Gale Warning 25, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
348 AM PST WED FEB 29 2012

.SYNOPSIS...A COLD UPPER LEVEL TROUGH WILL REMAIN OVER WESTERN
WASHINGTON THROUGH TONIGHT...WHICH WILL MAINTAIN RAIN AND SNOW
SHOWERS ACROSS THE AREA. THE UPPER LEVEL TROUGH WILL MOVE EAST
THURSDAY ALLOWING SHOWER ACTIVITY TO GRADUALLY DIMINISH THROUGH THE
EVENING. A WARM FRONT WILL SPREAD LIGHT RAIN OVER THE AREA ON FRIDAY
AND SATURDAY. A COLD FRONT WILL BRING RAIN ON MONDAY...FOLLOWED BY
POST-FRONTAL SHOWERS ON TUESDAY.

&&

.SHORT TERM...A COLD UPPER LEVEL LOW WILL REMAIN OVER W WA TODAY AND
TONIGHT. THE SNOW LEVEL WILL BE DOWN AROUND 500 FEET...SO RAIN AND
SNOW SHOWERS WILL REMAIN IN THE FORECAST. SHOWERS SHOULD BE
PREDOMINANTLY RAIN...BUT HEAVIER SHOWERS OR AREAS THAT RECEIVE MORE
PERSISTENT SHOWER ACTIVITY...OR HIGHER HILLS WILL BE MORE PRONE TO
SNOW SHOWERS. TEMPERATURES MAINLY IN THE UPPER 30S TO LOWER 40S WILL
QUICKLY MELT ANY SNOW. BOTH GFS/NAM HAD LIFTED INDICES DOWN TO -1
OVER THE COASTAL WATERS TODAY...AND OVER THE COASTAL ZONES AND THE
INTERIOR FROM ABOUT TACOMA SOUTHWARD THIS AFTERNOON. NAM BUFR
SOUNDINGS FOR OLYMPIA AND HOQUIAM SHOWED DEEP SKINNY CAPE OF AROUND
300 J/KG AND AN EQUILIBRIUM LEVEL WELL ABOVE THE -20C ISOTHERM FROM
ABOUT 20Z-00Z...SO THAT WAS JUST ENOUGH TO INCLUDE A CHANCE OF
THUNDERSTORMS IN THE FORECAST. IR IMAGERY SHOWS A LOT OF WELL
DEVELOPED CONVECTIVE CLOUDS JUST OFFSHORE AND A FEW LIGHTNING
STRIKES HAVE ALREADY SHOWN UP.

MODELS REMAIN IN GOOD AGREEMENT TAKING THE UPPER LEVEL TROUGH
EASTWARD ON THURSDAY...ALLOWING SHOWER ACTIVITY TO DIMINISH. SNOW
LEVELS WILL REMAIN LOW...SO A CHANCE OF SNOW SHOWERS WILL HAVE TO
STAY IN THE FORECAST.

THERE DOES NOT SEEM TO BE ANY PERIOD WHERE A CONVERGENCE ZONE IS
REALLY A GOOD POSSIBILITY. THERE MIGHT BE SOME POTENTIAL ON
THURSDAY...BUT THE MESOSCALE MODEL WINDS DO NOT SUPPORT IT STRONGLY.
THE NAM PRECIP FIELDS SUGGEST THERE MIGHT BE SOME ACTIVITY THAT
LOOKS LIKE A CONVERGENCE ZONE TONIGHT...BUT CAUSED BY W WINDS AT 850
MB-700 MB CREATING A WAKE DOWN STREAM FROM THE OLYMPICS.

THE 00Z/06Z MODELS ARE ALSO IN GOOD AGREEMENT WITH THE WARM
ADVECTION THAT DEVELOPS ON FRIDAY...COMING ACROSS THE TOP OF A BROAD
RIDGE OFFSHORE. THERE HAVE BEEN SOME CHANGES FROM THE MODEL RUN 24
HOURS AGO SO CONFIDENCE...WHILE STILL GOOD...IS JUST A BIT LESS THAN
FOR THURSDAY. W FLOW ALOFT IN THE MID LEVELS WILL PROBABLY PUT THE
GREATER PUGET SOUND REGION IN THE OLYMPIC RAIN SHADOW. KAM

.LONG TERM...AGREEMENT BETWEEN THE ECMWF AND GFS REMAINS FAIRLY GOOD
FOR THE SATURDAY-TUESDAY PERIOD. WARM ADVECTION CAUSED LIGHT RAIN
CONTINUES SATURDAY...STILL WITH PUGET SOUND IN THE OLYMPIC RAIN
SHADOW. THE WARMING TREND SHOULD BE ENOUGH TO BOOST HIGH
TEMPERATURES BACK TO THE LOWER 50S...WHICH IS NEAR NORMAL. THE RIDGE
AXIS SLIDES EAST OVER W WA SATURDAY NIGHT...AND THE RIDGE AMPLIFIES
JUST ENOUGH SUNDAY TO PUSH THE RAIN JUST ACROSS THE BORDER OVER
B.C.  THIS IS STILL TOO CLOSE BY TO GO WITH A DRY FORECAST...SO THE
SUNDAY FORECAST WILL STILL HAVE A CHANCE OF RAIN.

THE UPPER LEVEL RIDGE SLIDES EAST SUNDAY NIGHT...ALLOWING AN
OFFSHORE COLD FRONT TO MOVE INLAND ON MONDAY. GFS ADVERTISES THIS AS
A FAIRLY GOOD RAIN BUT ONLY LASTING ABOUT 12 HOURS AS THE FRONT
SLOWLY DRAGS ACROSS THE REGION. MOIST NW POST-FRONTAL FLOW ON
TUESDAY LOOKS A LITTLE UNSTABLE AND PRETTY COLD WITH 850 MB
TEMPERATURES NEAR -8C. THIS COULD DROP SNOW LEVELS BACK DOWN TO 500
FEET OR LESS FOR POSSIBLE SNOW SHOWERS. KAM

&&

.HYDROLOGY...FLOODING IS NOT EXPECTED THROUGH EARLY NEXT WEEK.

&&

.AVIATION...AN UPPER LEVEL TROUGH WILL SETTLE OVER THE AREA TODAY
AND TONIGHT. AT THE SURFACE...ONSHORE FLOW WILL PREVAIL. AIR MASS
MOIST AND UNSTABLE.

WITH THE UPPER TROUGH MOVING OVERHEAD TODAY...THE AIR MASS WILL BE
MARGINALLY UNSTABLE ENOUGH THAT A FEW THUNDERSTORMS CANNOT BE RULED
OUT NEAR THE COAST AND OVER THE SOUTHWEST INTERIOR.

KSEA...SHOWERS TODAY AND TONIGHT. THE AIR MASS IS JUST COLD ENOUGH
FOR A RAIN/SNOW MIX AT TIMES. NO ACCUMULATIONS ARE EXPECTED AT THE
TERMINAL. SOUTH WIND 10 TO 15 KNOTS. SCHNEIDER

&&

.MARINE...SMALL CRAFT ADVISORY SOUTHERLY WINDS SHOULD CONTINUE MOST
WATERS TODAY AND TONIGHT AS A SURFACE LOW NEAR VANCOUVER ISLAND
SLOWLY WEAKENS AND SHIFTS EAST. A FRONTAL SYSTEM WILL LIKELY BRING
ANOTHER ROUND OF SMALL CRAFT ADVISORY WINDS TO MOST WATERS FRIDAY
AND FRIDAY NIGHT. SCHNEIDER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY ALL WATERS.
    .SMALL CRAFT ADVISORY GRAYS HARBOR BAR FOR ROUGH CONDITIONS.

WWW.WEATHER.GOV/SEATTLE

FOR THE GRAPHICAL AFD...VISIT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SEATTLE WA
757 AM PST WED FEB 29 2012

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0756 AM     SNOW             5 NNW GRAND MOUND       46.88N 123.04W
02/29/2012  E0.0 INCH        THURSTON           WA   TRAINED SPOTTER

            VISIBILITY 1 1/2 MILE IN SNOW. LIGHT COATING.

&&

CERNIGLIA

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SEATTLE WA
818 AM PST WED FEB 29 2012

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0817 AM     SNOW             11 WSW BANGOR TRIDENT B 47.65N 122.94W
02/29/2012  M6.0 INCH        JEFFERSON          WA   TRAINED SPOTTER

            5.5 INCHES ON GROUND. 2 INCHES OVER THE LAST 2 HOURS. 31
            DEGREES. STILL SNOWING.

&&

CERNIGLIA