Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 241016
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
315 AM PDT SUN MAY 24 2015

.SYNOPSIS...A SURFACE RIDGE OFFSHORE WILL MAINTAIN LOW LEVEL ONSHORE
FLOW OVER WESTERN WASHINGTON THROUGH MID WEEK. THIS WILL KEEP SKIES
MOSTLY CLOUDY. WEAKER ONSHORE FLOW AFTER MID WEEK WILL ALLOW MORE
AFTERNOON SUNSHINE AND A WARMING TREND. THE AIR MASS OVER THE
CASCADES WILL CONTINUE TO BECOME SLIGHTLY UNSTABLE LATE IN THE DAY
KEEPING A CHANCE OF SHOWERS IN THE FORECAST FOR THAT AREA.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS CLOUDY SKIES OVER WESTERN
WASHINGTON EARLY THIS MORNING. NO PRECIPITATION ECHOES HAVE POPPED
UP ON THE RADARS SINCE EARLY YESTERDAY EVENING. TEMPERATURES WERE IN
A NARROW RANGE AT 3 AM...LOWER TO MID 50S.

LITTLE CHANGE IN THE FORECAST TODAY WITH LOW LEVEL ONSHORE FLOW
KEEPING SKIES CLOUDY AND WEAK LOW PRESSURE ALOFT KEEPING THE THREAT
OF SHOWERS DEVELOPING LATE IN THE DAY OVER THE CASCADES. WITH PLENTY
OF CLOUD COVER THE TEMPERATURE SPREAD BETWEEN HIGH AND LOW
TEMPERATURES WILL BE 10 DEGREES OR LESS PUTTING HIGHS IN THE MID 50S
TO LOWER 60S TODAY. SOME SMALL CHANGES IN THE UPPER LEVEL PATTERN
LATER TODAY AS A WEAK UPPER LEVEL LOW MOVES DOWN THE BRITISH
COLUMBIA COAST INTO SOUTHERN BRITISH COLUMBIA BY 00Z MONDAY. THIS
WILL TURN THE FLOW ALOFT OVER WESTERN WASHINGTON WEST NORTHWESTERLY
WHICH WILL PUSH ANY CONVECTION THAT DEVELOPS OVER THE CASCADES LATER
TODAY TO THE EAST SLOPES.

UPPER LEVEL LOW CONTINUING TO DRIFT SOUTHEAST TONIGHT AND MEMORIAL
DAY ENDING UP OVER EASTERN WASHINGTON BY MEMORIAL DAY AFTERNOON. THE
SLIGHTLY UNSTABLE AIR MASS PLUS MOISTURE ROTATING AROUND THE LOW
WILL KEEP THE THREAT OF SHOWERS IN THE FORECAST FOR THE CASCADES.
FLOW ALOFT WILL BECOME NORTHERLY OVER THE AREA WHICH WILL KEEP THE
SHOWER ACTIVITY CONFINED TO THE MOUNTAINS. IN THE LOWER LEVELS
ONSHORE FLOW CONTINUING KEEPING SKIES CLOUDY. THE ONSHORE FLOW
WEAKENS SLIGHTLY LATER IN THE DAY ON MEMORIAL DAY. THIS SHOULD THIN
OUT THE MARINE LAYER A TOUCH SO THERE COULD BE SOME AFTERNOON
SUNBREAKS. HIGH TEMPERATURES WILL CREEP UP TO NEAR NORMAL ON
MEMORIAL DAY...UPPER 50S TO MID 60S.

UPPER LEVEL LOW WOBBLING AROUND OVER EASTERN WASHINGTON MONDAY NIGHT
AND TUESDAY WITH THE LOW MOVING SOUTHEAST TO NEAR THE WALLOWA
MOUNTAINS BY 00Z WEDNESDAY. LOW STILL NOT FAR ENOUGH AWAY TO KEEP
THE THREAT OF LATE DAY CONVECTION OUT OF THE CASCADES WITH THE BEST
CHANCES NEAR THE CREST. FOR THE LOWLANDS ONSHORE FLOW CONTINUING
KEEPING SKIES CLOUDY. ONCE AGAIN THE MARINE LAYER THINS OUT A BIT
TUESDAY AFTERNOON FOR THE POSSIBILITY OF A LITTLE SUNSHINE. HIGH IN
THE UPPER 50S TO MID 60S WILL BE COMMON.

.LONG TERM...EXTENDED MODELS AGAIN IN GOOD AGREEMENT WITH THE UPPER
LEVEL LOW MOVING SOUTHEAST ON WEDNESDAY AND AN UPPER LEVEL RIDGE
BUILDING OFF THE COAST. UPPER LEVEL RIDGE MOVING OVER THE AREA LATER
THURSDAY INTO FRIDAY AND REMAINING OVER THE AREA ON SATURDAY. 500 MB
HEIGHTS RISE INTO THE MID TO UPPER 570 DMS WITH 850 MB TEMPERATURES
WARMING TO AROUND PLUS 15C. SURFACE GRADIENTS REMAIN ONSHORE WHICH
WILL TEMPER THE WARMING TREND SOMEWHAT BUT THE ONSHORE GRADIENTS
ALSO WEAKEN LEADING TO MORE SUNSHINE AND WARMER DAYS. HIGHS WILL GET
INTO THE 70S IN MANY LOCATIONS IN THE INTERIOR ON THURSDAY AND
REMAIN IN THE 70S THROUGH SATURDAY. THE AIR MASS OVER THE CASCADES
WILL REMAIN SLIGHTLY UNSTABLE KEEPING THE THREAT OF LATE DAY
CONVECTION IN THE FORECAST. FELTON

&&

.AVIATION...A WEAK UPPER LEVEL LOW IN SOUTHERN BRITISH COLUMBIA WILL
MOVE SLOWLY SOUTHEAST TODAY. THIS SYSTEM WILL INCREASE ONSHORE FLOW
AND DEEPEN THE MARINE LAYER. AT THE SURFACE ONSHORE FLOW WILL
INCREASE THIS AFTERNOON. THE AIR MASS IS MOIST AND WEAKLY UNSTABLE.

LOW LEVEL MOISTURE AND A DEEP MARINE LAYER WILL RESULT IN WIDESPREAD
MVFR CEILINGS THROUGH THIS MORNING. CEILINGS WILL LIFT TO VFR AFTER
MIDDAY BUT BREAKOUT IS UNLIKELY AT MOST TERMINALS.

KSEA...CEILING 1-2K FT THIS MORNING GRADUALLY LIFTING TO 3-4K
FT IN THE AFTERNOON BUT BREAKOUT IS NOT EXPECTED. SW WIND 4-8 KT. CHB

&&

.MARINE...HIGH PRES WILL REMAIN OFFSHORE WITH LOWER PRES INLAND.
SMALL CRAFT ADVISORY STRENGTH WESTERLY WINDS WILL CONTINUE FOR A FEW
HOURS THIS MORNING IN THE STRAIT BEFORE TEMPORARILY DIMINISHING.
SMALL CRAFT ADVISORY STRENGTH WESTERLY WINDS ARE LIKELY EACH EVENING
IN THE STRAIT TONIGHT THROUGH TUESDAY NIGHT. THERE IS A POSSIBILITY
OF BRIEF GALE STRENGTH WIND TONIGHT. ONSHORE FLOW WILL WEAKEN
WEDNESDAY AND THURSDAY. CHB

&&

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

&&

$$

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