Flood Potential Outlook
Issued by NWS Blacksburg, VA

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NCZ001>006-018>020-VAZ007-009>020-022>024-032>035-043>047-058-059-WVZ
042>045-191800-

WINTER/SPRING FLOOD POTENTIAL OUTLOOK
NATIONAL WEATHER SERVICE BLACKSBURG VA
1220 AM EST SAT FEB 6 2010

...WINTER/SPRING FLOOD OUTLOOK...NUMBER 3

...EXTENSIVE SNOW COVER MAINTAINS ABOVE NORMAL FLOOD POTENTIAL
ACROSS THE AREA...

THIS IS THE THIRD IN A SERIES OF ANNUAL WINTER/SPRING FLOOD
POTENTIAL STATEMENTS INTENDED TO PROVIDE INSIGHT INTO THE LIKELIHOOD
OF RIVER FLOODING (NOT FLASH FLOODING) ACROSS THE BLACKSBURG
HYDROLOGIC SERVICE AREA (HSA). THIS INCLUDES ALL OR PARTS OF THE
JAMES ...ROANOKE...UPPER YADKIN...GREENBRIER...NEW...CLINCH AND
HOLSTON RIVER BASINS IN WESTERN VIRGINIA...SOUTHEAST WEST VIRGINIA
AND NORTHWEST NORTH CAROLINA.

THESE STATEMENTS PROVIDE INFORMATION ON FLOOD THREAT CONDITIONS
SUCH AS RECENT PRECIPITATION...SOIL MOISTURE...SNOW COVER AND ITS
WATER EQUIVALENT...RIVER ICE CONDITIONS...STREAMFLOW...FUTURE
PRECIPITATION AND OTHERS FACTORS. THIS OUTLOOK IS VALID FOR THE
PERIOD THROUGH FEBRUARY 19 2010.

FOR THE BLACKSBURG HSA THE POTENTIAL FOR FLOODING DURING THE OUTLOOK
PERIOD IS ABOVE AVERAGE BASED PRIMARILY ON SIGNIFICANT SNOW
COVER...WET SOIL CONDITIONS...AND HIGH CURRENT STREAMFLOWS. FLOOD
WARNINGS ARE VERY POSSIBLE IN THE NEXT FEW DAYS ON PORTIONS OF THE
DAN RIVER AND POSSIBLY LOWER ROANOKE RIVERS AS SNOWMELT AND RUNOFF
FROM THE CURRENT RAIN IN THOSE AREAS FILLS THE RIVERS.

IN THIS PART OF THE MID-ATLANTIC REGION HOWEVER...IT IS HEAVY
RAINFALL THAT IS THE PRIMARY FACTOR LEADING TO RIVER FLOODING. IT IS
IMPORTANT TO NOTE THAT HEAVY RAINFALL CAN RAPIDLY CAUSE RIVER
FLOODING ANY TIME OF THE YEAR...EVEN WHEN OVERALL RIVER FLOOD
POTENTIAL IS CONSIDERED LOW OR BELOW AVERAGE.

IT SHOULD BE POINTED OUT THAT NO MAJOR WARM RAIN EVENTS ARE
CURRENTLY ANTICIPATED WHICH COULD CAUSE A RAPID MELT OF THIS
SNOWPACK... SIMILAR TO WHAT OCCURRED IN JANUARY 1996 ACROSS THIS
REGION AND LED TO MAJOR FLOODING ON SOME RIVERS.

CURRENT FLOODING...

SOME FLOODING WAS REPORTED IN TAZEWELL COUNTY VIRGINIA THIS EVENING
AS RAIN AND SNOWMELT COMBINED TO CAUSE THE CLINCH RIVER TO COME OUT
OF ITS BANKS. THE DAN RIVER IS ALREADY RUNNING VERY HIGH AND FLOOD
FORECASTS ARE POSSIBLE IN THE NEXT DAY OR SO.

RECENT PRECIPITATION...

JANUARY WAS SOMEWHAT WETTER THAN NORMAL WITH AN AVERAGE OF 4.84
INCHES OF PRECIPITATION AT 54 OF THE 75 NWS COOPERATIVE STATIONS
WITH COMPLETE DATA. JANUARY MEAN PRECIPITATION (1971-2000
CLIMATOLOGICAL NORMALS) IS 3.65 INCHES SO THE MONTH WAS 133 PERCENT
OF THE LONG-TERM AVERAGE. THIS FOLLOWS AN EXTREMELY WET NOVEMBER AND
DECEMBER. THE 3-MONTH PERIOD FROM NOVEMBER 1 THROUGH JANUARY 31 HAS
BEEN EXTRAORDINARILY WET ACROSS MOST OF THE HSA. THIS WAS THE
WETTEST COMBINED PERIOD DURING THE CLIMATE PERIOD OF RECORD FOR
SEVERAL OF THE OFFICIAL CLIMATE OBSERVING SITES...INCLUDING
LYNCHBURG (19.80 INCHES - OLD RECORD 16.88 IN 1935)...ROANOKE (20.27
INCHES - 17.81 IN 1948)...BLACKSBURG (15.69 INCHES - 13.69 IN 1972)
AND DANVILLE (17.60 INCHES - 16.88 IN 1948). CLIMATE RECORDS GO BACK
TO 1893 AT LYNCHBURG...1912 AT ROANOKE...1952 AT BLACKSBURG AND 1948
AT DANVILLE.

SNOW COVER...

SNOW COVER WAS REESTABLISHED WITH LAST WEEKENDS STORM...JANUARY
28-29 WHICH DROPPED FROM 6 TO 12 INCHES ACROSS THE ENTIRE HSA.
MIDWEEK MOUNTAINS SNOW ADDED SEVERAL INCHES TO THE TOTALS IN THOSE
AREAS WHILE SUBSTANTIAL MELTING TOOK PLACE IN THE PIEDMONT. THE
CURRENT MAJOR STORM IS ADDING TO THE AMOUNTS ON THE GROUND. SNOW
DEPTHS FROM THE STORM HAVE RANGED FROM 3 TO 10 INCHES BUT THERE HAS
BEEN CONSIDERABLE SLEET AND FREEZING RAIN AND EVEN SOME RAIN. HENCE
SNOW WATER EQUIVALENTS WHEN ALL IS SAID AND DONE MAY RANGE FROM AN
ADDITIONAL 1 TO 2 INCHES. ADDED TO THE EXTANT SNOWPACK AND THE WATER
SITTING ON THE GROUND RANGES GENERALLY FROM FROM 1 TO 3
INCHES...WITH SOME POCKETS OF LOWER AND HIGHER VALUES. THIS
REPRESENTS A SIGNIFICANT POTENTLY FOR FLOODING BUT IT WILL TAKE A
RAPID WARM-UP OR WARM RAINFALL TO UNLOCK THAT POTENTIAL.

RIVER ICE...

THERE MAY BE SOME RIVER ICE ALTHOUGH THE AMOUNT IS NOT AS
SUBSTANTIAL AS MID-JANUARY WHEN SEVERAL ICE JAMS OCCURRED ON THE NEW
RIVER.

STREAMFLOW...

STREAMFLOWS ACROSS THE AREA ARE ALREADY VERY HIGH...MANY RUNNING
ABOVE THE  90TH PERCENTILE OF ALL FLOWS FOR THIS DATE. THE DAN RIVER
IS ALREADY APPROACHING BANKFULL STAGE IN ITS LOWER REACHES TOWARD
SOUTH BOSTON AND FLOWS IN THE CLINCH BASIN ARE ALSO VERY HIGH WHERE
RAIN FELL TODAY INSTEAD OF SNOW. FOR MORE DETAILED INFORMATION ON
STREAMFLOW CONDITIONS SEE THE USGS WATERWATCH SITE BELOW.

HTTP://WATERDATA.USGS.GOV/WATERWATCH

SOIL MOISTURE...

THE PALMER DROUGHT SEVERITY INDEX...USEFUL AS SOIL MOISTURE
INDICATOR... FOR JANUARY 30 2009 SHOWS WET OR EXCESSIVELY WET SOIL
CONDITIONS IN ALL THE CLIMATE ZONES WITHIN THE BLACKSBURG HSA.

FUTURE WEATHER CONDITIONS...

ONCE THE CURRENT STORM EXITS IT WILL BE DRY FOR SEVERAL DAYS
ALTHOUGH A MID-WEEK SYSTEM COULD BRING MODERATE PRECIPITATION
POSSIBLY AN ADDITIONAL 0.25 TO 0.75 INCHES OF LIQUID
EQUIVALENT...RAIN OR SNOW.

TEMPERATURES WILL HAVE A BIG IMPACT IN THE FLOOD OUTLOOK.
FORTUNATELY IT IS ALSO EXPECTED TO BE COLD FOR THE NEXT 5 TO 7 DAYS
WHICH WILL ALLOW ONLY SLIGHT MELTING OF THE SNOWPACK. FROM THE BLUE
RIDGE FOOTHILLS WEST THROUGH THE MOUNTAINS DAYTIME HIGHS THIS WEEK
WILL STRUGGLE TO REACH THE LOW OR MID-30S THUS LIMITING THE MELTING
IN THOSE AREAS. EVEN ACROSS THE PIEDMONT HIGHS ARE FORECAST TO REACH
THE LOW 40S WHICH WILL ALLOW SOME MELTING ALTHOUGH NOT A RAPID
MELT...ALTHOUGH THERE IS LESS SNOW ACROSS THESE AREAS ANYWAY.

IN ADDITION...THE LONGER RANGE WEATHER FORECASTS DO NOT SUGGEST A
RAPID MELT OF THE SNOW WHERE IT CURRENTLY EXISTS. FOR THE 6 TO 10
PERIOD FROM FEBRUARY 11 THROUGH FEBRUARY 15 BELOW NORMAL
TEMPERATURES AND NEAR NORMAL PRECIPITATION IS FORECAST. A SIMILAR
FORECAST EXISTS IN THE 8 TO 14 DAY OUTLOOK PERIOD...FEBRUARY 13
THROUGH FEBRUARY 19...COLD WITH NEAR OR SLIGHTLY BELOW NORMAL
PRECIPITATION.

PLEASE SEE THE CPC WEBSITE FOR ADDITIONAL FORECAST
DETAILS: HTTP://WWW.CPC.NCEP.NOAA.GOV

REPEATING THE CURRENT FLOOD POTENTIAL FOR THE BLACKSBURG HYDROLOGIC
SERVICE AREA...ABOVE NORMAL.

THIS OUTLOOK WILL BE UPDATED ON OR AROUND FEBRUARY 19 2010.

$$

PC