Flood Potential Outlook
Issued by NWS Blacksburg, VA

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Winter/Spring Flood Potential Outlook
National Weather Service Blacksburg VA
1015 AM EST Thu Feb 16 2017

...Winter/Spring Flood Outlook...Number 4

...River flood potential below normal through end of February...

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 entire two week outlook period (through March 2nd). No
heavy rain is forecast over the next seven days and there is no
snowmelt potential.

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

Recent Precipitation:
February has turned much drier after a wet January. Precipitation
across the HSA so far this month has ranged generally from 0.25
to 0.75 inches with a few higher and lower amounts. The driest
area has been across portions of the James River basin where
numerous stations have seen less than 0.20 inches so far this
month. Hot Springs COOP station in Bath County has seen only .01
inches this month.

January precipitation was generally near or above normal across
the HSA ranging from 3 to 5 inches with some slightly higher and
lower amounts. It was somewhat wetter in the western mountains
with the driest area in the northern Blue Ridge of Virginia. The
NWS network of Cooperative and ASOS gages (57 sites) had an
average of 4.23 inches of precipitation versus the long- term
normal (1981-2010) of 3.32 inches or 127 percent of normal.

December precipitation was near normal with a mean of 3.28 inches
or 99 percent of normal. There was a wide 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. 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 from mid-November through mid-February there
is persistent dry signal over southeastern portions of the HSA
where some stations are at 50 to 75 percent of normal
precipitation for that period. Meanwhile parts of the northwest
HSA (mainly in WV and far western VA) are at 110 to 125 percent
of normal precipitation for the period.

Drought:
The dry weather over the past 3 weeks has resulted in a
reintroduction of the Abnormally Dry (D0) category from about the
Blue Ridge eastward on the latest U.S. Drought Monitor (issued
February 16th, valid through February 14th). No area is currently
in Moderate Drought (D1) on the Drought Monitor.

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

Snow cover:
Small amounts of high elevation snow in the western mountains
will be gone in a day or two.

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

River ice:
There is no river ice as winter temperatures have been well above
normal. January was 4 to 7 degrees above the long-term average
average and February has been very mild with temperatures about 7
degrees above normal through mid-month.

Streamflow:
Streamflows generally reflect the recent dry pattern with below
normal flows at shorter durations (daily to 14 days). Some USGS
gaging stations have fallen below the 10th percentile of all
flows for this date. At longer durations the flows are closer to
normal due to the wetter conditions that occurred in January.

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)
show a swath of below normal values extending from northwest
North Carolina northeast through the Blue Ridge foothills and
piedmont of both Virginia and North Carolina. Anomalies are
around 1 inch within this area as of February 15th.

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

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

Future Weather Conditions:
Quantitative precipitation forecasts (QPF) from the Weather
Prediction Center (WPC) over the next 7 days (through 12z
Thursday February 23rd) show amounts ranging from less than 0.10
inches in the eastern piedmont up to about 0.50 inches in the far
west. The primary storm track over the next week will be well
south of the HSA with the heaviest rain expected over parts of
the Gulf coast and also in the western U.S.

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 1st show a high likelihood of temperatures
continuing to be above normal through the entire period.
There is an increased probability of above normal precipitation
through the period.

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 February 23rd indicate 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 average through the outlook
period, based on current conditions and forecasts.

Next issuance:
The next flood potential outlook will be issued on or around
March 2nd, 2017.

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


$$

PC



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