Flood Potential Outlook
Issued by NWS Blacksburg, VA

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Winter/Spring Flood Potential Outlook
National Weather Service Blacksburg VA
202 PM EST Mon Jan 9 2017

...Winter/Spring Flood Outlook...Number 1

...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 parts of southwest Virginia,
northwest North Carolina and southeast West Virginia. The 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:
In the Blacksburg HSA the river flood potential is below normal
for the outlook period from today through January 19th.

Current Flooding:
There is no flooding at this time.

Recent Precipitation:
The first week of January has seen precipitation from rain and
snow ranging from nearly 2 inches of liquid in the far southeast
to around 1 inch across most of the HSA. December precipitation
was close to average overall with a mean of 3.28 inches at the
network of 58 COOP and ASOS sites versus the long term (1981-2010)
normal of 3.32 inches or 99 percent of normal. There was a
considerable range however, with amounts ranging from around 1.50
inches in the far southeast to over 5 inches in parts of the far
western HSA.

At longer durations the picture is somewhat mixed as well.
November was much drier than average with a mean of 1.30 inches
across the network, with the southeast areas the driest. Only a
late month rain event prevented the driest November on record at
many locations and stopped a consecutive days with no rainfall
streak that was also approaching record duration at some sites.

Looking back 90 days there is a strong dry signal over the
southern sections of the HSA where many areas are at less than 50
percent of normal precipitation for that period, while parts of
the northwest are above 100 percent.

Drought:
Moderate drought (D1 drought category) continues to be shown on
the weekly U.S. Drought Monitor map across portions of southwest
Virginia and most of northwest North Carolina. Much of the
remainder of the HSA is in D0 or Abnormally Dry on the Drought
Monitor map. Southeast West Virginia remains free of any drought
designation.

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

Snow cover:
The recent snow event produced snowfall from just a couple of
inches in the far west up to 10 inches or more in the southeast
with liquid equivalent amounts ranging from less than 0.25 inches
in the far west up to about 1 inch in the far southeast. Most of
this snow is still in place due to the very cold temperatures in
recent days.

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

River ice:
There is little to no river ice as cold temperatures have only
recently occurred and are not expected to persist.

Streamflow:
Streamflows are also somewhat variable and reflect the general
precipitation patterns. Near to above normal flows are observed in
the west and north while river basins in the south show below to
much below normal flows. Several USGS stream gages in the Dan and
upper New River basins in far southern Virginia and northern North
Carolina are below the 10th percentile of all flows for this date
at durations ranging from 7 to 28 days.

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

Soil Moisture:
Rankings of soil moisture from the Climate Prediction Center
(CPC) show the driest soils are across far southwest Virginia and
northwest North Carolina with anomalies of 1 to nearly 2 inches.
Soils are closer to normal in most of the remainder of the HSA.

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

Reservoirs:
Major reservoirs are near guide curve with normal flood capacity
at the flood control reservoirs.

Future Weather Conditions:
Precipitation forecasts from the Weather Prediction Center (WPC)
over the next 7 days (through 12z Sunday January 16th) show
amounts ranging from less than 0.25 inches in the southeast up to
possibly 0.75 inches in the far northwest which is below normal
and very unlikely to produce any flooding. Temperatures will
modify very quickly over the next few days and erase the existing
snow cover in all areas. No flooding is expected to result from
this melt.

Longer term outlooks for the 6 to 10 and 8 to 14 day periods show
that temperatures are forecast to be well above average through
January 22nd. Precipitation is forecast to be above average during
that period but the highest chances for above average is west of
the HSA, across the lower Mississippi and Ohio valleys.

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

Probabilistic/Ensemble river forecasts:
The Meteorological Model Ensemble River Forecasts (MMEFS) through
January 15th indicate virtually no prospects for river flooding.
Minor rises are possible on the lower Dan and Roanoke Rivers as
the current snowpack melts but without significant rainfall
flooding is highly unlikely.

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

Summary:
The river flood potential is below average through January 19th,
2017.

Next issuance:
The next flood potential outlook will be issued on or around
January 19th, 2017.

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


$$

pc



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