Debris Flow and Flood in Washington, November 16 to 17, 2009

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
915 PM PST SUN NOV 15 2009

.SYNOPSIS...A VIGOROUS STORM SYSTEM WILL MOVE ACROSS WESTERN
WASHINGTON TONIGHT...AND ANOTHER ONE WILL AFFECT THE AREA TUESDAY
NIGHT. HEAVY RAIN WILL FALL IN THE OLYMPICS AND NORTH CASCADES. HIGH
WINDS WILL ALSO AFFECT PARTS OF WESTERN WASHINGTON AT TIMES. ANOTHER
STRONG FRONTAL SYSTEM WILL ARRIVE WEDNESDAY NIGHT OR THURSDAY. THE
WEATHER PATTERN WILL REMAIN ACTIVE INTO NEXT WEEKEND.

&&

.SHORT TERM...MAIN FOCI TONIGHT ARE RAIN AND WIND. RAIN IS DEALT
WITH IN THE HYDROLOGY SECTION BELOW. AS FOR WIND...THE HIGH WIND
WARNING FOR THE COAST AND NORTH INTERIOR FOR TONIGHT WILL REMAIN IN
EFFECT. THERE IS LIKELY TO BE MARGINAL HIGH WIND IN BOTH PLACES AT
TIMES TONIGHT. THEN ON MONDAY THERE WILL BE A SIGNIFICANT LULL IN
THE WIND AS ONE LOW DRIFTS FAR TO THE NORTH AND ANOTHER ONE SPINS UP
FAR TO THE SOUTHWEST.

THE SECOND LOW WILL ALSO BRING WIND TO THE COAST AND NORTH INTERIOR.
THE STRENGTH OF THE WIND IS IN SOME DOUBT AND THE WARNING CURRENTLY
IN EFFECT FOR MONDAY NIGHT WILL BE CHANGED TO A HIGH WIND WATCH FOR
THIS EVENT. ON TUESDAY A COLD FRONT WILL SWEEP THROUGH THE AREA.
OVER THE SEATTLE METRO AREA STRONG WINDS ARE LIKELIEST DURING THE
POST FRONTAL SURGE. THE GOOD NEWS IS THAT THE COLD FRONT WILL BRING
COLDER AIR TO THE MOUNTAINS...CHANGING RAIN TO SNOW...AND ENDING ANY
HYDROLOGICALLY SIGNIFICANT PRECIPITATION.

TEMPERATURES TOPPED OUT AROUND 50 THIS AFTERNOON AND ARE LIKELY TO
REMAIN NEAR THAT VALUE THROUGH THE NIGHT. ON MONDAY HIGHS WILL BE
FIVE DEGREES OR SO HIGHER. ON TUESDAY HIGHS WILL DROP BACK INTO THE
40S AND STAY THERE WEDNESDAY. BURKE

.LONG TERM...PREVIOUS DISCUSSION...THE NEXT STRONG SYSTEM WILL
AFFECT WESTERN WASHINGTON WEDNESDAY NIGHT THROUGH THURSDAY. MODELS
SHOW THIS SYSTEM TO BE MORE PROGRESSIVE THAN THE ONE CURRENTLY
AFFECTING THE AREA. THIS WILL HELP LIMIT QPF AMOUNTS BUT RAIN AND
LOCALLY WINDY CONDITIONS WILLS STILL DEVELOP ACROSS THE AREA. THE
PATTERN BECOMES MORE UNCERTAIN BEHIND THE FRONT FRIDAY INTO THE
WEEKEND. BUT MODELS GENERALLY SHOW A COOL AND SHOWERY PATTERN INTO
THE WEEKEND.

&&

.HYDROLOGY...LOOKED AT THE LAST TWO RUNS OF EACH OF FOUR DIFFERENT
MESOSCALE MODELS...MM5-ETA-12KM...MM5-GFS-12KM...MM5-GFS-4KM...AND
NAM-12KM. THE AVERAGE OF THESE 8 RUNS HAS MAXIMA OF 9 INCHES OVER
THE OLYMPICS AND 7 INCHES OVER THE FAR NORTH CASCADES DURING THE
36-HOUR PERIOD 00Z MONDAY THROUGH 12Z TUESDAY. LOADED THE MODEL
CLOSEST TO THE AVERAGE INTO THE GRIDS AND MODIFIED THEM A BIT.

WITHIN THIS TIME THERE IS A BIG SLUG OF RAIN OVER THE OLYMPICS AND
NORTH CASCADES IN THE FIRST 18 OR SO HOURS...THEN A LULL IN THE
PRECIPITATION MONDAY AFTERNOON...THEN ANOTHER SLUG AS THE DEVELOPING
WAVE OFFSHORE BRINGS THE FRONT BACK NORTH AGAIN FOR SIX TO TWELVE
MORE HOURS. THERE IS A PERIOD MONDAY EVENING WHEN THERE IS PRETTY
DECENT RAINFALL IN THE SEATTLE METRO AREA AS WELL AS THE MOUNTAINS.
EARLIER CONCERNS ABOUT MINOR URBAN FLOODING APPLY MAINLY TO THIS
PERIOD.

NOW FOR THE RIVERS...OF MOST CONCERN IS THE SKOKOMISH AND THE
WARNING WENT OUT EARLIER THIS EVENING FOR FLOODING MONDAY. TWO TO
THREE INCHES OF RAIN HAS ALREADY FALLEN IN THE OLYMPICS. IT WOULD
SEEM THAT WITH 9 INCHES OF RAIN IN THE OLYMPICS THE FLOODING COULD
BE MAJOR...BUT RIVER MODELS STUBBORNLY KEEPS THE SKOKOMISH BELOW
MAJOR FLOOD STAGE. FORECAST IS FOR A CREST JUST BELOW MAJOR FLOOD
STAGE...BUT THIS NEEDS TO BE WATCHED CAREFULLY.

THE REST OF THE RIVERS ON THE OLYMPIC PENINSULA SEEM RIPE FOR
FLOODING IF THE RAIN KEEPS UP. RIVERS IN THE NORTHWEST CORNER HAVE
ALREADY RISEN SHARPLY THOUGH THEY ARE NOT CLOSE TO FLOOD STAGE YET.
THE LULL IN PRECIPITATION MONDAY AFTERNOON MAY PREVENT A WIDESPREAD
MAJOR FLOOD EVENT...BUT IT DOES SEEM LIKELY THAT MORE RIVERS THAN
JUST THE SKOKOMISH WILL FLOOD AND THE FLOOD WATCH REMAINS IN EFFECT.

THE NOOKSACK RIVER IN WHATCOM COUNTY IS ALSO FORECAST TO RESPOND
SHARPLY TO THE RAIN. SOME UPSTREAM GAUGES SHOW STRONG RISES BUT
NOTHING IS NEAR FLOOD STAGE YET. THE SAUK RIVER IN THE UPPER SKAGIT
BASIN IS RISING FAST...BUT THE SKAGIT IS A BIG RIVER AND THE
FORECAST IS STILL FOR NO FLOODING THERE. EARLIER TODAY NEARLY THREE
INCHES OF RAIN FELL IN THE STILLAGUAMISH BASIN. THE RIVER ROSE BUT
THE FORKS NOW SEEM TO BE CRESTING WELL BELOW FLOOD STAGE. MORE RAIN
IS FORECAST OF COURSE AND ALL THREE BASINS REMAIN UNDER A FLOOD
WATCH.

RIVERS IN THE CENTRAL CASCADES WILL SEE RISES BUT THE FOCUS OF
PRECIPITATION IS ELSEWHERE. NO FLOODING IS EXPECTED ON THE GREEN
RIVER.

IT SHOULD BE NOTED THAT FORECASTS CALL FOR A PERIOD OF HEAVY RAIN IN
THE WILLAPA HILLS IN THE SECOND ROUND OF RAIN ON MONDAY NIGHT. THIS
COULD CAUSE LOCAL PROBLEMS AND THE CHEHALIS RIVER WILL RISE
SIGNIFICANTLY. LATER TONIGHT THIS AREA MAY HAVE TO BE ADDED TO THE
WATCHED ZONES.

THE WEATHER WILL REMAIN WET AT TIMES INTO NEXT WEEK...BUT NO SYSTEM
CURRENTLY LOOKS LIKE A FLOOD PRODUCER. MODELS GENERALLY SHOW A COOL
AND SHOWERY PATTERN INTO THE WEEKEND. BURKE

&&

.AVIATION...STRONG SOUTHWEST FLOW CONTINUES ALOFT OVER WESTERN
WASHINGTON WITH A WARM FRONT OVER SOUTHWEST BRITISH COLUMBIA AND A
COLD FRONT EXTENDING SOUTHWEST FROM VANCOUVER ISLAND ACROSS THE
WASHINGTON OFFSHORE WATERS. STRONG SOUTHEAST PRESSURE GRADIENTS WILL
CONTINUE AT THE SURFACE THROUGH MONDAY AS THE COLD FRONT MOVES
SLOWLY EAST. THE AIR MASS WILL REMAIN MOIST AND STABLE.

CEILINGS ACROSS WESTERN WASHINGTON WILL REMAIN MOSTLY IN THE
2000-4000 FT RANGE TONIGHT AND MONDAY MORNING. LOWER CONDITIONS WILL
CONTINUE ALONG THE COAST WHERE RAIN IS HEAVIER AND STEADIER...AND
LOWER CONDITIONS WILL OCCASIONALLY OCCUR IN THE INTERIOR DURING
PERIODS OF HEAVIER RAIN TONIGHT. PRECIPITATION WILL INCREASE ACROSS
THE FORECAST AREA LATE MONDAY MORNING AND MONDAY AFTERNOON...AND
CONDITIONS WILL DETERIORATE TO A MIX OF MVFR AND IFR AT THAT TIME.

STRONG LOW LEVEL WINDS WILL CONTINUE TONIGHT AND MONDAY. OUR LOCAL
PROFILER WAS INDICATING 50 KT SOUTHERLY WINDS AT 3000 FT...AND THIS
WILL LIKELY RISE TO AROUND 60 KT MONDAY MORNING.

KSEA...SOUTHERLY WIND 8-16 KT TONIGHT THROUGH MIDDAY MONDAY. SOUTH
WIND WILL RISE TO 15 TO 25 KT GUSTING 35 KT MONDAY NIGHT. MCDONNAL

&&

.MARINE...A VIGOROUS FRONTAL SYSTEM WILL CONTINUE TO AFFECT THE
FORECAST AREA THROUGH TUESDAY. A WARM FRONT IS CURRENTLY OVER
SOUTHWEST BRITISH COLUMBIA...WITH A STRONG COLD FRONT EXTENDING
SOUTHWEST FROM VANCOUVER ISLAND ACROSS THE OFFSHORE WATERS. THIS
FEATURE WILL PRODUCE STORM FORCE WINDS OVER THE COASTAL
WATERS...ENTRANCES TO THE STRAIT OF JUAN DE FUCA...AND NORTHERN
INLAND WATERS TONIGHT AND MONDAY MORNING. GALE WARNINGS ARE IN
EFFECT FOR THE REMAINING WATERS EXCEPT THE CENTRAL STRAIT.

AFTER A BRIEF RELATIVE LULL IN THE ACTION...A DEVELOPING 980 MB LOW
WILL MOVE NORTHEAST ACROSS THE OFFSHORE WATERS MONDAY NIGHT AND
CROSS VANCOUVER ISLAND TUESDAY MORNING. THE LOW COULD PRODUCE
ANOTHER ROUND OF STORM FORCE WINDS OVER THE SAME AREAS...WITH GALES
LIKELY ELSEWHERE. MOVING THROUGH THE OFFSHORE WATERS AND INTO
VANCOUVER ISLAND MONDAY WILL GIVE A BURST OF STORM FORCE WINDS TO
THE COASTAL WATERS...ENTRANCES...AND NORTHERN INLAND WATERS. GALES
WILL DEVELOP ELSEWHERE.

I HAVE SHORTENED THE STORM WARNING TO GO THROUGH MONDAY WARNING...
AND POSTED A STORM WATCH FOR THE SECOND EVENT MONDAY NIGHT THROUGH
TUESDAY MORNING.

COASTAL FLOODING...WHILE NOT CERTAIN...IS A POSSIBILITY WITH THE
HIGH TIDE THAT OCCURS MIDDAY TUESDAY. LOW PRESSURE...PERSISTENT
STRONG SOUTH WIND ALONG THE COAST...AND HIGH WAVES OF 20 FT...COULD
GIVE TIDAL ANOMALIES OF 2 TO 3 FT....AND THIS COULD CAUSE SOME
FLOODING IF THE STORM TIMING LINES UP WITH THE MIDDAY TUESDAY HIGH
TIDE. A COASTAL FLOOD WATCH HAS BEEN ISSUED FOR TUESDAY ALONG THE
CENTRAL COAST.

ANOTHER VIGOROUS FRONT WILL MOVE THROUGH THE AREA WEDNESDAY NIGHT OR
EARLY THURSDAY. MCDONNAL

&&

.AVALANCHE...RELATIVELY LARGE AMOUNTS OF RECENT COLD..WEAK SNOW
LAYERS ARE GRADUALLY BEING EITHER LOADED OR WEAKENED BY INCREASINGLY
HEAVY ...DENSER SNOW OR RAIN WITH INCREASED AVALANCHE ACTIVITY THE
LIKELY OUTCOME. THIS WEATHER TREND OF WARMER...WET...AND WINDY
SHOULD CONTINUE RELATIVELY UNABATED OVER THE NEXT 24 HOURS IN THE
OLYMPICS AND NORTHERN WA CASCADES...THOUGH A BRIEF DECREASE IN
PRECIPITATION INTENSITY IS LIKELY IN THE SOUTH AND CENTRAL CASCADES
OVERNIGHT. AS A RESULT OF BOTH CURRENT AND ANTICIPATED WEATHER A
SIGNIFICANT INCREASE IN THE AVALANCHE DANGER IS UNDERWAY WITH
APPROPRIATE WARNINGS ISSUED FOR GENERALLY HIGH DANGER IN THE NORTH
CASCADES AND OLYMPICS AND MORE MODEST THOUGH STILL SIGNIFICANT
DANGER INCREASES ELSEWHERE. DESPITE THE BRIEF DECREASE IN THE SOUTH
AND CENTRAL CASCADES OVERNIGHT...FURTHER STRONG STORM RELATED
PRECIPITATION AND VERY STRONG WINDS SHOULD RETURN LATER MONDAY INTO
EARLY TUESDAY. EARLY SEASON BACK COUNTRY TRAVELERS SHOULD MINIMIZE
THEIR TIME IN AND EXPOSURE TO STEEPER AVALANCHE TERRAIN UNTIL THE
RECENT SNOWPACK BEGINS TO STABILIZE ...EITHER THROUGH SETTLEMENT OR
FURTHER AVALANCHES. SEE NWAC.US FOR DETAILS. MOORE

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...HIGH WIND WARNING COAST AND NORTH INTERIOR THROUGH NOON MONDAY.
     HIGH WIND WATCH FOR ALL ZONES EXCEPT CENTRAL CASCADES FOR
     MONDAY EVENING THROUGH TUESDAY AFTERNOON.
     FLOOD WATCHES AND WARNINGS ARE IN EFFECT FOR VARIOUS COUNTIES.
     COASTAL FLOOD WATCH FOR CENTRAL COAST TUESDAY.
PZ...STORM WARNING TONIGHT AND MONDAY MORNING COAST...ENTRANCES...
     AND NORTH INLAND WATERS.
    .GALE WARNING ADMIRALTY INLET...PUGET SOUND AND HOOD CANAL.
    .SMALL CRAFT ADVISORY GRAYS HARBOR FOR ROUGH TO SEVERE BAR
      CONDITIONS.
    .STORM WATCH MONDAY NIGHT AND TUESDAY COASTAL WATERS...STRAIT OF
     JUAN DE FUCA...NORTHERN INLAND WATERS.
    .SMALL CRAFT ADVISORY CENTRAL STRAIT.

WWW.WEATHER.GOV/SEATTLE

FOR AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION...PLEASE SEE
WWW.WEATHER.GOV/SEATTLE/GAFD/LATESTWEBAFD.HTML.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SEATTLE WA
901 PM PST SUN NOV 15 2009

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

0900 PM     NON-TSTM WND GST 2 WNW ANACORTES         48.50N 122.66W
11/15/2009  M49 MPH          SKAGIT             WA   TRAINED SPOTTER

&&