National Weather Service United States Department of Commerce
2020 Spring Flood Outlook
Issued on February 13, 2020
This spring flood outlook is for the rivers and streams in
northeastern South Dakota, portions of central South Dakota, and
portions of west central Minnesota.

Due to the very wet conditions across the area late last summer and
into last fall, the chances for minor, moderate, or major flooding
are above normal across the eastern and central parts of the area,
with lesser chances across the west.

The flood threat through this spring, both in location and severity,
will be determined by future rain or snowfall, and how fast the
melting of the snowpack occurs.

The outlook for the next two weeks is for higher chances for below
normal precipitation, and higher chances for above normal
temperatures. The 90 day outlook through the end of April shows
higher chances for above normal precipitation and temperatures.

The chances for river flooding are near to above normal, with well
above normal chances for the James River and Big Sioux River basins.
Current snow conditions

Modeled Snow Depth (2/13/20)



Modeled Snow Water Equivalent (2/13/20)



There is a wide range of snow depths across the area. They generally
range from a trace to 4 inches west of the Missouri River, 4 to 9
inches between the Missouri River Valley and the James River Valley,
to 5 to 16 inches east of the James River Valley. The water
equivalent of the snow pack is generally a trace to 1 inch west of
the Missouri River, a trace to 2 inches between the Missouri River
Valley and the James River Valley, to 2 to 5 inches east of the James
River Valley.

Current soil conditions

Frost depths are generally in the 1 to 2.5 foot range. With wet
conditions last fall heading into the freeze-up, the soils were
fairly well saturated as they froze, which will make them much more
impervious to soaking up much of the snow melt as it occurs.
Current river conditions
The majority of the rivers in the area are iced over. River levels
and flows are generally running near to above normal across the
region, or estimated to be so where the rivers are frozen. Ice jams
are possible as we head into the spring, as the increased flows will
raise and break up the river ice before it melts.
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:  02/15/2020  - 05/15/2020

                                       :    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 :  81   19   61    8   35    5
:James River
Columbia            13.0   16.0   18.0 : >98   45  >98   34  >98   24
Stratford           14.0   17.0   18.5 : >98   46  >98   37  >98   23
Ashton              13.0   14.0   16.0 : >98   38  >98   37  >98   31
:Turtle Creek
Redfield             7.0   10.0   15.0 : >98   30  >98   22   41   14
:James River
Redfield            20.0   22.0   25.0 : >98   28  >98   27   95   26
:Big Sioux River
Watertown           10.0   11.0   12.0 :  95   32   63   18   11    6
Watertown            8.0   10.0   12.0 : >98   43   80   26   14   10
Watertown - Broad   11.0   14.0   16.0 : >98   34    9    7   <5   <5
Castlewood           9.0   11.0   16.0 : >98   39   86   27   <5   <5
:Grand River
Little Eagle        15.0   17.0   21.0 :  25   12   13   10   <5   <5
:Moreau River
Whitehorse          21.0   23.0   25.0 :  17    9    9    7    7    6
:Bad River
Fort Pierre         21.0   25.0   27.0 :   8   <5   <5   <5   <5   <5
:Little Minnesota River
Peever              17.0   22.0   24.0 : >95   23   18   <5   <5   <5
:Minnesota River
Big Stone Lake     971.5  973.0  975.0 :  36    6   16   <5    6   <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: 02/15/2020  - 05/15/2020
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Elm River
Westport             12.0   13.1   14.7   18.0   20.2   21.2   22.3
:James River
Columbia             19.1   19.2   19.4   19.8   20.4   20.6   21.1
Stratford            19.5   19.6   19.8   20.2   20.6   21.1   21.4
Ashton               21.8   22.7   23.2   24.6   25.8   28.7   30.3
:Turtle Creek
Redfield             10.6   11.2   12.4   14.1   15.9   17.0   18.3
:James River
Redfield             25.0   25.6   27.0   31.3   32.6   33.6   33.9
:Big Sioux River
Watertown             9.9   10.2   10.7   11.3   11.6   12.1   12.3
Watertown             9.6    9.8   10.2   11.1   11.6   12.4   12.6
Watertown - Broad    11.5   11.7   12.4   13.0   13.3   14.0   14.4
Castlewood           10.5   10.7   11.3   12.1   12.6   13.4   13.8
:Grand River
Little Eagle          6.3    7.8    9.3   10.9   15.0   17.3   18.5
:Moreau River
Whitehorse            9.1   10.4   11.8   14.3   16.8   22.5   27.1
:Bad River
Fort Pierre           5.0    6.3    9.2   11.4   15.7   20.3   23.1
:Little Minnesota River
Peever               17.3   17.7   19.0   20.2   21.7   22.5   23.9
:Minnesota River
Big Stone Lake      968.6  969.2  969.9  970.8  972.2  974.3  975.7

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: 02/15/2020  - 05/15/2020
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Elm River
Westport              3.0    3.0    3.0    3.0    3.0    3.0    3.0
:James River
Columbia             11.8   11.8   11.8   10.9   10.7   10.7   10.6
Stratford            12.8   12.8   12.8   12.8   12.3   12.0   11.9
Ashton                8.2    8.1    8.1    8.1    8.1    8.1    8.1
:Turtle Creek
Redfield              3.4    3.4    3.3    3.3    3.3    3.3    3.3
:James River
Redfield              7.4    7.3    7.3    7.3    7.3    7.3    7.3
:Big Sioux River
Watertown             4.6    4.6    4.6    4.6    4.6    4.6    4.6
Watertown             4.7    4.7    4.7    4.7    4.6    4.6    4.6
Watertown - Broad     5.8    5.8    5.8    5.8    5.8    5.8    5.8
Castlewood            4.9    4.9    4.9    4.9    4.9    4.9    4.9
:Grand River
Little Eagle          3.6    3.6    3.3    3.3    3.2    3.2    3.1
:Moreau River
Whitehorse            2.8    2.8    2.7    2.6    2.5    2.4    2.4
:Bad River
Fort Pierre           1.4    1.1    1.1    1.0    1.0    1.0    1.0
:Little Minnesota River
Peever               10.5   10.5   10.5   10.4   10.4   10.3   10.3
: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.

The next outlook will be issued on February 27th.