Napavine Weather Discussion

000
FXUS66 KSEW 100005 AAA
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA...UPDATED
350 PM PST TUE MAR 9 2010

UPDATED HYDRO SECTION

.SYNOPSIS...A FRONTAL SYSTEM WILL PUSH RAIN INLAND THIS EVENING. AS
THE RAIN BECOMES HEAVIER THE PRECIPITATION MAY MIX WITH
SNOW...MAINLY AROUND THE HOOD CANAL. SHOWERS WILL TAPER OFF
WEDNESDAY WITH SOME SUN BREAKS IN THE AFTERNOON. A SERIES OF
STRONGER SYSTEMS WILL AFFECT THE AREA BEGINNING LATE WEDNESDAY NIGHT
AND LASTING THROUGH FRIDAY. SHOWERS WILL BE IN PLACE FRIDAY NIGHT
AND SATURDAY...WITH SHORTWAVE RIDGING BUILDING OVERHEAD SATURDAY
NIGHT. A FRONTAL SYSTEM WILL STALL ALONG THE COAST ON SUNDAY.

&&

.SHORT TERM...SHORTWAVE RIDGING OVER THE AREA HAS SHIFTED EAST OF
THE CASCADES TODAY AND A SPLITTING FRONTAL SYSTEM IS POSITIONED
OFFSHORE. THE STRONG POLAR JET CAN IS DIVING TO THE SOUTHEAST
PUSHING THE BULK OF THE ENERGY WITH THE SYSTEM TOWARD THE OR/CA
BORDER. COLD FRONT IS LOCATED JUST OUTSIDE OF 125W.

LIGHT PRECIPITATION HAS ALREADY BEGUN ALONG THE COAST...BUT ONLY MID
AND HIGH LEVEL CLOUDS HAVE WORKED INLAND. LIGHT PRECIPITATION WILL
WORK INLAND LATER THIS EVENING. LOW LEVEL 1000-850 MB THICKNESSES
SUPPORT PRECIP MIXING WITH SNOW IN THE LATE EVENING AND EARLY
MORNING HOURS JUST ABOUT EVERYWHERE. HOWEVER PRECIP WILL NOT WORK
INTO THE NORTHWEST INTERIOR UNTIL LATER TONIGHT. COLDEST AIR WILL
POOL SE OF THE OLYMPICS. THIS COMBINED WITH SLIGHT UPSLOPING DUE
TO THE SE FLOW AHEAD OF THE FRONT MAKES THE HOOD CANAL THE ONLY
PLACE SNOW IS EXPECTED TO ACCUMULATE. A SNOW ADVISORY WILL BE ISSUED
FOR 1 TO 3 INCHES. OTHER LOCATIONS...ESPECIALLY THE LOWER CHEHALIS
VALLEY COULD SEE LOCALIZED ACCUMULATION OF AROUND AN INCH. SNOW
LEVELS WILL BE AROUND 500 FEET TONIGHT. THE FRONT WILL PUSH THROUGH
THE INTERIOR A LITTLE BEFORE 12Z...AND SHIFT THE FLOW TO SOUTHWEST.
ANY FROZEN PRECIP WILL TURN TO COLD RAIN SHOWERS AT THIS POINT. ONE
EXCEPTION COULD BE AS THE POST FRONTAL PRES RISES ALONG THE COAST
INDUCING A WEAK PSCZ WEDNESDAY IN THE NORTH/CENTRAL SOUND. HEAVIER
SHOWERS COULD BRIEFLY BRING THE SNOW LEVEL DOWN TO THE SURFACE.
OTHERWISE A TRANSIENT RIDGE WILL BUILD IN THE AFTERNOON WITH PARTIAL
CLEARING AND A GENERAL DECREASE IN SHOWER ACTIVITY.

STRONG FRONTAL SYSTEM ASSOCIATED WITH DEEP LOW PRES IN NE PACIFIC
APPROACHES WEDNESDAY NIGHT. PRECIP COULD AGAIN MIX WITH SNOW AT THE
ONSET...ESPECIALLY AROUND HOOD CANAL. THE FORECAST MODELS SEEM TO BE
COALESCING AROUND THE IDEA OF A COOLER SOLUTION. THE MAIN BAROCLINIC
BAND SLIDES SOUTH THROUGH THE AREA THURSDAY...STALLING OVER NE
OREGON. A SECONDARY WAVE DEVELOPS ALONG THE EXISTING BOUNDARY AND
LIFTS UP THE COASTLINE THURSDAY NIGHT TOWARD VANCOUVER ISLAND WITH A
FRONTAL PASSAGE ON FRIDAY. 500 MB HEIGHTS AND 850 MB TEMPS ARE MUCH
COOLER WITH THIS SETUP AS SNOW LEVELS ONLY RISE AS HIGH AS 3500
FEET. UNDER THIS SCENARIO...FOCUS HAS SHIFTED FROM FLOODING TO A
WINTER STORM WATCH FOR THE MOUNTAINS. THE PATTERN WILL FAVOR S-SW
FACING SLOPES AND THE VOLCANOES. LOCALLY WINDY S-SE WINDS WOULD
DEVELOP THURSDAY AND THURSDAY NIGHT WITH GUSTY SW WIND FRIDAY NIGHT
AS THE LOW PASSES NORTH AND EAST.

.LONG TERM...MODELS IN GOOD AGREEMENT IN POST FRONTAL ENVIRONMENT
FOR SATURDAY WITH SHOWERS SLOWLY DIMINISHING THROUGH THE DAY AS
SHORTWAVE RIDGING BUILDS IN THE AFTERNOON. WARM FRONTAL
PRECIPITATION FROM THE NEXT SYSTEM BEGINS TO BRUSH THE COAST SUNDAY
MORNING. ECMWF BUILDS THE RIDGE OVER E WA/MT STANDING UP THE FRONT
ON SUNDAY WHILE GFS PUSHES PRECIP FURTHER INLAND. FOR NOW HAVE
CONTINUED TO KEEP THE INTERIOR DRY. AS A DEEP TROUGH DEVELOPS OVER
THE NE PACIFIC...A SERIES OF SYSTEMS WILL LIFT NORTH OFF THE COASTAL
WATERS. THE PLACEMENT VARIES WITH MODEL CHOICE...BUT GENERAL PATTERN
WILL BE SOUTHWEST FLOW ALOFT WITH A BETTER CHANCE OF LIGHT RAIN
FURTHER WEST THROUGH EARLY NEXT WEEK. DAMICO

&&

.HYDROLOGY...SPLITTING FRONTAL SYSTEM WILL PUSH INLAND TONIGHT
DROPPING LIGHT AMOUNTS OF PRECIP MOSTLY IN THE FORM OF SNOW ACROSS
HIGHER TERRAIN. NEXT SYSTEM ASSOCIATED WITH A DEEPENING LOW PRES
SYSTEM IN THE NE PACIFIC WILL BRING A MORE CONSOLIDATED BOUT OF
PRECIPITATION BEGINNING WEDNESDAY NIGHT. STRONG S-SW FLOW OROGRAPHIC
ENHANCEMENT WILL HELP PRODUCE 2 INCHES OR MORE OVER 12 HOURS ON THE
SW SLOPES OF THE OLYMPICS AND CASCADES THROUGH THURSDAY AFTERNOON.
UNLIKE EARLIER FORECAST SOLUTIONS...THE FRONT WILL SAG SOUTH WITH
MORE COLD AIR REMAINING IN PLACE THROUGH FRIDAY. A SECONDARY WAVE
WILL DEVELOP ALONG THE BOUNDARY BRINGING MORE PRECIPITATION ON
FRIDAY. QPF AMOUNTS WILL RANGE TO NEAR 3 INCHES OVER THE OLYMPICS
AND 2-2.5 INCHES IN THE N.CASCADES. DUE TO THIS COLDER SOLUTION THE
GREATER THREAT WILL BE A WINTER STORM WATCH AND NOT FLOODING. AXIS
OF HEAVIEST PRECIPITATION WILL BE MONITORED FOR ANY CHANGES TOWARD A
WARMER SOLUTION. SHOWERY WEATHER WILL FOLLOW FRIDAY NIGHT AND
SATURDAY WITH A BREAK IN THE ACTION THROUGH EARLY SUNDAY. A DEEP
TROUGH WILL SET UP IN THE NE PACIFIC DIRECTING A SERIES OF SYSTEMS
IN MILDER SW FLOW TOWARD THE REGION. PLACEMENT AND TIMING OF HEAVIER
PRECIP IS VERY UNCERTAIN AT THIS TIME.

AT THIS TIME THE FLOOD THREAT IS LOW ALONG THE GREEN RIVER FOR THE
NEXT 10 DAYS. DAMICO


&&

.AVIATION...STRONG COLD FRONT MOVES THRU WRN WA TNGT. THE STRONGEST
AND WETTEST PART OF THE FRONT IS JUST OFF THE ORE COAST THIS
AFTERNOON AND THERE WONT BE A GREAT DEAL OF PRECIP ON TAP FOR WRN WA
OVERNIGHT...THIS SYSTEM IS ON THE COOLER DRIER SIDE. THE SNOW LEVEL
WILL PROBABLY AVERAGE 1000FEET OVER THE INLAND PORTION OF WRN WA...A
NOTCH LOWER AROUND HOOD CANAL. FRONTAL PASSAGE LOOKS TO BE ARND 8PM
ON THE SOUTH COAST...A LITTLE SLOWER IN THE NORTH...AND PROBABLY TO
THE I-5 CORRIDOR AROUND 2AM. SSW FLOW ALF INCREASING TONIGHT THEN A
SHIFT TO LIGHTER NW FLOW ALF WITH THE UPPER TROF PASSAGE WED
MORNING. THERE IS A GOOD CHANCE OF PSCZ ACTIVITY FROM KPAE NORTH WED
MORNING. THE NEXT WARMER AND WETTER SYSTEM IS ON TAP FOR THU. 19

KSEA...NO BIG CHANGES TO THE TAF EXPECTED...NOT A REAL WET FRONT SO
RAIN AT TIMES OVERNIGHT TURNING TO SHOWERS WITH THE FROPA ARND 10Z.
THERE IS A CHANCE OF SCATTERING OUT FOR AWHILE BY MIDDAY
WED...ALTHOUGH AREAS NORTH OF SEATTLE WILL PROBABLY BE DEALING WITH
A MORNING PSCZ. 19

&&

.MARINE...PREFRONTAL GALES COASTAL WATERS...AND WINDS SHOULD REACH
GALE FORCE NRN WATERS/ENTRANCES THIS EVENING. THERE IS A CHANCE THAT
THE WLY PUSH BEHIND THE FRONT GIVES SEVERAL HOURS OF WESTERLY GALES
IN THE CENTRAL STRAIT...THE 4KM WRFGFS MODEL SHOWS WINDS PEAKING AT
20-30KT ARND 3AM...WITH THE STRONGEST WIND AT DUNGENESS SPIT...THEN
DECREASING TO 15-25KT AT DAYBREAK. THERE WILL ONLY BE A SHORT 12
HOUR PAUSE WED BETWEEN THIS VIGOROUS COLD FRONT TONIGHT AND THE NEXT
FRONTAL SYSTEM WITH SLY GALES DEVELOPING AGAIN COASTAL WATERS WED
EVENING...SPREADING TO THE NORTHERN INLAND WATERS BY DAYBREAK THU. I
HAVE NOT CHANGED THE FCST BUT THAT 4KM MODEL SHOWS WINDS DECREASING
BEHIND THE FRONT FOR THE COASTAL WATERS THU MORNING...WHILE KEEPING
A FULL GALE GOING TIL MIDDAY IN THE NRN WATERS. IT MIGHT PAY OFF TO
SEE ANOTHER RUN OF THE MODELS BEFORE PROMISING A FROPA THU MORNING
IT SEEMS EQUALLY LIKELY THE FRONTAL SYS WILL STALL OVER WRN WA AND
THE SLY GALES COULD PERSIST THRU THE WHOLE DAY. 19

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WINTER WEATHER ADVISORY HOOD CANAL.
PZ...GALE WARNING COASTAL WATERS AND WEST AND EAST ENTRANCE JUAN DE
     FUCA...NORTHERN INLAND WATERS.
     SMALL CRAFT ADVISORY CENTRAL STRAIT AND ADMIRALTY INLET.
     SMALL CRAFT ADVISORY FOR ROUGH BAR GRAYS HARBOR BAR.

$$

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NWS SEW Office Area Forecast Discussion