Spring Flood Outlook

This spring flood outlook is for the rivers and streams in northeast
South Dakota, portions of central South Dakota, and portions of west
central Minnesota.

Due to the very dry conditions across the area this winter and the
lack of any significant snow cover, the chances for minor, moderate
or major flooding are below normal this spring. Probablilities for
flooding continue to decrease, with some locations up to 25 percent
lower than they were two weeks ago on the last outlook.

The flood threat through this spring, both in location and severity,
will be determined by future rain and future snowfall.

The outlook for the next two weeks shows that there is a higher
chance for below normal temperatures and precipitation. The 90 day
outlook for March through May shows a higher chance for above normal
temperatures, along with normal to below normal precipitation.

Current Snow Conditions

The current snowpack is all from the snow that fell on March 10th,
and is generally south and east of a line from Leola to Hayes. Snow
depths range from 2 to 8 inches. The water equivalent is generally
0.75 inches or less.

Modeled Snow Depth (3/11/21)



Modeled Snow Water Equivalent (2/25/21)

Current Soil Conditions

Soil moisture is below normal across the region, with anomalies
running around 2 to 4 inches below normal. Soils are frozen to a
depth of 1 to 3 feet across the area. Even with frozen soils, the
fact that the soils have been dry will limit the impact the frost
will have on infiltration and runoff during the snowmelt and early
spring rains.

Current River Conditions

River levels and flow are generally near normal to below normal
across the region. Most rivers are now at least partly ice free after
the recent very warm stretch that saw temperatures averaging 15 to 30
degrees above normal. This has significantly lowered the risk of ice
jam flooding as we go into the spring.

Probabilistic Outlooks

...Table 1--Probabilities for minor...moderate and major flooding...
                    Valid Period:  03/14/2021  - 06/12/2021

                                       :    Current and Historical
                                       :     Chances of Exceeding
                                       :       Flood Categories
                                       :      as a Percentage (%)
                      Categorical      :
                   Flood Stages (FT)   :   Minor    Moderate   Major
Location           Minor   Mod   Major :  CS   HS   CS   HS   CS   HS
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:Elm River
Westport            14.0   16.0   19.0 :  <5   19   <5    8   <5    5
:James River
Columbia            13.0   16.0   18.0 :  14   45   10   34    9   26
Stratford           14.0   17.0   18.5 :  19   47   11   37    8   23
:Snake Creek
Ashton              11.5   13.0   16.0 :  12   34   11   30    5   17
:James River
Ashton              13.0   14.0   16.0 :  16   41   14   40   12   31
:Turtle Creek
Redfield             7.0   10.0   15.0 :  18   33   13   25    8   17
:James River
Redfield            20.0   22.0   25.0 :  12   31   11   30    9   26
:Big Sioux River
Watertown           10.0   11.0   12.0 :   5   24   <5   16   <5    6
Watertown Sioux C    9.0   10.0   12.0 :  13   36   <5   28   <5    9
Watertown Broadwa   10.5   11.0   13.5 :  17   40   14   37   <5   15
Castlewood           9.0   11.0   16.0 :  17   46    7   30   <5   <5
:Grand River
Little Eagle        15.0   17.0   21.0 :  <5   12   <5   10   <5   <5
:Moreau River
Whitehorse          21.0   23.0   25.0 :  <5    9   <5    7   <5    6
:Bad River
Fort Pierre         21.0   25.0   27.0 :  <5    5   <5   <5   <5   <5
:Little Minnesota River
Peever              17.0   22.0   24.0 :  <5   25   <5   <5   <5   <5
:Minnesota River
Big Stone Lake     971.5  973.0  975.0 :  <5    6   <5   <5   <5   <5

Legend
CS = Conditional Simulation (Current Outlook)
HS = Historical Simulation
FT = Feet

In Table 2 below...the 95 through 5 percent columns indicate the
probability of exceeding the listed stage levels (FT) for the valid
time period.

...Table 2--Exceedance Probabilities...

                               Chance of Exceeding Stages
                                  at Specific Locations
                          Valid Period: 03/14/2021  - 06/12/2021
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Elm River
Westport              4.8    4.8    5.0    5.2    6.3    9.7   13.0
:James River
Columbia              5.7    5.7    5.7    6.4   10.8   16.0   19.3
Stratford             6.8    6.8    6.8    7.8   12.3   17.5   19.9
:Snake Creek
Ashton                2.5    2.5    3.1    4.0    6.3   13.2   16.5
:James River
Ashton                4.2    4.2    4.2    4.9    7.5   17.2   24.6
:Turtle Creek
Redfield              3.2    3.2    3.5    4.4    5.5   13.0   16.0
:James River
Redfield              4.0    4.0    4.1    5.1    7.9   23.8   28.4
:Big Sioux River
Watertown             4.5    4.7    5.8    6.5    8.2    9.7   10.0
Watertown Sioux C     3.7    4.0    4.6    5.2    6.7    9.7    9.9
Watertown Broadwa     5.4    5.6    6.3    7.4    9.0   12.0   12.5
Castlewood            4.7    4.8    5.4    6.4    8.1   10.7   11.4
:Grand River
Little Eagle          3.1    3.1    3.4    5.3    7.6    9.8   10.4
:Moreau River
Whitehorse            3.0    3.0    3.4    5.2    7.5   11.4   13.8
:Bad River
Fort Pierre           1.1    1.2    3.2    6.2   11.4   16.5   19.0
:Little Minnesota River
Peever               10.8   10.8   10.8   11.8   12.9   15.0   16.0
:Minnesota River
Big Stone Lake      967.7  967.8  967.9  968.0  968.0  968.1  968.3

In Table 3 below...the 95 through 5 percent columns indicate the
probability of falling below the listed stage levels (FT) for the
valid time period.

...Table 3--Nonexceedance Probabilities...

                            Chance of Falling Below Stages
                                 at Specific Locations
                          Valid Period: 03/14/2021  - 06/12/2021
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Elm River
Westport              4.6    4.5    4.5    4.5    4.5    4.4    4.4
:James River
Columbia              5.6    5.5    5.4    5.1    4.9    4.9    4.9
Stratford             6.8    6.8    6.7    6.5    6.4    6.3    6.3
:Snake Creek
Ashton                2.5    2.5    2.5    2.5    2.5    2.5    2.5
:James River
Ashton                4.1    4.1    4.0    3.5    3.4    3.3    3.3
:Turtle Creek
Redfield              3.1    3.1    3.1    3.1    3.0    3.0    3.0
:James River
Redfield              3.9    3.9    3.8    3.4    3.2    3.2    3.1
:Big Sioux River
Watertown             4.1    4.1    4.1    4.0    3.9    3.7    3.6
Watertown Sioux C     3.6    3.6    3.6    3.6    3.6    3.6    3.6
Watertown Broadwa     5.2    5.2    5.2    5.2    5.2    5.1    5.1
Castlewood            4.6    4.6    4.6    4.5    4.5    4.3    4.3
:Grand River
Little Eagle          3.0    3.0    3.0    2.9    2.8    2.8    2.7
:Moreau River
Whitehorse            2.3    2.3    2.2    2.2    2.2    2.1    2.1
:Bad River
Fort Pierre           1.0    1.0    1.0    1.0    1.0    1.0    1.0
:Little Minnesota River
Peever                9.7    9.7    9.7    9.7    9.7    9.7    9.7
:Minnesota River
Big Stone Lake      967.4  967.4  967.4  967.4  967.4  967.4  967.4

These long-range probabilistic outlooks contain forecast values that
are calculated using multiple season scenarios from 30 or more years
of climatological data...including current conditions of the
river...soil moisture...snow cover...and 30 to 90 day long-range
outlooks of temperature and precipitation. By providing a range of
probabilities...the level of risk associated with long-range planning
decisions can be determined. These probabilistic forecasts are part
of the National Weather Service`s advanced hydrologic prediction
service.

Visit our web site weather.gov/abr for more weather and water
information.