Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 211118
AFDSEW

AREA FORECAST DISCUSSION...CORRECTED SYNOPSIS
NATIONAL WEATHER SERVICE SEATTLE WA
415 AM PDT SUN SEP 21 2014

.SYNOPSIS...UPPER LEVEL RIDGE OVER THE AREA SHIFTING EAST TODAY AND
TONIGHT. A WEAKENING FRONT WILL DISSIPATE NEAR THE COAST MONDAY. A
STRONGER FRONT WILL ARRIVE ON WEDNESDAY WITH RAIN OUT AHEAD OF THE
SYSTEM TUESDAY NIGHT. A LARGE TROUGH OF LOW PRESSURE OFFSHORE WILL
KEEP THE WEATHER UNSETTLED INTO NEXT WEEKEND.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS CLEAR SKIES ACROSS THE AREA
THIS MORNING. STRATUS MOVING NORTH THROUGH THE COASTAL WATERS STILL
OFFSHORE AT 10Z. TEMPERATURES AT 10Z/3 AM WERE IN THE 50S AND LOWER
60S.

LITTLE CHANGE IN THE SHORT TERM FORECAST WITH TODAY BEING THE LAST
WARM DAY FOR THE INTERIOR MORE THAN LIKELY FOR THE SEASON. UPPER
LEVEL RIDGE OVER THE AREA SHIFTING EAST TODAY. TEMPERATURE ALOFT
STILL WARM EVEN WITH THE RIDGE SHIFTING EAST...850 MB TEMPERATURES
STILL PLUS 15C TO PLUS 19C AT 00Z MONDAY. OFFSHORE SURFACE GRADIENTS
THIS MORNING WILL TURN ONSHORE LATER THIS MORNING INTO THIS
AFTERNOON. THIS WILL PULL THE STRATUS OVER THE COASTAL WATERS INLAND
ALONG THE COAST KEEPING HIGHS IN THE 60S TO LOWER 70S. FOR THE
INTERIOR EVEN WITH THE TEMPERATURES ALOFT A LITTLE COOLER THAN
YESTERDAY THE LACK OF MORNING CLOUDS WILL ALLOW TEMPERATURES TO WARM
UP QUICKER THAN SATURDAY WITH HIGHS EXPECTED TO BE UP TO 10 DEGREES
WARMER THAN YESTERDAY...MID 70S TO MID 80S.

LOW LEVEL ONSHORE FLOW CONTINUING TONIGHT WITH A MARINE PUSH
OVERNIGHT INTO MONDAY MORNING PULLING THE STRATUS ALONG THE COAST
INLAND AFTER MIDNIGHT. WITH THE INCREASING CLOUD COVER LOW
TEMPERATURES WILL BE IN A NARROW RANGE...IN THE 50S.

LOW LEVEL ONSHORE FLOW CONTINUING MONDAY WITH A WEAK SURFACE RIDGE
ALONG THE COAST OUT AHEAD OF A WEAKENING FRONT OFFSHORE. THE
COMBINATION OF THE STRATUS IN THE MORNING AND INCREASING MOD AND
HIGH LEVEL CLOUDS IN THE AFTERNOON WILL KEEP SKIES AT LEAST MOSTLY
CLOUDY ON MONDAY. HIGHS WILL BE MUCH COOLER OVER THE INTERIOR WITH
MID 60S TO LOWER 70S.

FRONT DISSIPATING NEAR THE COAST MONDAY NIGHT WITH A CHANCE OF
SHOWERS ALONG THE COAST AND OVER THE NORTHERN SECTIONS OF THE AREA.

THE FIRST ORGANIZED SYSTEM OF FALL APPROACHING THE AREA TUESDAY
MORNING. 00Z MODELS HAVE SPED UP THE TIMING OF THE WARM FRONT.
BECAUSE OF THIS HAVE INCREASED THE POPS OVER THE INTERIOR INTO THE
CHANCE CATEGORY FOR TUESDAY AFTERNOON AND GONE WITH LIKELY POPS
ALONG THE COAST.

.LONG TERM...EXTENDED MODELS IN GOOD AGREEMENT TUESDAY NIGHT INTO
WEDNESDAY WITH THE COLD FRONT ASSOCIATED WITH A VERTICALLY STACKED
LOW NEAR 135W MOVING INTO THE AREA. THIS SYSTEM WILL BE THE WETTEST
SYSTEM IN OVER A MONTH WITH THE POTENTIAL FOR OVER AN INCH OF RAIN
ALONG THE COAST...OLYMPICS AND LOWER CHEHALIS VALLEY AND OVER A HALF
AN INCH FOR THE REMAINDER OF THE INTERIOR. CURRENT MODEL TIMING HAS
THE FRONT MOVING THROUGH DURING THE DAY ON WEDNESDAY SO HAVE GONE
WITH HIGHER POPS IN THE MORNING. VERTICALLY STACKED LOW REMAINING
OFF VANCOUVER ISLAND WEDNESDAY NIGHT INTO THURSDAY WITH A DEEP
TROUGH ALONG THE WEST COAST. THIS WILL KEEP AT LEAST A CHANCE OF
SHOWERS IN THE FORECAST. UPPER LEVEL LOW DISSIPATING ON FRIDAY WITH
THE UPPER LEVEL TROUGH MOVING INLAND KEEPING A CHANCE OF SHOWERS IN
THE FORECAST. BOTH THE ECMWF AND GFS INDICATING A LITTLE BIT OF
RIDGE ON SATURDAY WITH THE ECMWF A LITTLE STRONGER WITH THE RIDGING.
GFS STILL HAS SOME LIGHT PRECIPITATION HOLDING ON IN THE TRANSITION
TO A RIDGE SATURDAY MORNING SO FOR NOW WILL KEEP THE CHANCE OF
SHOWERS IN THE FORECAST FOR SATURDAY AS WELL. FELTON

&&

.AVIATION...SOUTHWEST FLOW ALOFT WITH AN UPPER LEVEL TROUGH OVER THE
NORTHEAST PACIFIC. AT THE SURFACE...ONSHORE FLOW WILL DEVELOP TODAY
WITH A RIDGE MOVING OVER THE COAST. A WEAKENING FRONT WILL MOVE INTO
THE COASTAL WATERS TONIGHT. AIR MASS GENERALLY DRY AND STABLE.

STRATUS WILL PUSH NORTH ALONG THE IMMEDIATE COAST EARLY THIS
MORNING. IT IS EXPECTED TO REMAIN NEAR THE COAST TODAY...THEN PUSH
INLAND TONIGHT. THERE WILL ALSO BE PATCHY VALLEY FOG THIS MORNING.

KSEA...CLEAR SKIES. LIGHT WIND BECOMING SOUTHERLY 4-8 KNOTS TODAY.
COASTAL STRATUS SHOULD REACH THE TERMINAL LATE TONIGHT...PROBABLY
ACCOMPANIED BY SOME FOG. SCHNEIDER

&&

.MARINE...ONSHORE FLOW WILL DEVELOP TODAY AS A SURFACE RIDGE MOVES
TO THE COAST. A WEAK FRONT WILL MOVE THROUGH THE WATERS ON MONDAY. A
STRONGER FRONTAL SYSTEM WILL ARRIVE TUESDAY AND WEDNESDAY. THIS
SYSTEM COULD BRING GALE SOUTHERLY WINDS TO THE COASTAL WATERS.
SCHNEIDER

&&

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

&&

$$

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