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000
FXUS66 KSEW 121634
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
930 AM PDT SUN MAY 12 2013

.SYNOPSIS...A COLD FRONT IS OVER WESTERN WASHINGTON TODAY AND RAIN
BANDS OR SHOWERS WILL OCCASIONALLY MOVE THROUGH WESTERN WASHINGTON.
ANOTHER WEATHER SYSTEM WILL REACH THE AREA MONDAY WITH RAIN TURNING
TO SHOWERS WITH ISOLATED THUNDERSTORMS. COOL UNSETTLED WEATHER WILL
PERSIST THROUGH THE WEEK AND INTO NEXT WEEKEND.

&&

.SHORT TERM...A COLD FRONT IS HUNG UP OVER THE REGION. THERE ARE
SOME RAIN BANDS AND SHOWERS ON RADAR EXTENDING SOUTHWEST OFF THE
COAST AND THESE WILL KEEP WESTERN WA DAMP THROUGH TONIGHT. A MORE
VIGOROUS UPPER SHORTWAVE TROUGH IS OUT AROUND 47N 147W THIS
MORNING...AND THIS WILL MOVE THROUGH THE BROAD UPPER TROUGH OFFSHORE
TODAY AND TONIGHT AND REACH WESTERN WA DURING THE DAY MONDAY. THE
AIR ALOFT HASN`T COOLED A GREAT DEAL YET BUT THE FREEZING LEVEL WILL
FALL SLOWLY THROUGH TONIGHT AND THEN MORE SHARPLY ON MONDAY. UPPER
HEIGHTS FALL OFF TO AROUND 550DAM WITH THE TROUGH AXIS LATE MON
AFTERNOON. SHOWERS MONDAY NIGHT WILL DRY UP IN WEAK RIDGING TUE.

.LONG TERM...UPPER HEIGHTS RISE TO AROUND 564DAM WITH WEAK RIDGING
TUESDAY...BUT THEN THE 12Z GFS MOVES HEIGHTS DOWN 60M THROUGH WED
AND THU MORNING AS WEAK DISTURBANCES IN THIS WEATHER PATTERN BRING A
LITTLE RAIN OR SHOWERS TO THE AREA AT TIMES. HEIGHTS STAY FAIRLY LOW
THROUGH THE END OF THE WEEK WITH A WEAKENING UPPER TROUGH ALONG THE
WEST COAST BUT THERE IS ANOTHER SURGE OF STRONGER ZONAL FLOW WORKING
ACROSS THE NORTH PACIFIC LATE IN THE WEEK. THE NEXT SIGNIFICANT
SHORTWAVE TROUGH IN THE 12Z GFS ARRIVES SAT NIGHT/SUN MORNING. WILL
SEE WHAT THE 12Z ECMWF SHOWS BUT I THINK IF I WERE CAMPING THIS WEEK
I WOULD WANT TO HAVE BLUE TARPS...BUT HERE IN THE METRO AREA WE
MIGHT NOT SEE MORE THAN PERIODS OF LIGHT SCATTERED SHOWER ACTIVITY.

&&

.AVIATION...A LONGWAVE UPPER TROUGH AXIS IS LOCATED NEAR 140W...WITH
MODERATE SW FLOW ALOFT OVER WRN WA. A FRONTAL BOUNDARY WAS LOCATED
JUST OFF THE COAST THIS MORNING...ALIGNED WITH THE FLOW ALOFT. THE
FRONT HAS SPREAD RAIN AND SHOWERS ACROSS WRN WA THIS MORNING...BUT
PRECIP WILL DECREASE IN COVERAGE THIS AFTN AND EVNG AS THE FRONT
BECOMES MORE DIFFUSE. HOWEVER...A MURKY AIR MASS WILL MEAN AREAS OF
IFR AND MVFR CIGS...MOST NOTABLY ALONG THE COAST AND OVER THE NORTH
INTERIOR. ON MON...A SHARP UPPER TROUGH WILL PASS WRN WA LATE IN THE
AFTN. LOTS OF LIFT ACTING ON A MOIST AND UNSTABLE AIR MASS COULD
LEAD TO A FEW THUNDERSTORMS ON MON AFTN AND EVNG.

KSEA...RAIN AND SHOWERS CONTINUING AT TIMES UNTIL ABOUT 03Z...THEN
TAKING A BREAK TONIGHT. MVFR CIGS IN THE 020-030 RANGE WILL PREVAIL
THROUGH TONIGHT. ON MONDAY...A SHARP UPPER TROUGH WILL
ARRIVE...LEADING TO AN INCREASINGLY MOIST AND UNSTABLE AIR
MASS...AND THE POSSIBILITY OF THUNDERSTORMS LATE IN THE AFTN. SFC
WINDS REMAINING SOUTHERLY.      HANER

&&

.MARINE...A COLD FRONT LOCATED JUST OFF THE COAST WILL CONTINUE TO
DISSIPATE...AFTER MOVING ONSHORE THIS AFTN. LOCAL AREAS OF SMALL
CRAFT SOUTHERLIES (NEAR SHORE COAST...PUGET SOUND...ADMIRALTY INLET)
WILL EASE THIS AFTN AND EVNG.

A STRONG SURFACE TROUGH WILL SWEEP ACROSS THE WATERS MONDAY
AFTERNOON AND EVENING. THIS FEATURE COULD BE ACCOMPANIED BY ISOLATED
THUNDERSTORMS MONDAY AFTERNOON...AND WILL BE FOLLOWED BY A STRONG
PUSH OF SW-W GRADIENTS LATE MONDAY AFTERNOON AND MONDAY NIGHT. AT
THIS TIME RATHER WIDESPREAD SMALL CRAFT ADVISORY SW-W WINDS ARE
EXPECTED ACROSS MOST WATERS LATER MONDAY INTO MONDAY NIGHT.

HIGH PRES WILL BUILD BACK INTO THE WATERS ON TUESDAY. A WEAKER
FRONTAL SYSTEM IS EXPECTED TO MOVE INTO THE COASTAL WATERS GIVING
POSSIBLE  SMALL CRAFT ADVISORY CONDITIONS THERE TUESDAY NIGHT INTO
WEDNESDAY.      HANER/ALBRECHT

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY INNER COASTAL WATERS NORTH OF POINT
        GRENVILLE UNTIL 3 PM TODAY.
     SMALL CRAFT ADVISORY PUGET SOUND AND HOOD CANAL...AND
        ADMIRALTY INLET THROUGH 3 PM TODAY.

&&

$$

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