Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 050335
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 PM PDT MON MAY 4 2015

.SYNOPSIS...A COLD FRONT OVER WESTERN WASHINGTON WILL BRING
SCATTERED SHOWERS TO THE AREA TONIGHT...AND ITS UPPER LOW WILL BRING
MORE SHOWERS AND A CHANCE OF THUNDERSTORMS TUESDAY. THE LOW WILL
MOVE AWAY WEDNESDAY FOR A TREND TOWARD SUNNIER AND WARMER WEATHER
THROUGH THE END OF THE WEEK. ANOTHER UPPER TROUGH WILL MOVE INTO THE
REGION LATE THIS WEEKEND OR EARLY NEXT WEEK FOR A CHANCE OF SHOWERS.

&&

.SHORT TERM...A WEAK COLD FRONT IS MOVING SLOWLY ACROSS WESTERN
WASHINGTON THIS EVENING. AT 8 PM THE FRONT WAS STILL WEST OF SEATTLE
AS IT WAS MOVING INTO THE WEST PART OF THE PUGET SOUND REGION. ITS
PRECIPITATION BAND IS FAR FROM SOLID...AND IT IS BRINGING SCATTERED
SHOWERS ALONG WITH BREEZY SOUTH TO SOUTHWEST WINDS TO MOST OF THE
FORECAST AREA. TEMPERATURES AT 8 PM WERE IN THE UPPER 40S AND 50S.

THE FRONT SHOULD MOVE ACROSS THE CASCADES AROUND MIDNIGHT...AND
WINDS OVER WESTERN WASHINGTON SHOULD GRADUALLY EASE BEHIND THE
FRONT. THE CLOSED UPPER TROUGH CURRENTLY CENTERED NEAR 50N/130W WILL
MOVE OVER VANCOUVER ISLAND LATE TONIGHT...AND THEN CONTINUE EASTWARD
ACROSS SOUTHERN BRITISH COLUMBIA TUESDAY AND TUESDAY NIGHT. THE AIR
MASS WILL REMAIN SOMEWHAT MOIST...AND IT WILL BECOME UNSTABLE
ESPECIALLY DURING THE AFTERNOON AND EVENING HOURS. SHOWERS WILL
CONTINUE...AND THERE WILL BE A CHANCE OF THUNDERSTORMS TOO.

THE UPPER LOW WILL DROP ALMOST DUE SOUTH ALONG THE WASHINGTON AND
OREGON CASCADES ON WEDNESDAY...WITH AN UPPER RIDGE NOSING EASTWARD
INTO BRITISH COLUMBIA ON THE NORTH SIDE OF THE UPPER LOW. THE AIR
MASS OVER WESTERN WASHINGTON WILL BEGIN DRYING AND STABILIZING ONCE
THE UPPER LOW MOVES SOUTH...BUT THERE WILL STILL BE A CHANCE OF
SHOWERS WEDNESDAY. THE LOW WILL CONTINUE SOUTH OVER THE SIERRA
NEVADA OF CALIFORNIA ON THURSDAY...WITH DRIER AND MORE STABLE
NORTHERLY FLOW OVER WESTERN WASHINGTON FOR A MOSTLY SUNNY DAY.
MCDONNAL

.LONG TERM...HERE IS THE LONG TERM SECTION FROM THE AFTERNOON
FORECAST DISCUSSION -- AN UPPER RIDGE WILL PREVAIL OVER THE REGION
ON FRI FOR DRY AND WARM CONDITIONS. BEYOND FRI...IT LOOKS LIKE A
HIGH LATITUDE BLOCK WILL DEVELOP...AND THIS WILL RESULT IN AN UPPER
LOW DEVELOPING OFF OUR COAST. THIS LOW WILL EVENTUALLY BECOME
CUT-OFF AND BECOME A WEATHER PERSONS WOE. CONSEQUENTLY...HAVE KEPT A
THREAT OF SHOWERS IN THE FORECAST DURING MUCH OF THIS PERIOD.

&&

.AVIATION...THE AIR WILL MOISTEN AND BECOME UNSTABLE TONIGHT AND
TUESDAY AS A TROUGH MOVES OVER THE REGION. THERE WILL BE SHOWERS AND
ISOLATED THUNDERSTORMS THROUGH TUESDAY NIGHT. THE MOUNTAINS WILL BE
MOSTLY OBSCURED.

KSEA...SCATTERED SHOWERS TRACKING THROUGH WESTERN WA HAVE NOT MOVED
INTO THE METRO AREA...BUT BY TUESDAY AFTERNOON THERE IS A GOOD
CHANCE OF SHOWERS AND A RISK OF A TSTM...ESPECIALLY IF A PSCZ
DEVELOPS.

&&

.MARINE...ONSHORE FLOW WILL CONTINUE AS A TROUGH MOVES OVER THE AREA
THROUGH TUESDAY. A WLY SWELL AROUND 10 FT SHOULD REACH THE COASTAL
WATERS TONIGHT. FOR THE PUGET SOUND AREA...THERE IS A CHANCE OF A
PUGET SOUND CONVERGENCE TUE AFTERNOON AND WE MAY SEE ISOLATED TSTMS
WITH THAT. 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 ADVISORIES ARE IN EFFECT FOR THE COASTAL
     WATERS...CENTRAL/EASTERN STRAIT OF JUAN DE FUCA...PUGET
     SOUND/HOOD CANAL AND GRAYS HARBOR BAR.

&&

$$

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




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