Flood Potential Outlook
Issued by NWS Blacksburg, VA

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Winter/Spring Flood Potential Outlook
National Weather Service Blacksburg VA
318 PM EDT Thu Mar 15 2018

...Winter/Spring Flood Outlook...Number 6

...River flood potential below normal...

Each winter and early spring, the National Weather Service office
in Blacksburg issues a series of routine flood potential
outlooks. These outlooks estimate the potential for river
flooding (not flash flooding) across the Blacksburg office`s
Hydrologic Service Area (HSA). The HSA includes 40 counties
covering parts of southwest Virginia, far northwest North
Carolina and far southeast West Virginia. Major river basins in
the HSA include all or parts of the New, Greenbrier, Tennessee,
James, Roanoke, Dan, and Yadkin. This outlook is based on the
current assessment of hydrometeorological factors which contribute
to river flooding. These factors include, but are not limited to,
recent precipitation, soil moisture, snow cover and snow water
equivalent, stream flows, river ice and expected future weather
conditions.

In this part of the southern Appalachian and Mid-Atlantic region,
heavy rainfall is the primary factor that leads to river
flooding. Heavy rainfall can rapidly cause river flooding at any
time of the year, even when overall river flood potential is
considered low.

Flood Potential Outlook:
For the Blacksburg HSA, the river flood potential is below normal
for the next two weeks (through March 29th) based on antecedent
conditions and current forecasts. Most of the area is actually
quite dry and drought is a bigger concern than flooding.

Current Flooding:
There is no flooding occurring or forecast at this time.

Recent Precipitation:
March has been generally drier than normal through mid-month,
with precipitation amounts ranging from as low as 0.50 inches in
parts of the James River basin to nearly 3 inches in the far
western mountains and far southeast piedmont. As a percent of
normal the amounts range from less than 50 percent up to around
100 percent for this period. Temperatures have been mostly below
normal after a record to near-record warm February which has
slowed a very early onset of the spring greenup.

February precipitation was above normal in all areas except for
the far eastern piedmont and was well above normal in the far
west, including most of the Tennessee and Greenbrier basins. Mean
precipitation was 4.84 inches versus the 30-year (1981-2010)
average of 3.84 or 126 percent of normal. Single station values
ranged from 2.07 inches at Keysville in Charlotte County, VA to a
a maximum of 7.63 inches at Richlands in Tazewell County, VA.

The mean precipitation for January was 2.42 inches or 73 percent
of the 30-year normal of 3.32 inches.

Both November and December 2017 were exceptionally dry for the
entire HSA. The combined HSA-wide precipitation was 2.27 inches
which was only 28 percent of the normal 7.74 inches for that
period. At numerous sites it was the driest or second driest such
period on record.

Drought:
Abnormally dry conditions (D0 on the U.S. Drought Monitor)
remains in place across parts of the Blue Ridge and foothills into
the western piedmont in VA and NC. A persistent area of Moderate
Drought (D1 conditions) remains in place across the lower reaches
of the Staunton and Dan River basins which has persisted most of
the winter.

Please visit the www.droughtmonitor.unl.edu/ for access to the
drought maps and additional information.

Snow cover:
Most areas have lost the snow cover from the March 11-12 event and
only the higher mountains have significant amounts.

Please visit www.nohrsc.noaa.gov for detailed information on snow
cover and snow water equivalent.

River ice:
There is no river ice anywhere in the HSA at this time.

Streamflow:
USGS real-time streamflows at durations from daily out to 14-day
averages are all showing below normal flows, while the 28-day
flows are still near normal in the western HSA below normal in
the central and eastern HSA.

For more detailed information on streamflow conditions see the
USGS WaterWatch website:
https://waterwatch.usgs.gov

Soil Moisture:
Soil moisture analyses from the Climate Prediction Center (CPC)
indicate continued moisture deficits across the Blue Ridge
foothills and the piedmont of northern North Carolina into central
Virginia. These deficits range from 1" to 2.5" below normal soil
moisture values. Deficits decrease to near zero further west
across the mountains.

For additional soil moisture information see:
http://www.cpc.ncep.noaa.gov

Reservoirs:
Major water supply reservoirs including John H. Kerr, W. Kerr
Scott, Philpott Lake, Lake Moomaw and Smith Mountain Lake are near
guide curves where applicable.

Future Weather Conditions:
Quantitative precipitation forecasts (QPF) from the Weather
Prediction Center (WPC) over the next 7 days (through 7 AM
Thursday, March 22nd) show amounts of about 0.50 to 1.00 inches
across nearly all of the HSA, Overall, these amounts are slightly
below normal and do not present a significant flood threat.

WPC QPF is updated frequently and is available at:
www.wpc.ncep.noaa.gov/#page=qpf

The longer term outlooks for the 6 to 10 and 8 to 14 day periods
through March 28th show an enhanced likelihood of below normal
temperatures across the entire HSA. Precipitation chances above
normal.

For additional long range forecast information see:
http://www.cpc.ncep.noaa.gov

Probabilistic/Ensemble river forecasts:
The Meteorological Model Ensemble River Forecasts (MMEFS) valid
through about March 22nd indicate little to no potential for
river flooding through the period.

Ensemble river forecasts (MMEFS) are available at:
www.weather.gov/erh/mmefs

Summary:
The river flood potential is below normal through the outlook
period, based on current conditions and forecasts.

Next issuance:
This is the final scheduled winter/spring flood potential outlook
for 2018. Another may be issued if conditions warrant.

For additional hydrologic or weather information, visit our
website at weather.gov/blacksburg.


$$

PC



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