Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 051101
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
400 AM PDT TUE MAY 5 2015

.SYNOPSIS...AN UPPER LEVEL LOW WILL MOVE OVER WESTERN WASHINGTON
TODAY BRINGING SHOWERS WITH A CHANCE OF THUNDERSTORMS TO THE AREA.
THE LOW WILL MOVE OFF TO THE SOUTH AND EAST ON WEDNESDAY DECREASING
THE CHANCE OF SHOWERS. AN UPPER LEVEL RIDGE WILL BUILD OFF THE COAST
AND MOVE OVER WESTERN WASHINGTON BY THE WEEKEND WITH SUNNIER AND
WARMER WEATHER BEGINNING THURSDAY.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS UPPER LEVEL LOW CENTERED OVER
CENTRAL VANCOUVER ISLAND AT 10Z/3AM. ORGANIZED BAND OF SHOWERS
ROTATING AROUND THE LOW JUST REACHING THE COAST. MOSTLY CLOUDY SKIES
ACROSS THE AREA AT 10Z/3 AM WITH TEMPERATURES IN THE 40S AND LOWER
50S.

LITTLE CHANGE IN THE FORECAST THIS MORNING WITH THE MODEL SOLUTIONS
REMAINING CONSISTENT MOVING THE LOW A LITTLE SOUTH AND EAST TODAY
OVER SOUTHERN BRITISH COLUMBIA AND NORTHERN WASHINGTON BY 00Z WED.
BANDS OF SHOWERS ROTATING AROUND THE LOW WILL MOVE THROUGH WESTERN
WASHINGTON THROUGHOUT THE DAY. CURRENT LIGHTNING DATA NOT INDICATING
ANY STRIKES SO FAR OVERNIGHT. CLOUD TOPS ON THE SATELLITE IMAGERY
NOT SHOWING MUCH COOLING WITH THE CURRENT BAND MOVING INTO WESTERN
WASHINGTON. WITH THE LOW APPROACHING THE AREA COLDER AIR MASS NOT
REACHING WESTERN WASHINGTON UNTIL THIS AFTERNOON. CONVECTIVE
TEMPERATURES OFF THE MODEL SOUNDING CONTINUE TO BE IN THE MID AND
UPPER 50S. LOWEST LIFTED INDEXES...AS LOW AS -3...OCCURING THIS
AFTERNOON. GIVEN ALL THESE VARIABLES HAVE CONFINED THE CHANCE OF
THUNDERSTORMS TO THE AFTERNOON AND EVENING HOURS. TEMPERATURES WILL
BE ON THE COOL SIDE TODAY WITH HIGHS ONLY IN THE 50S.

LOW STILL HANGING OVER THE AREA TONIGHT KEEPING SHOWERS IN THE
FORECAST ALONG WITH A CHANCE OF EVENING THUNDERSTORMS. THE LOW WILL
SLOWLY MOVE EAST OVERNIGHT AND BY 12Z WED WILL BE CENTERED OVER
EASTERN WASHINGTON. LOWS TONIGHT WILL BE MOSTLY IN THE UPPER 30S AND
40S.

LOW MOVING SOUTH ON WEDNESDAY WITH THE LOW CENTERED OVER EASTERN
OREGON BY 00Z THURSDAY. FLOW ALOFT BECOMING NORTHERLY OVER WESTERN
WASHINGTON. AIR MASS STILL SOMEWHAT UNSTABLE WEDNESDAY AFTERNOON
WITH LIFTED INDEXES STILL NEAR 0 SO WILL HAVE TO KEEP A CHANCE OF
SHOWERS IN THE FORECAST. TEMPERATURES ALOFT FAIRLY SIMILAR TO
TUESDAY BUT WITH A LITTLE MORE SUNSHINE A FEW HIGH TEMPERATURES WILL
CREEP INTO THE LOWER 60S. MID AND UPPER 50S FOR THE REMAINDER OF THE
AREA.

DRYING AND WARMING TREND BEGINNING WEDNESDAY NIGHT AND CONTINUING
INTO THURSDAY AS THE LOW RAPIDLY MOVES SOUTH AND AN UPPER LEVEL
RIDGE BUILDS OFF THE COAST. WITH PLENTY OF SUNSHINE AND WARMING
TEMPERATURES ALOFT HIGHS WILL REBOUND BACK CLOSER TO NORMAL...IN THE
60S.

.LONG TERM...SOME CHANGES TO THE EXTENDED FORECAST THIS MORNING WITH
THE ECMWF TRENDING TOWARD THE WARMER AND DRIER GFS SOLUTION OVER
THE WEEKEND. HAVE GONE AHEAD AND TAKEN THE SHOWERS OUT OF THE
FORECAST FOR SATURDAY AND SUNDAY AND WARMED THE HIGH TEMPERATURES BY
5 DEGREES OR SO. UPPER LEVEL RIDGE OFFSHORE ON FRIDAY MOVING OVER
WESTERN WASHINGTON ON SATURDAY AND REMAINING OVER THE AREA ON
SUNDAY. WARMER LOCATIONS OVER THE WEEKEND WILL SEE HIGHS IN THE MID
70S WITH MID 60S TO LOWER 70S COMMON. MODEL SOLUTIONS WIDELY
DIFFERENT FOR MONDAY WITH THE GFS KEEPING THE RIDGE OVER THE AREA
AND THE ECMWF BRINGS A TROUGH INTO WESTERN WASHINGTON. GFS MOS HIGH
TEMP FOR SEATTLE ON MONDAY IS 77...ECMWF 62. CURRENT FORECAST
MATCHES UP WITH THE ECMWF AND CLIMATOLOGY. NOT WILLING TO CHANGE DAY
7 FORECAST YET BUT WITH THE ECMWF TRENDING MORE TOWARD THE GFS
SOLUTION CONFIDENCE IN THE SUNDAY NIGHT AND MONDAY FORECAST IS LOW.
FELTON

&&

.AVIATION...MOIST UNSTABLE AIR WILL GIVE WESTERN WASHINGTON SHOWERS
AND ISOLATED THUNDERSTORMS AS A TROUGH MOVES OVER THE REGION TODAY.
THE MOUNTAINS WILL BE MOSTLY OBSCURED.

KSEA...SCATTERED SHOWERS WILL MOVE THROUGH THE AREA TODAY AND THERE
IS A RISK OF A THUNDERSTORM THIS AFTERNOON...ESPECIALLY IF A PSCZ
DEVELOPS.

&&

.MARINE...ONSHORE FLOW WILL CONTINUE AS A TROUGH MOVES OVER THE AREA
TODAY. THE SWELL OVER THE COASTAL WATERS WILL BE AROUND 10 FEET
TODAY. FOR THE PUGET SOUND AREA THERE IS A CHANCE OF A CONVERGENCE
ZONE AND WE MAY SEE ISOLATED THUNDERSTORMS. STARTING MIDWEEK THERE
WILL BE A RIDGE OF HIGH PRESSURE THAT BUILDS JUST OFFSHORE WITH NW
FLOW OVER THE AREA.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY COASTAL WATERS AND GRAYS HARBOR BAR.

&&

$$

WWW.WEATHER.GOV/SEATTLE

YOU CAN SEE AN ILLUSTRATED VERSION OF THIS FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML








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