Small Craft Advisory 787, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 AM PDT SUN JUL 31 2011

.SYNOPSIS...A WEAK FRONT WILL MOVE THROUGH WESTERN WASHINGTON TODAY
FOR MOSTLY CLOUDY AND COOLER WEATHER WITH SOME LIGHT SHOWERS. A
PATTERN OF WEAK ONSHORE FLOW WILL PREVAIL NEXT WEEK FOR AFTERNOON
SUNSHINE...PATCHY NIGHT AND MORNING CLOUDS...AND NEAR NORMAL
TEMPERATURES.

&&

.SHORT TERM...A WEAK FRONT IS MOVING INTO THE NORTHWEST PART OF
WESTERN WASHINGTON EARLY THIS MORNING...AND ITS UPPER TROUGH IS
OFFSHORE ALONG 130W. THE FRONT HAS PRODUCED SPOTTY PRECIPITATION IN
THE NORTHWEST INTERIOR...WITH SOMEWHAT MORE ALONG THE NORTH COAST.
THE FRONT APPEARS TO HAVE RECENTLY MOVED THROUGH QUILLAYUTE...WHERE
0.17 INCH HAS FALLEN. IN ADDITION...LOW LEVEL ONSHORE FLOW THAT
DEVELOPED SATURDAY EVENING HAS BEEN PUSHING MARINE STRATUS INLAND
FROM THE COAST.

THE FRONT WILL WEAKEN A BIT AS IT CONTINUES EAST-SOUTHEASTWARD
ACROSS THE FORECAST AREA TODAY. BY THIS EVENING THERE SHOULD BE JUST
SOME LINGERING LIGHT SHOWERS ALONG THE WEST SLOPES OF THE CASCADES.
A WEAK PUGET SOUND CONVERGENCE ZONE COULD DEVELOP AS THE UPPER
TROUGH ARRIVES THIS AFTERNOON...BUT IT WILL LIKELY BE INSIGNIFICANT
AS FAR AS PRECIPITATION GOES. THE COMBINATION OF THE FRONTAL SYSTEM
AND ONSHORE FLOW WILL KEEP THE DAY MOSTLY CLOUDY...RELATIVELY
COOL...AND BRING A LITTLE PRECIPITATION TO MOST OF THE FORECAST
AREA.

THE UPPER TROUGH WILL MOVE EAST OF THE CASCADES TONIGHT...LEAVING
THE PACIFIC NORTHWEST IN A RATHER NONDESCRIPT PATTERN OF WEAK ZONAL
FLOW ALOFT AND WEAK ONSHORE FLOW AT LOW LEVELS MONDAY AND TUESDAY.
THIS PATTERN -- SIMILAR TO WHAT WE HAD MOST OF LAST WEEK -- WILL
RESULT IN TYPICAL HIGH SUMMER WEATHER. WE WILL HAVE GENERALLY SUNNY
DAYS WITH SOME LOW CLOUDS FORMING LATE NIGHT AND EARLY MORNINGS...
AND TEMPERATURES WILL BE CLOSE TO NORMAL.  MCDONNAL

.LONG TERM...THE PATTERN MENTIONED ABOVE WILL MOST LIKELY CONTINUE
THROUGH THE EXTENDED PERIOD WEDNESDAY TO SATURDAY. THAT IS NOT A
SURE BET HOWEVER...BECAUSE SOME RUNS OF BOTH THE GFS AND EUROPEAN
MODEL HAVE SHOWN A WEAK UPPER TROUGH MOVING THROUGH...MOST LIKELY
AROUND WEDNESDAY IF IT HAPPENS AT ALL. SO A MARINE PUSH IS NOT OUT
OF THE QUESTION AT SOME POINT DURING THE MIDDLE OR LATE PART OF THE
WEEK...BUT A FORECAST FOR SEASONAL WEATHER IS THE BEST BET AT THIS
TIME.  MCDONNAL

&&

.AVIATION...FRONT MOVING ONSHORE THIS MORNING. ONSHORE GRADIENTS
AHEAD OF THE FRONT PUSHED THE LOW STRATUS...CEILINGS NEAR 1000
FEET...ALONG THE COAST INTO THE INTERIOR FROM THE PUGET SOUND
NORTHWARD. 5000 FOOT DECK OUT AHEAD OF THE FRONT OVER THE TOP OF THE
STRATUS WHICH IS THE CEILINGS HEIGHTS OVER THE SOUTHWEST INTERIOR AT
10Z WITH THE LACK OF LOW STRATUS IN THE AREA. FRONT MOVING THROUGH
BY LATE MORNING WITH CEILINGS NEAR 1000 FEET BECOMING WIDESPREAD BY
15Z. BEHIND THE FRONT CONVERGENCE ZONE FORMING NEAR KPAE AND THE
EAST ENTRANCE TO THE STRAIT. CEILINGS NEAR 1000 FEET CONTINUING IN
THE VICINITY OF THE STRAIT UNTIL EARLY AFTERNOON. FOR THE REMAINDER
OF THE AREA CEILINGS IMPROVING UP TO THE LOW END OF VFR BY LATE
AFTERNOON. CLOUDS SCATTERING OUT THIS EVENING BUT WITH THE LOW LEVEL
ONSHORE FLOW STILL INTACT OVERNIGHT EXPECT AN MVFR STRATUS DECK TO
REFORM MONDAY MORNING.

KSEA...CEILINGS REMAINING NEAR 1000 FEET INTO THE MORNING HOURS
LIFTING UP TO NEAR 2000 FEET BY MIDDAY AND TO NEAR 3500 FEET BY 00Z
MONDAY. SOUTHWEST WINDS 6-10 KNOTS THROUGH THE AFTERNOON HOURS
SWITCHING TO NORTHWEST IN THE EVENING. FELTON

&&

.MARINE...ONSHORE FLOW WILL REMAIN THE DOMINANT FEATURE THROUGH THIS
WEEK...BETWEEN THE SURFACE HIGH OVER THE THE NORTHEAST PACIFIC AND A
SURFACE TROUGH OVER EASTERN WASHINGTON. A WEAKENING COLD FRONT WILL
MOVE THROUGH THE WATERS THIS MORNING. GALE FORCE WINDS IN THE
CENTRAL/EAST STRAIT OF JUAN DE FUCA WILL REDEVELOP THIS AFTERNOON AS
THE ONSHORE FLOW INCREASES BEHIND THE FRONT. THE PARTS OF THE NORTH
INLAND WATERS AND ADMIRALTY INLET ADJACENT TO THE STRAIT OF JUAN DE
FUCA WILL ALSO SEE SCA WINDS THIS AFTERNOON INTO THE EVENING HOURS.
WINDS WILL BE DIURNALLY DRIVEN FOR THE REMAINDER OF THE WEEK WITH
SMALL CRAFT ADVISORY WESTERLIES POSSIBLE IN THE CENTRAL AND EASTERN
STRAIT DURING THE EVENING HOURS. FELTON

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...GALE WARNING CENTRAL AND EAST STRAIT THIS EVENING.
     SMALL CRAFT ADVISORY ADMIRALTY INLET AND NORTH INLAND WATERS
      THIS EVENING.
     SMALL CRAFT ADVISORY CENTRAL AND EAST STRAIT SUNDAY
     GALE WATCH CENTRAL AND EAST STRAIT SUNDAY EVENING.

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