 6 KT AND BECOME SOUTH LATE
TONIGHT.

&&

.MARINE...THE VERY STATIC ONSHORE FLOW PATTERN WILL CONTINUE FOR THE
NEXT SEVERAL DAYS. HIGH PRESSURE OVER THE OFFSHORE WATERS AND LOWER
PRESSURE INLAND WILL DRIVE WESTERLY WINDS NEAR SMALL CRAFT ADVISORY
LEVELS THROUGH THE CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA MOST
EVENINGS.


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY CENTRAL AND EAST STRAIT OF JUAN DE
FUCA.

&&

$$

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