Small Craft Advisory 947, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
955 PM PDT SUN MAR 25 2012

.SYNOPSIS...A WEAKENING LOW PRESSURE SYSTEM OFF THE NORTHERN
CALIFORNIA COAST WILL MOVE ONSHORE LATER THIS EVENING...AND THEN
ACROSS THE AREA ON MONDAY. LOOK FOR A STRONGER SYSTEM TO IMPACT THE
REGION ON TUESDAY FOR RAIN AND MOUNTAIN SNOW. WET AND UNSETTLED
CONDITIONS WILL CONTINUE ON WEDNESDAY DUE TO AN UPPER LOW OFFSHORE
SENDING WAVES OF DISTURBANCES NORTHWARD ACROSS THE REGION.

&&

.SHORT TERM...WSR-88D'S SHOW RAIN EXTENDING FROM THE NORTHERN END OF
THE WILLAMETTE VALLEY THROUGH THE SOUTHWEST INTERIOR UP TO THE NORTH
COAST. THERE HAVE BEEN A FEW SPRINKLES IN THE SEATTLE METRO AREA BUT
THIS IS AS FAR NORTH AS THE RAIN HAS MOVED THIS EVENING. PRETTY
MESSY SITUATION TONIGHT INTO MONDAY MORNING WITH AN ELONGATED UPPER
LEVEL TROUGH ALONG THE WEST COAST. VORT MAX EMBEDDED IN THE
SOUTHERLY FLOW ALOFT MOVING OVER WESTERN WASHINGTON OVERNIGHT WITH
THE FLOW ALOFT SLIGHTLY DIFLUENT OVER THE AREA. WHILE THERE ISN'T
ANY PRECIPITATION BEING REPORTED IN WESTERN OREGON AND OVER THE
OREGON CASCADES SOUTH OF PORTLAND WITH THE DIFLUENT FLOW ALOFT
EXPECT SOME DEVELOPMENT OVER WESTERN WASHINGTON OVERNIGHT INTO EARLY
MONDAY MORNING. THIS WILL KEEP SHOWERS IN THE FORECAST. THE LAST
VORT LOBE ROTATES THROUGH MONDAY MORNING WITH A BRIEF BREAK IN THE
ACTION BEFORE A MORE ORGANIZED FRONT APPROACHES THE AREA MONDAY
EVENING. RIGHT NOW THIS FRONT IS LOCATED NEAR 137W WITH THE PARENT
LOW BACK NEAR 46N/141W. SATELLITE IMAGERY SHOWS THE PARENT LOW
MOVING SOUTH. IN ADDITION THERE IS AT LEAST ONE WAVE FORMING ALONG
THE BACKSIDE OF THE FRONT. BOTH OF THESE VARIABLES WILL WEAKEN AND
SLOW THE FRONT EASTWARD MOVEMENT DOWN TONIGHT INTO MONDAY. BOTH THE
GFS AND THE 00Z NAM INDICATING A NEGATIVELY TILTED FRONT MOVING INTO
WESTERN WASHINGTON TUESDAY MORNING. GIVEN THE CURRENT SATELLITE
IMAGERY THIS SLOW PREDICTED EASTWARD MOVEMENT LOOKS GOOD. COLD UPPER
LEVEL TROUGH REMAINING OFF THE COAST FOR THE REMAINDER OF TUESDAY
KEEPING PRECIPITATION IN THE FORECAST. CURRENT FORECASTS HAS THE
TRENDS COVERED. NO CHANGES TO THE FORECAST THIS EVENING. FELTON

.LONG TERM...PREVIOUS DISCUSSION FOLLOWS.
A WET AND ACTIVE PATTERN WILL PERSIST...ALTHOUGH THERE MIGHT BE SOME
RETROGRESSION OF THE LONG WAVE FEATURES LATE IN THE PERIOD. IT
APPEARED THAT THE WED NIGHT/THU TIME FRAME WILL BE THE WETTEST
PERIOD. ELEVATIONS ABOVE 3K COULD RECEIVE 1-3 FT OF SNOW BY EARLY
FRI. THERE WILL ALSO BE LOCALLY HEAVY RAIN AT TIMES ACROSS THE LOWER
ELEVATIONS...ESPECIALLY ON THE COAST AND THE LOWER SW FACING SLOPES
OF THE OLYMPIC RANGE. IT WILL ALSO BE WINDY AT TIMES...ESPECIALLY
OVER THE COAST AND NW INTERIOR. ANTICIPATE BELOW NORMAL DAYTIME
TEMPS AND ABOVE CLIMO POPS DURING THIS PERIOD.

&&

.CLIMATE...WITH A HIGH OF 56 DEGREES AT SEA-TAC AIRPORT TODAY THIS
WAS THE SECOND CONSECUTIVE DAY WITH AN ABOVE NORMAL HIGH
TEMPERATURE. THE LAST TIME THERE WAS BACK TO BACK ABOVE NORMAL HIGHS
IN SEATTLE WAS FEBRUARY 9TH AND 10TH. FELTON

&&

.HYDROLOGY...
A SERIES OF WET SYSTEMS WILL IMPACT THE CWA THROUGH DAY 7 BUT THE
HEAVIEST PRECIP IS EXPECTED TO FALL ABOUT MIDWEEK OR DURING THE TUE
NIGHT THRU THU NIGHT TIME FRAME. THE SNOW LEVELS WILL BE LOW ENOUGH
SUCH THAT MOST OF THE PRECIP WILL FALL AS SNOW IN THE MOUNTAINS.
HOWEVER THE SNOW LEVELS WILL OCCASIONALLY AND BRIEFLY POP UP ABOVE
4K FT AT TIMES. STRONG SLY OR SW FLOW WILL RESULT IN HEAVY RAIN AT
TIMES ON THE CORRESPONDING LOWER FACING SLOPES OF THE OLYMPICS AND
CASCADES. THIS WILL RESULT IN RAPID RISES ON SOME RIVERS BY THE END
OF THE WEEK. IT IS POSSIBLE THAT THE SKOKOMISH COULD APPROACH FLOOD
STAGE BY THE END OF THE WEEK.

&&

.AVIATION...AN UPPER LEVEL TROUGH WILL PASS THROUGH WESTERN WA
TONIGHT. SHOWERS WILL SPREAD NORTH THROUGH MON MORNING. THE AIR MASS
WILL REMAIN MOIST AS WEAK SOUTHERLY ONSHORE FLOW DEVELOPS...WILL
LIKELY SEE MVFR CONDITIONS. EXPECT MAINLY DRY CONDITIONS LATE
MORNING THROUGH THE AFTERNOON WITH VFR CONDITIONS. 33

KSEA...SHOWERS WILL SPREAD NORTH TONIGHT WITH MVFR CONDITIONS
EXPECTED...S WINDS AT THE SURFACE. CIGS WILL LIFT LATE MON MORNING
FOR VFR CONDITIONS AND MAINLY DRY WEATHER. 33

&&

.MARINE...A WEAK SYSTEM WILL PASS THROUGH WESTERN WA TONIGHT WITH
LIGHT SOUTHERLY ONSHORE FLOW DEVELOPING. SOUTH WINDS WILL INCREASE
ON MON AS A COLD FRONT APPROACHES THE COAST. THIS SYSTEM WILL MOVE
INLAND MON NIGHT. A GALE WATCH REMAINS IN EFFECT FOR THE COASTAL
WATERS AND STRAIT OF JUAN DE FUCA. A BROAD AREA OF LOW PRES WILL
REMAIN OVER THE NE PAC THROUGH THE END OF THE WEEK...WHILE A SERIES
OF FRONTS PASS THROUGH THE REGION. THE PATTERN WILL REMAIN ACTIVE
WITH SMALL CRAFT ADVISORIES OR GALES FORECAST EACH DAY. 33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY COASTAL WATERS THROUGH MON AFTERNOON.
     GALE WATCH IN EFFECT MON NIGHT AND TUE FOR THE COASTAL WATERS
      AND STRAIT OF JUAN DE FUCA.

&&

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