Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 220410
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
915 PM PDT THU MAY 21 2015

.SYNOPSIS...SHOWERS AND THUNDERSTORMS OVER THE CASCADES WILL
DIMINISH OVERNIGHT. MARINE STRATUS ALONG THE COAST WILL PUSH INLAND
OVERNIGHT. FRIDAY AND SATURDAY WILL BE COOLER WITH A CHANCE OF
SHOWERS OVER THE INTERIOR OF WESTERN WASHINGTON AND THE CASCADES. A
PATTERN OF MORNING CLOUDS WITH SOME AFTERNOON SUNSHINE IS LIKELY
NEXT WEEK WITH A CONTINUING CHANCE OF SHOWERS IN THE MOUNTAINS.

&&

.SHORT TERM...A COMPLICATED WEST COAST BLOCKING PATTERN CONTINUES
THIS EVENING WITH A 573 DAM 500 MB HIGH OVER THE YUKON  SOUTHEAST
INTO A RIDGE IN THE NORTHERN PLAINS...AND AN UPPER LOW OVER SOUTHERN
CALIFORNIA WITH DISTURBANCES OVER EXTREME SE ALASKA AND OVER
WASHINGTON STATE. WHILE THE LARGE SCALE FEATURES APPEAR TO BE
HANDLED WELL AND WITH RATHER GOOD CONSISTENCY THROUGH THE MIDDLE OF
NEXT WEEK...THERE CONTINUE TO BE SOME MINOR PLACEMENT ISSUES WITH
SMALL SHORT WAVE FEATURES WITHIN THE MEAN RIDGE TO THE NORTH AND THE
TROUGH TO THE SOUTH.

THUNDERSTORMS OVER THE CASCADES ARE RAPIDLY DIMINISHING THIS EVENING
AS THE SUN GOES DOWN. EARLIER THERE WERE SOME STRONG THUNDERSTORMS
AND ONE SEVERE THUNDERSTORM OVER THE NORTH CASCADES...ALL DUE TO
RADAR INDICATED HAIL. EXPECT CONVECTION TO POP BACK UP OVER THE
MOUNTAINS FRIDAY AFTERNOON AND EVENING. SHOWER CHANCES IN THE
LOWLANDS WILL BE LOW WITH UPPER FLOW MAINLY FROM THE SSE AHEAD OF
THE CUTOFF FEATURE DROPPING SSE FROM THE ALASKAN PANHANDLE...BUT
THEY CANNOT BE RULED OUT DURING THE LATE AFTERNOON AND EVENING.
KOTH-KSEA PRESSURE GRADIENT AT 03Z IS OVER 4.5 MB AND THERE IS GOOD
INFLOW THROUGH THE STRAIT. SO EXPECT THE EXTENSIVE MARINE STRATUS
THAT IS SEEN ALONG THE COAST AND OVER THE COASTAL WATERS TO STREAM
INLAND OVERNIGHT AND POSSIBLY TO NOT BURN OFF FRIDAY AFTERNOON. THE
CURRENT HIGH TEMPERATURE FORECAST FOR MID 60S IN THE INTERIOR MAY BE
A BIT OPTIMISTIC...BUT WITH ANY BREAK AT ALL WOULD NOT BE DIFFICULT
TO REACH.

THE FIRST UPPER LOW COMING DOWN FROM THE NORTHWEST MOVES WELL SOUTH
OF THE AREA ON SATURDAY AND IS FOLLOWED BY ANOTHER LATE IN THE
WEEKEND INTO EARLY NEXT WEEK. IN THE MEANTIME...THE ONSHORE FLOW
WILL CONTINUE TO BRING LOW LEVEL MOISTURE INLAND. THIS WILL KEEP
HIGHS IN THE 60S...LOWS IN THE UPPER 40S TO MID 50S...AND A CHANCE
OF SHOWERS GOING...MAINLY OVER THE CASCADES.

THE FORECAST FOR TONIGHT INTO FRIDAY MORNING WAS UPDATED TO REMOVE
SHOWERS FROM THE LOWLANDS AND OLYMPICS...WHERE THINGS HAVE SETTLED
DOWN. THE REMAINDER OF THE FORECAST LOOKS GOOD. ALBRECHT

.LONG TERM...FROM THE PREVIOUS LONG TERM DISCUSSION...ANOTHER WEAK
UPPER LOW WILL REMAIN OVER THE REGION SUNDAY THROUGH WEDNESDAY WITH
CONTINUED MODERATE LOW LEVEL ONSHORE FLOW. MOST DAYS SHOULD SEE
MORNING CLOUDS WITH SOME AFTERNOON SUNSHINE OVER THE INTERIOR. THE
COAST WILL PROBABLY STAY CLOUDY AND COOL EACH DAY. THERE WILL BE A
CHANCE OF SHOWERS...MAINLY IN THE MOUNTAINS EACH AFTERNOON AND
EVENING HOURS. THE POSITION OF THE LOW CHANGES FROM RUN TO RUN AND
SO IT IS HARD TO SAY IF THE LOWLANDS WILL SEE ANY SHOWERS...BUT THE
NORTH CASCADES PROBABLY HAVE THE BEST CHANCE OF SHOWERS AND COULD
SEE A SOAKING RAIN OR TWO IF THE LOW BRINGS MOISTURE WWD FROM
EASTERN WA...WHICH SOME MODELS RUNS HAVE SHOWN.

&&

.AVIATION...AN UPPER LOW OVER THE CENTRAL COAST OF BRITISH COLUMBIA
WILL REMAIN STATIONARY THROUGH FRIDAY KEEPING THE FLOW ALOFT LIGHT.
AIR MASS STABILIZING QUICKLY OVER THE HIGHER TERRAIN TONIGHT. LOW
LEVEL ONSHORE FLOW CONTINUING THROUGH FRIDAY.

SATELLITE IMAGERY SHOWS CONVECTION DYING OFF RAPIDLY THIS EVENING.
STRATUS ALONG THE COAST ALREADY MOVING INTO THE CHEHALIS RIVER
VALLEY BUT NOT DOWN THE STRAIT YET. WITH THE ONSHORE GRADIENTS
INCREASING OVERNIGHT EXPECT THE STRATUS TO GET TO ALL OF THE
INTERIOR TERMINALS BY 13Z FRIDAY MORNING WITH CEILINGS BELOW 1000
FEET. CEILINGS LIFTING UP INTO THE 1000-2000 FOOT RANGE LATER IN THE
MORNING AND UP TO NEAR 3000 FEET IN THE AFTERNOON. WITH THE ONSHORE
FLOW CONTINUING ALL DAY NOT EXPECTING CLOUDS TO SCATTER OUT LATE IN
THE AFTERNOON EXCEPT OVER THE NORTHWEST INTERIOR.

KSEA...JUST SOME MID AND HIGH LEVEL CLOUDS THIS EVENING. STRATUS
ARRIVING AROUND 09Z WITH CEILINGS LOWERING TO LESS THAN 1000 FEET.
CEILINGS LIFTING MID TO LATE MORNING TO 1000-1500 FEET AND UP TO
NEAR 3000 FEET IN THE AFTERNOON. LIGHT WIND BECOMING SOUTHERLY 4 TO
8 KNOTS EARLY FRIDAY MORNING.

&&

.MARINE...PERSISTENT HIGH PRES OFFSHORE WITH LOWER PRES INLAND WILL
RESULT IN CONTINUED ONSHORE FLOW OF VARYING STRENGTH THROUGH TUE.

GALE FORCE WINDS IN THE CENTRAL AND EASTERN STRAIT WILL EASE LATE
TONIGHT. WITH THE ONSHORE GRADIENTS CONTINUING FRIDAY THERE IS THE
POSSIBILITY OF ANOTHER ROUND OF GALE FOR THE CENTRAL AND EASTERN
STRAIT FRIDAY EVENING. EXPECT SMALL CRAFT ADVISORY WINDS LATE IN THE
DAY SATURDAY THROUGH THE FIRST PART OF NEXT WEEK FOR THE CENTRAL AND
EASTERN STRAIT WITH WINDS BELOW 20 KNOTS OVER THE REMAINDER OF THE
WATERS. FELTON


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...GALE WARNING IN EFFECT TIL 5 AM FRI FOR THE CENTRAL STRAIT OF
      JUAN DE FUCA AND THE EAST ENTRANCE.

     SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE COASTAL WATERS
      FROM CAPE FLATTERY TO CAPE SHOALWATER FROM 10 NM OUT TO
      60 NM.

&&

$$











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