Flood Potential Outlook
Issued by NWS Blacksburg, VA

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Winter/Spring Flood Potential Outlook
National Weather Service Blacksburg VA
118 PM EDT Thu Mar 21 2019

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

...River flood potential is near 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 near normal through the period. Wet soil conditions
remain in place across the HSA, however stream flows have trended
closer to normal for this time of year due to drier conditions
thus far for March. In addition, expected rainfall amounts in the
foreseeable future do not appear sufficient to cause more than
minor and localized flooding issues, if any.

Current Flooding: There are no rivers in flood anywhere in the
HSA at this time.

Recent Precipitation: Nearly all of the precipitation during the
month of March fell as rain. Amounts vary from 1.50 to 2.00 inches
for the mountains and foothills south of the Interstate 64
corridor, anywhere from 50 to 90 percent of the long-term
averages. Elsewhere, 2.00 to 3.00 inches were observed along and
north of the I-64 corridor, as well as across much of the
Piedmont. Locally higher amounts have occurred at a few locations.
These amounts are near to slightly above normal for March.

February was a wet month for the HSA as precipitation ranged
generally from 5 to 7 inches for most of the area, with over 7
inches observed across portions of far western Virginia. The mean
precipitation amount was 5.93 inches, roughly 150 to 200 percent
of the long-term averages across the entire HSA.

January precipitation was slightly above average with a mean of
3.73 inches versus the long-term (1981-2010) normal mean of 3.32
inches or 112 percent of normal.

Conditions were very wet from October through December 2018 with
precipitation roughly 150 to 200 percent of the long-term averages
across the entire HSA.

Drought: There is no drought anywhere in the HSA at this time and
none is expected to develop during the outlook period.

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

Snow cover: There is no snow cover anywhere in the HSA at this
time.

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: Given drier conditions during the month of March,
USGS real-time streamflows at 7-day and 14-day averages are
running near to slightly above normal. 28-day averages remain much
above normal across the 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 surpluses ranging from
3.0 to 4.0 inches above normal across the entire HSA.

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 the Roanoke
area reservoirs of Carvins Cove and Spring Hollow, are near or
above average or 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 28th) indicate potential for
precipitation amounts ranging from about 0.75 to 1.50 inches
across most of the HSA, with locally higher amounts possible along
the west-facing ridges across the mountains. This includes up to
an additional 0.50 inches of rain expected to fall across the
Piedmont after 11:00 a.m. on March 21st. Much of the remainder of
expected precipitation will fall during the passage of another low
pressure system during March 26th-27th.

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

The longer term outlook for the 6 to 10-day period through March
30th indicate an increased chance for below-normal temperatures,
which then trend to around normal for the 8 to 14-day period
ending April 3rd. Precipitation through both of the above-
mentioned periods is expected to remain above slightly normal
across the HSA.

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 28th
indicate a low potential for flooding along any rivers within the
HSA.

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

Summary: For the Blacksburg HSA, the river flood potential is
near normal through the period. Wet soil conditions remain in
place across the HSA, however stream flows have trended closer to
normal for this time of year due to drier conditions thus far for
March. In addition, expected rainfall amounts in the foreseeable
future do not appear sufficient to cause more than minor and
localized flooding issues, if any.

Next issuance: This will be the final regular issuance for the
winter/spring 2019 season. This outlook may be updated if
conditions warrant.

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

$$


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