Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 060338 CCA
AFDSEW

AREA FORECAST DISCUSSION...CORRECTION TO TEMPERATURES IN SHORT TERM
NATIONAL WEATHER SERVICE SEATTLE WA
900 PM PDT TUE MAY 5 2015

.SYNOPSIS...AN UPPER LEVEL LOW OVER WESTERN WASHINGTON TONIGHT WILL
PRODUCE SCATTERED SHOWERS AND EVENING THUNDERSTORMS. THE LOW WILL
MOVE OFF TO THE SOUTH AND EAST ON WEDNESDAY WITH SHOWERS DECREASING
IN COVERAGE. AN UPPER LEVEL RIDGE WILL BUILD OFF THE COAST FRIDAY
AND MOVE OVER WESTERN WASHINGTON BY THE WEEKEND GIVING SUNSHINE AND
WARMER TEMPERATURES. UNSETTLED WEATHER WILL RETURN EARLY NEXT WEEK.

&&

.SHORT TERM...THERE IS AN UPPER LOW CENTER RIGHT OVER WESTERN
WASHINGTON THIS EVENING...SITUATED IN THE SOUTHWEST PORTION OF THE
LARGER UPPER TROUGH. THIS FEATURE PRODUCED SOME THUNDERSTORMS WITH
SMALL HAIL THIS AFTERNOON AND EARLY THIS EVENING...BUT WE HAVE HAD
JUST SCATTERED SHOWERS ACROSS THE FORECAST AREA SINCE A LITTLE AFTER
6 PM. THERE IS A POORLY ORGANIZED PUGET SOUND CONVERGENCE ZONE AS
WELL...AND SOME OF THE HEAVIEST RAINFALL THIS EVENING HAS OCCURRED
OVER SEATTLE. THE SNOW LEVEL IS AROUND 3000 TO 3500 FT THIS
EVENING...AND LOWLAND TEMPERATURES AT 8 PM WERE IN THE MID 40S TO
LOWER 50S.

THE UPPER TROUGH...WHICH EXTENDS NORTHEAST FROM THE NORTHERN OREGON
OFFSHORE WATERS ACROSS WESTERN WASHINGTON INTO THE CANADIAN
ROCKIES...WILL SHIFT SLOWLY SOUTHEAST TONIGHT AND THEN TRACK CLOSER
TO DUE SOUTH ON WEDNESDAY. BY LATE WEDNESDAY THE MAIN LOW CENTER
SHOULD BE OVER THE SOUTHERN OREGON CASCADES...WITH DRIER NORTHERLY
FLOW STARTING TO DEVELOP OVER WESTERN WASHINGTON. THE AIR MASS WILL
REMAIN UNSTABLE INTO WEDNESDAY AFTERNOON THOUGH...OR EVEN WEDNESDAY
EVENING OVER THE CASCADES. SCATTERED SHOWERS WILL CONTINUE AND THERE
WILL STILL BE A CHANCE OF THUNDERSTORM. PRECIPITATION AMOUNTS SHOULD
BE GENERALLY LIGHT.

DRY NORTH TO NORTHEAST FLOW WILL PREVAIL OVER WESTERN WASHINGTON
WEDNESDAY NIGHT AND THURSDAY...WITH THE UPPER LOW MOVING FURTHER
SOUTH OVER CALIFORNIA. THURSDAY SHOULD BE DRY AND MOSTLY SUNNY WITH
HIGH TEMPERATURES MAINLY 60 TO 70 DEGREES. FRIDAY WILL BE SUNNY AND
WARMER YET AS DRY NORTHERLY FLOW CONTINUES...WITH THE OFFSHORE UPPER
RIDGE MOVING INSIDE OF 130W AND ONSHORE FLOW WEAKENING.   MCDONNAL

.LONG TERM...HERE IS THE LONG TERM SECTION FROM THE AFTERNOON
FORECAST DISCUSSION -- MODELS HAVE TRENDED EVEN STRONGER WITH THE
RIDGE CENTERED OVER THE PAC NW ON SATURDAY. THE FLOW IS LIGHT AND IT
SHOULD WARM UP FURTHER. WENT WITH A BLEND OF MOS WHICH INDICATES MID
AND UPPER 70S ACROSS WRN WA BUT A COUPLE SPOTS COULD MAKE A RUN AT
80. HIGH PRESSURE STARTS TO SHIFT EWD ON SUNDAY BUT IT SHOULD
PROVIDE ANOTHER DRY AND WARM DAY. HIGHS WILL AGAIN BE IN THE 70S
WITH JUST SOME HIGH CLOUDS AS A TROUGH APPROACHES.

THE GFS BRINGS AN ELONGATED N/S ORIENTED TROUGH ALONG THE COAST
SUNDAY NIGHT. MODELS DIFFER ON HOW THIS LOW EVOLVES BUT IT SHOULD
BECOME CUT OFF NEAR THE PAC NW COAST. IF THE LOW GOES TOO FAR
S...PRECIPITATION COULD BYPASS WRN WA. HOWEVER...MOST MODELS BRING
THE LOW ON A TRACK FAVORABLE FOR SHOWERS AND EVEN THUNDERSTORMS
MONDAY AND TUESDAY. HIGHS WILL BE COOLER IN THE UPPER 50S TO MID
60S. MERCER

&&

.AVIATION...AN UPPER LEVEL LOW OVER THE REGION WILL SAG SOUTH TO
OREGON THROUGH WEDNESDAY. THERE AIR IS MOIST AND SOMEWHAT UNSTABLE
WITH SHOWERS THIS EVENING...ESPECIALLY IN THE PUGET SOUND AREA.
LIGHT FLOW ALOFT WILL BECOME NORTHERLY WEDNESDAY. AFTER AREAS OF
MORNING CLOUDS ON WEDNESDAY THE AFTERNOON HEATING SHOULD CAUSE
SCATTERED SHOWERS TO BUILD UP.

KSEA...SHOWERS AROUND PUGET SOUND WILL OCCASIONALLY AFFECT SEATTLE
THROUGH THE MIDDLE OF THE NIGHT. AREAS OF LOW CLOUDS ARE A GOOD BET
WEDNESDAY MORNING...THEN AFTERNOON CUMULUS BUILDUPS WILL KEEP A FEW
SHOWERS IN THE FORECAST.

&&

.MARINE...A TROUGH WILL WEAKEN AND FILL OVER THE REGION THROUGH
WEDNESDAY AS THE UPPER LEVEL TROUGH SAGS SOUTH. A RIDGE OF HIGH PRES
WILL DEVELOP ALONG 130W STARTING LATER WED AND SHOULD REMAIN IN
PLACE THROUGH THE END OF THE WEEK. EXPECT MODERATE NW FLOW TO
DEVELOP EACH DAY WITH A PRETTY GOOD AFTERNOON AND EARLY EVENING SEA
BREEZE ALONG THE COAST AND IN THE STRAIT...AND THERE WILL PROBABLY
BE ENOUGH OF A BREEZE EACH AFTERNOON OVER THE INLAND WATERS FOR THE
SAILBOATS.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&

$$

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







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