Gale Watch 23, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
1024 AM PDT SAT MAR 31 2012

.SYNOPSIS...A VIGOROUS LOW PRESSURE SYSTEM OFF THE OREGON COAST WILL
WEAKEN AND MOVE NORTH DURING THE DAY TODAY FOR LOCALLY GUSTY WINDS
AND HEAVY RAIN. EXPECT THIS SYSTEM TO MOVE ACROSS THE AREA TONIGHT.
A FAST MOVING DISTURBANCE WILL MOVE ACROSS THE REGION ON SUNDAY.
EXPECT A MUCH WETTER SYSTEM TO IMPACT THE REGION ON MONDAY FOR THE
POSSIBILITY OF SIGNIFICANT RAINFALL ON THE SOUTHWEST FACING SLOPES
OF THE OLYMPICS AND NORTH CASCADES.

&&

.SHORT TERM...
A VIGOROUS LOW PRES SYSTEM WAS OFF THE OREGON COAST THIS MORNING.
THIS SERVED TO TIGHTEN THE NLY SFC PRES GRADIENT ACROSS THE CWA FOR
LOCALLY GUSTY N WINDS. THE FORECAST WAS UPDATED TO BUMP UP WIND
SPEEDS ACROSS SOME ZONES. IN ADDITION TO THE WIND...THE AIR MASS WAS
COLD ENOUGH SUCH THAT SOME LOWLAND ZONES HAVE RECEIVED A MIXTURE OF
RAIN AND SNOW THIS MORNING. EXPECT THE NLY PRES GRADIENT TO RELAX
THIS AFTERNOON.

LIGHTNING STRIKES HAVE BEEN OBSERVED OFF THE OREGON COAST THIS
MORNING. THIS ACTIVITY SHOULD REMAIN S OF THE CWA BUT CANNOT RULE
OUT A RANDOM ISOLATED STRIKE OVER THE CENTRAL COASTAL WATERS TODAY.

MEANWHILE...THE UPPER LOW OFF THE OREGON COAST WILL WEAKEN DURING
THE DAY AND OPEN UP INTO A TROF THIS EVENING. THE TROF WILL THEN
MOVE ACROSS THE AREA OVERNIGHT. THE STEADY PRECIP SHOULD TAPER OFF
TO SHOWERS LATER TODAY OR EARLY THIS EVENING...WITH SHOWERY WEATHER
CONTINUING OVERNIGHT. THE MODELS WERE HINTING THAT A PUGET SOUND
CONVERGENCE ZONE WILL DEVELOP LATE TONIGHT IN RESPONSE TO INCREASED
ONSHORE FLOW. THE NAM PLACES THIS FEATURE IN ITS TYPICAL LOCATION
NEAR THE KING/SNOHOMISH COUNTY LINE WHEREAS THE GFS WAS FARTHER N.

A FAST-MOVING SHORT WAVE TROF...EMBEDDED IN THE WESTERLY FLOW
ALOFT...WILL MOVE ACROSS THE REGION ON SUNDAY. THE LOW LEVEL ONSHORE
GRADIENT WILL REMAIN TIGHT FOR BREEZY CONDITIONS.

THE NEXT...MUCH WETTER SYSTEM...WILL BEGIN TO IMPACT THE CWA ON MON.
THE MODELS APPEARED TO BE HAVING SOME TIMING ISSUES WITH THIS
SYSTEM. CURRENTLY...LEANING TOWARD THE SLOWER ECMWF TIMING AS THESE
TYPE OF SYSTEMS END UP SLOWER THAN EXPECTED. AT ANY RATE...THIS
SYSTEM HAS THE POTENTIAL FOR PRODUCING SIGNIFICANT RAINFALL ON THE
SW FACING SLOPES OF THE OLYMPICS AND N CASCADES.

.LONG TERM FROM THE PREV DISCUSSION...
A BAROCLINIC BAND MAY STALL OVER THE AREA ON TUE...BRINGING HEAVY
RAIN TO THE AREA...ESPECIALLY THE COAST...OLYMPICS AND NORTH
CASCADES. THERE IS PLENTY OF JUICE WITH THIS SYSTEM. HOWEVER...
THERE ARE SOME BIG TIMING ISSUES BETWEEN THE MODELS. THE GFS IS 12
HRS FASTER THAN THE EURO. WILL WAIT A FEW MORE MODEL RUNS TO SEE
WHAT ALL SHAKES OUT BUT A BLEND IS THE RIGHT WAY TO GO FOR NOW. AT
THIS POINT POSSIBLE IMPACTS WOULD BE RIVER FLOODING ON THE SKOKOMISH
AND HEAVY SNOW IN THE NORTH CASCADES.

THE AIR MASS ACROSS WESTERN WA WILL REMAIN COOL AND UNSTABLE FROM
MID WEEK ONWARDS AS A BROAD UPPER LEVEL TROUGH SETTLES IN. SO EXPECT
ISOLATED TO SCATTERED SHOWERS EACH DAY WITH TEMPS BELOW CLIMO. THE
MODELS ARE HINTING TOWARD DRIER WEATHER NEXT WEEKEND AS A RIDGE
DEVELOPS OFFSHORE. BUT WON/T MAKE DRASTIC CUTS TO THE FORECAST JUST
YET. 33

&&

.HYDROLOGY...
A FLOOD WARNING FOR THE CHEHALIS RIVER AT GRAND MOUND WAS REPLACED
WITH AN ADVISORY DUE TO THE FACT THAT THE RIVER CONTINUES TO RUN
JUST BELOW FLOOD STAGE. EXPECT THIS RIVER TO CONTINUE TO SLOWLY
RECEDE. A FLOOD WATCH WAS STILL IN EFFECT FOR THE CHEHALIS RIVER
AT PORTER IN GRAYS HARBOR COUNTY.

THE NEXT SYSTEM TO KEEP AN EYE ON WILL BE THE MON/TUE SYSTEM. THIS
SYSTEM HAS THE POTENTIAL FOR PRODUCING SIGNIFICANT RAINFALL ON THE
SW FACING SLOPES OF THE OLYMPICS AND N CASCADES. THE CURRENT
FORECAST HAS 2 TO 4 INCHES OF RAIN IN THE 36-HR PERIOD ENDING AT 5
PM PDT TUE...HOWEVER THE POSSIBILITY EXISTS FOR HEAVIER AMOUNTS
ESPECIALLY IF THE FRONTAL BAND ENDS UP STALLING OVER THE AREA. THE
SKOKOMISH RIVER WILL BE THE MOST LIKELY RIVER TO FLOOD BUT CANNOT
RULE OUT SOME OTHER AREA RIVERS SINCE THE SOIL WILL LIKELY BE
NEARLY...IF NOT ALREADY...SATURATED BY THE TIME THIS SYSTEM ARRIVES.

BEYOND TUE...IT APPEARED THAT THE WEATHER PATTERN WILL TREND TOWARD
DRIER CONDITIONS FOR WRN WA.

&&

.AVIATION...STRONG SW FLOW ALOFT WITH N-E FLOW AT THE SURFACE. A
COMPLEX LOW PRES SYSTEM LIFTING NE FROM OFF THE OREGON COAST WILL
CONTINUE TO PRODUCE STEADY RAIN FOR THE REST OF THE MORNING. CIGS
WERE BOUNCING FROM MVFR TO LOCALIZED SPOTS WITH IFR. N-E WINDS WILL
BECOME S-SW EARLY THIS AFTERNOON BEHIND THE FRONT CURRENTLY ALONG
THE OR COASTLINE. THE AIR MASS WILL BECOME MORE UNSTABLE IN THE
AFTERNOON POST FRONTAL AND WILL PRODUCE SHOWERS THROUGH TONIGHT.
GENERAL IMPROVEMENT TREND AFTER THE STEADY RAIN TO MVFR/VFR CIGS
WITH SHOWERS THIS AFTERNOON AND EVENING. STRONG ONSHORE FLOW WILL
DEVELOP AFTER MIDNIGHT TONIGHT.

KSEA...NORTHERLY WIND 10-15 KNOTS SWITCHING TO SOUTHWEST 5 TO 10
KNOTS AROUND 21Z. CIGS BOUNCING DOWN INTO IFR DURING WITH RAIN
THROUGH AROUND NOON...THEN LIFTING TO 3-4K FT AROUND 20-21Z. DAMICO

&&

.MARINE...MAIN LOW PRESSURE CIRCULATION IS LOCATED 200 M WEST OF
NORTH BEND THIS MORNING...HOWEVER...A SECONDARY AREA OF LOW PRES HAS
DEVELOPED JUST OFF THE CENTRAL WA COAST. AS A RESULT STRONGER THAN
FCST EASTERLIES THROUGH THE STRAIT AND CHEHALIS GAP EXITING OVER THE
CENTRAL COAST HAVE DEVELOPED THIS MORNING. HAVE ISSUED SHORT FUSE
GALE WARNINGS NEAR THE WESTERN STRAIT OF JUAN DE FUCA...AND SCA FOR
NORTHERLY WINDS IN THE PUGET SOUND AND EASTERLIES FOR CENTRAL STRAIT
THROUGH EARLY THIS AFTERNOON.

THE MAIN LOW WILL WEAKEN LATER THIS AFTERNOON AS IT PASSES EAST INTO
THE CENTRAL OREGON COAST...EASING GRADIENTS AND WINDS. HOWEVER
STRONG SW ONSHORE GRADIENTS WILL INCREASE OVERNIGHT IN RESPONSE TO
BUILDING HIGH PRES ALONG THE COAST. STRONG SW SURGE THROUGH THE
INTERIOR AND WESTERLY SURGE THROUGH THE STRAIT SHOULD PICK UP AFTER
06Z...WITH A NEW ROUND OF SCAS AND POTENTIALLY GALES NEEDED.
GRADIENTS WILL EASE AS A WEAK DISTURBANCE PASSES THROUGH WESTERN WA
SUNDAY AFTERNOON.

A STRONG FRONTAL SYSTEM WILL MOVE THROUGH COASTAL WATERS SUNDAY
NIGHT OR MONDAY...EVENTUALLY BRINGING POSSIBLE GALES TO MOST WATERS.
DAMICO

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD ADVISORIES OR WATCHES ARE IN EFFECT FOR PARTS OF THE
     CWA.

PZ...GALE WARNING IN EFFECT FOR THE COASTAL WATERS FROM CAPE
     FLATTERY TO JAMES ISLAND OUT TO 10 NM UNTIL 1 PM PDT THIS
     AFTERNOON.

     SMALL CRAFT ADVISORIES ARE IN EFFECT UNTIL 6 PM PDT SUNDAY
     FOR THE NEAR SHORE WATERS FROM JAMES ISLAND TO POINT
     GRENVILLE OUT TO 10 NM...COASTAL WATERS...THE CENTRAL AND
     WESTERN STRAIT OF JUAN DE FUCA...AND THE PUGET SOUND/HOOD
     CANAL.

     SMALL CRAFT ADVISORY FOR ROUGH BAR UNTIL 5 AM PDT SUNDAY
     FOR THE GRAYS HARBOR BAR.

&&

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