FGUS71 KRNK 170059
ESFRNK
NCC005-009-033-157-169-171-189-193-197-VAC005-009-011-017-019-021-
023-029-031-035-037-045-063-067-071-077-083-089-121-141-143-155-
161-163-173-185-197-530-580-590-640-678-680-690-750-770-775-
WVC025-055-063-089-240100-

Winter/Spring Flood Potential Outlook
National Weather Service Blacksburg VA
859 PM EDT Thu Mar 16 2023

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

...River Flood Potential is Near Average/Normal...

Each winter and early spring, the National Weather Service office
in Blacksburg, Virginia issues a series of routine flood
potential outlooks. These outlooks estimate the potential for
river flooding (not flash flooding) across the Blacksburg
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, streamflows, 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. Snowmelt can contribute to the flooding as it did
dramatically in January 1996 when rain on top of rapid snowmelt
produced record flooding throughout parts of the Mid Atlantic
region, including the Greenbrier River.

Flood Potential Outlook: For the Blacksburg HSA, the river flood
potential is near average/normal for the next two weeks (through
March 30).

Precipitation over the winter has been frequent, making for
streamflows and soil moisture mainly in the normal range. More
recently, the passage of multiple low pressure systems during the
middle of February resulted in rounds of prolonged and some-
times heavy precipitation, as well as minor river flooding in the
New, the upper James and the Clinch basins. Since then however,
precipitation has been below normal for most of the HSA, resulting
in decreased stream flows and soil moisture. Remaining snow cover
is hydrologically insignificant to produce river flooding, and no
frozen ground or river ice exists within the HSA. Streamflows and
soil moisture are generally in the normal range. There are no
storms systems expected within the next 7 days that will be
capable of producing river flooding, though precipitation in the 
6-10 and the 8-14 day periods are expected to be above normal.


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

Recent Precipitation: Precipitation through the month of March has
generally been below-normal for most of the HSA, particularly for
portions of the southern Piedmont of Virginia, where precipitation
totals have ranged from 0.75 to 1.0 inches, or between 20 to 30
percent of normal. Only localized area have received above-normal
precipitation during the month, particularly along the crest of
the Blue Ridge and portions of the New River Valley, each of 
which has received amounts ranging from 100 to 150 percent of 
normal.
 

During February, rainfall ranging from one quarter to two-thirds
of an inch was observed on February 1-2. On February 11-12, a 
deep low pressure system triggered widespread precipitation 
ranging from 1.5 to 2.5 inches, which brought several rivers to 
near- bankfull. This was followed by 1.5 to 2.5 inches of rainfall
on February 16-17 from the Alleghany Highlands through southeast 
West Virginia and western Virginia that resulted in minor flooding
along portions of several rivers, including the Clinch, the 
Bluestone, the East, the Cowpasture and the Greenbrier Rivers. 
Only modest precipitation was observed through the remainder of 
the month.

For January 2023, precipitation ranged between 2 to 3 inches
across the mountains north of Highway 460, and between 3 and 5
inches elsewhere within the HSA. Looking at the extremes, the
driest area was the upper James basin, with amounts that were less
than 75 percent of normal, while pockets of the Roanoke and Dan
River basins recorded amounts that were over 125 percent of
normal. Precipitation elsewhere within the HSA was within 25
percent of normal. Precipitation events were light in intensity
through the month and usually spaced 1-3 days apart. Nearly all
precipitation fell in the form of rain. No flooding was reported.

For December 2022, precipitation fell mainly in the form of rain,
and ranged between 3 and 5 inches for the eastern three quarters
of the HSA. These amounts were anywhere between 75 and 125 percent
of normal. The western-most quarter of the HSA was driest, which
includes the mountains from western Greenbrier County through
Watauga County, where only 2 to 3 inches of precipitation were
observed. These amounts were anywhere between 50 and 75 percent of
normal.

 
Drought: The March 14, 2023 rendition of the weekly U.S. Drought 
Monitor (issued March 16) indicates no drought or abnormally dry 
conditions anywhere within the HSA.

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

Snow cover: The only snow cover remaining within the HSA is
confined to the higher ridgetops of mainly the New River basin,
from southeast West Virginia to the Highlands of North Carolina.
The remaining snow cover is hydrologically insignificant however,
with depths of 2 inches or less as of the morning of March 16.
Snow depth continues to diminish rapidly.

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


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

Streamflows: Average streamflows for much of the HSA are in the
normal range at the 7-, 14-, and 28-day timeframes. The exception
is for locations east of the Highway 29 corridor of central
Virginia, as well as portions of the upper James River basin,
where streamflows are slightly below-normal for those
same timeframes.

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

Soil Moisture: Per the Climate Prediction Center, soil moisture
across nearly all of the HSA is near-normal, with localized areas
where moisture is slightly below-normal.

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, Smith Mountain Lake,
and the Western VA Water Authority reservoirs near Roanoke are
near full capacity and guide curves where applicable.

Future Weather Conditions: Precipitation amounts through March 23
are expected to be 0.50 inch or less across most of the HSA, with
locally higher amounts possible.

The WPC Quantitative Precipitation Forecast is updated frequently
and is available at: www.wpc.ncep.noaa.gov/#page=qpf
 
The 6 to 10 day outlook from the NWS Climate Prediction Center
during the period March 21-25 indicates a weather pattern where
temperatures are favored to be below-normal, while precipitation
is favored to be above-normal.

The 8 to 14 day outlook from March 23-29 indicates a weather
pattern where temperatures are likely to be near-normal, and
precipitation is favored to be above-normal.

 
Probabilistic/Ensemble river forecasts: The Meteorological Model
Ensemble River Forecasts (MMEFS) valid through about March 25
indicate that all rivers will remain below bankfull, although
within-bank rises are likely.

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

Summary: Flood Potential Outlook: For the Blacksburg HSA, the
river flood potential is near average/normal for the next two
weeks (through March 30).

Next issuance: This is expected to be the final winter/spring
flood potential outlook of the 2023 season.

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


$$

NF/WP
$$