National Weather Service United States Department of Commerce
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.

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

The outlook for the next two weeks is for increased chances for above
normal temperatures and below normal precipitation. The 30 day
outlook for March calls for equal chances of below, near, or above
normal temperatures and precipitation. The 90 day outlook for March
through May shows a higher chance for above normal temperatures,
along with equal chances of below, near, or above normal
precipitation.

Current Snow Conditions

The snow pack has pretty much melted across the region except for
some remaining snow cover in ditches and shelterbelts.

Modeled Snow Depth (2/25/21)



Modeled Snow Water Equivalent (2/25/21)



Current Soil Conditions

Soil moisture is below normal across the entire region, with
anomalies currently running around 2 to 3 inches below normal. Soils
are generally frozen to 1 to 2.5 feet. Even with significant frozen
soil, the fact that the soils have been so 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 flows are generally near normal to below normal
across the region. Most rivers have seen increasing ice formation
with the cold weather earlier in February. Most reports are showing
one to two feet of ice thickness on the rivers and streams. The
threat for break-up ice jams does exist as we head into spring, but
the threat is normal to below normal due to lower flows on the rivers
and streams. The ice jam threat will continue to decrease if we
continue to melt the ice without adding any significant flow to the
rivers that would raise and break up the ice, allowing it to flow
downstream where it could jam.
Probabilistic Outlooks



In Table 1 below...the current (CS) and historical (HS) or normal
probabilities of exceeding minor...moderate...and major flood stages
are listed for the valid time period.

CS values indicate the probability of reaching a flood category
based on current conditions.

HS values indicate the probability of reaching a flood category
based on historical or normal conditions.

When the value of CS is more than HS...the probability of
exceeding that level is higher than normal. When the value of CS is
less than HS...the probability of exceeding that level is lower
than normal.


...Table 1--Probabilities for minor...moderate and major flooding...
                    Valid Period:  02/28/2021  - 05/29/2021

                                       :    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 :  20   45   15   34   10   26
Stratford           14.0   17.0   18.5 :  27   47   14   37    8   23
:Snake Creek
Ashton              11.5   13.0   16.0 :   9   31    8   27    5   17
:James River
Ashton              13.0   14.0   16.0 :  16   38   13   37   10   31
:Turtle Creek
Redfield             7.0   10.0   15.0 :  17   30    9   22    5   14
:James River
Redfield            20.0   22.0   25.0 :   8   28    7   27    6   26
:Big Sioux River
Watertown           10.0   11.0   12.0 :  20   24    5   16   <5    6
Watertown Sioux C    9.0   10.0   12.0 :  37   34   11   26   <5    9
Watertown Broadwa   10.5   11.0   13.5 :  44   37   35   34   <5   15
Castlewood           9.0   11.0   16.0 :  45   39   18   27   <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: 02/28/2021  - 05/29/2021
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Elm River
Westport              4.8    4.8    5.0    5.4    6.5    9.5   13.5
:James River
Columbia              5.7    5.7    5.8    6.9   11.8   18.0   19.4
Stratford             6.9    6.9    7.0    9.2   14.2   17.6   20.0
:Snake Creek
Ashton                2.5    2.5    2.9    4.4    6.2    9.6   16.3
:James River
Ashton                4.1    4.1    4.6    6.0    9.0   15.8   24.9
:Turtle Creek
Redfield              3.4    3.4    3.5    4.3    5.7    9.6   14.4
:James River
Redfield              4.0    4.0    4.5    6.0   10.2   16.6   28.2
:Big Sioux River
Watertown             5.6    6.1    6.6    8.8    9.6   10.5   10.9
Watertown Sioux C     5.0    5.2    5.7    8.4    9.5   10.2   10.8
Watertown Broadwa     6.2    6.6    7.1   10.2   11.2   12.7   13.0
Castlewood            5.5    5.6    6.0    8.8   10.2   12.1   12.7
:Grand River
Little Eagle          3.1    3.1    3.7    5.5    7.1    9.4   11.0
:Moreau River
Whitehorse            2.4    2.5    3.5    5.1    7.9   10.8   12.9
:Bad River
Fort Pierre           1.1    2.0    3.5    5.3    7.9   11.6   15.5
:Little Minnesota River
Peever               10.6   10.6   11.1   12.1   13.1   15.2   16.1
:Minnesota River
Big Stone Lake      967.6  967.7  968.0  968.0  968.0  968.2  968.5

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: 02/28/2021  - 05/29/2021
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Elm River
Westport              4.6    4.5    4.5    4.5    4.5    4.5    4.4
:James River
Columbia              5.6    5.5    5.5    5.4    5.3    5.2    5.2
Stratford             6.8    6.8    6.8    6.6    6.5    6.4    6.4
:Snake Creek
Ashton                2.5    2.5    2.5    2.5    2.5    2.5    2.5
:James River
Ashton                4.1    4.1    4.1    4.0    3.7    3.6    3.6
:Turtle Creek
Redfield              3.3    3.3    3.3    3.3    3.2    3.2    3.2
:James River
Redfield              4.0    4.0    3.9    3.8    3.6    3.5    3.5
:Big Sioux River
Watertown             4.0    4.0    4.0    4.0    4.0    4.0    4.0
Watertown Sioux Conif 3.7    3.7    3.7    3.7    3.7    3.7    3.6
Watertown Broadway    5.2    5.2    5.2    5.2    5.2    5.2    5.2
Castlewood            4.7    4.7    4.7    4.7    4.7    4.6    4.6
:Grand River
Little Eagle          3.0    3.0    3.0    3.0    2.8    2.8    2.8
:Moreau River
Whitehorse            2.2    2.2    2.2    2.2    2.2    2.2    2.1
:Bad River
Fort Pierre           1.0    1.0    1.0    1.0    1.0    1.0    1.0
:Little Minnesota River
Peever               10.1    9.7    9.7    9.7    9.7    9.7    9.7
:Minnesota River
Big Stone Lake      967.2  967.2  967.2  967.2  967.2  967.2  967.2

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.

The next outlook will be issued on Thursday, March 11th.