Flood Potential Outlook
Issued by NWS Raleigh/Durham, NC

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Winter/Spring Flood Potential Outlook
National Weather Service Raleigh, NC
700 AM EST Fri Feb 2 2018

...THE CHANCE OF RIVER FLOODING OVER CENTRAL NC FOR THE WINTER/SPRING
IS SLIGHTLY BELOW NORMAL...

Precipitation Summary

The last two weeks of January featured 3 significant (>0.5 inches of
liquid water or equivalent) precipitation events. Most of the area
received significant snow (up to 10+ inches in some areas) on the
17th, which took a few days to melt and slowly infiltrate into the
soil. Liquid equivalent water ranged from 3 to 4 inches over almost
all of central NC - up to an inch above normal.

See www.water.weather.gov for detailed rainfall analysis.

Precipitation and departure from normal:

          Precipitation (inches) and departure from normal
            for the water year beginning 1 October 2017

    Month                RDU            GSO        Fayetteville
------------------------------------------------------------------

  October             4.29/ 1.04     3.03/-0.10     2.76/-0.45
  November            1.28/-1.84     0.95/-2.16     0.54/-2.23
  December            2.29/-0.78     1.60/-1.38     2.97/ 0.32
  January             3.92/ 0.42     3.65/ 0.59     3.08/-0.22

Total precip         11.78/-1.16     9.23/-3.05     9.35/-2.58
Percent normal            91             75             78
---------------------------------------------------------------

                  Begin     Actual   Normal  Departure  Percent
                  date       Pcpn     Pcpn   from norm  of norm

RALEIGH-DURHAM INTERNATIONAL AIRPORT (RDU)

 LAST   7 DAYS   01/26/2018   1.93    0.78      1.15      247%
 LAST  14 DAYS   01/19/2018   2.76    1.57      1.19      176%
 LAST  30 DAYS   01/03/2018   3.92    3.41      0.51      115%
 LAST  90 DAYS   11/04/2017   7.49    9.48     -1.99       79%
 LAST 180 DAYS   08/06/2017  19.06   20.96     -1.90       91%
 LAST 365 DAYS   02/02/2017  45.69   43.34      2.35      105%

PIEDMONT TRIAD INTERNATIONAL AIRPORT (GSO)

 LAST   7 DAYS   01/26/2018   1.31    0.67      0.64      196%
 LAST  14 DAYS   01/19/2018   1.71    1.35      0.36      127%
 LAST  30 DAYS   01/03/2018   3.69    2.98      0.71      124%
 LAST  90 DAYS   11/04/2017   6.24    8.92     -2.68       70%
 LAST 180 DAYS   08/06/2017  14.39   19.77     -5.38       73%
 LAST 365 DAYS   02/02/2017  41.40   42.20     -0.80       98%

FAYETTEVILLE AIRPORT (FAY)

 LAST   7 DAYS   01/26/2018   2.22    0.88      1.34      252%
 LAST  14 DAYS   01/19/2018   2.46    1.65      0.81      149%
 LAST  30 DAYS   01/03/2018   3.08    3.20     -0.12       96%
 LAST  90 DAYS   11/04/2017   6.59    8.57     -1.98       77%
 LAST 180 DAYS   08/06/2017  16.79   20.97     -4.18       80%
 LAST 365 DAYS   02/02/2017  42.45   44.46     -2.01       95%

Streamflow and lake levels

Streamflow on unregulated streams and rivers across central NC
showed marked improvement over the past week, although a number of
gages remain below normal.

See https://waterwatch.usgs.gov for additional details.

The major water supply and flood control reservoirs in central NC
are Falls Lake and B. Everett Jordan Lake, both operated by the U.S.
Army Corps of Engineers.

Falls Lake showed a one foot rise due to snowmelt from an event on
Jan 17th supplemented by heavy rain on Jan 28th. The lake level is
249.6 feet, which is ~2 feet below the target elevation of 251.5
feet.

B. Everett Jordan Lake showed a rise of 3 feet and is currently at
215.1 feet, which is 0.9 feet below the target elevation of 216
feet.

See www.epec.saw.usace.army.mil for additional details.

Short term forecast

The short term weather pattern features a long wave trof over the
eastern CONUS which favors rapid translation of weather systems
eastward. There are two potentially significant precipitation events
on the horizon, which should easily maintain or even further improve
our current state of abnormally dry (D0) to moderate drought (D1).

With the improvement in stream levels and soil moisture over the
past two weeks, a widespread 1-2 inch rainfall event would likely
cause limited minor river flooding.

Longer term precipitation outlook

We are currently in a weak to moderate La Nina phase of the El
Nino/Southern Oscillation (ENSO) cycle, which is expected to linger
through Spring. This is the `warm` ENSO phase, which typically
produces increased chances of warmer-than-normal temperatures and
less-than-normal precipitation. Given the persistent dryness in
place and unfavorable outlook for precipitation, the longer range
chance of river flooding is considered slightly below normal.

Additional details and discussion may be found at the Climate
Prediction Center website: http://www.cpc.ncep.noaa.gov

In summary, current hydrologic conditions are drier than normal
across central NC, but have shown improvement during the past 2
weeks.

There are a couple of systems in the near-term forecast which could
produce precipitation significant enough to cause minor river
flooding through mid February. There are no climatological signals
pointing towards higher-probabilty wet periods in the longer range
outlook. The chance of flooding through early Spring is slightly
below normal.

The next scheduled Winter/Spring flood outlook will be issued
on February 16th.

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

MLM



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