2020 Spring Flood Outlook
Issued on March 12th, 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 conditons 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 below normal
temperatures. The 90 day outlook for March through May shows equal
chances for below, near, or 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 (3/12/20)
Modeled Snow Water Equivalent (3/12/20)
Current snow conditions
Snow depths have decreased significantly across the are since the
last outlook. There is generally 4 to 8 inches on the ground in the
Watertown area, from north of Highmore to west of Gettysburg, as well
as along the just south of the North Dakota/South Dakota border.
Little to no snow cover exists elsewhere. The water equivalent of the
snow pack is generally a trace to around 2 inches.
Current soil conditions
Frost depths are generally in the 3 inch to 2 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
There is still some ice cover on many of the rivers, especially along
and east of the James River Valley, but chances for ice jam flooding
have decreased. River levels and flows are generally running above
normal across the region.
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: 03/14/2020 - 06/12/2020
: 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 : 27 19 16 8 <5 5
:James River
Columbia 13.0 16.0 18.0 : >98 45 >98 34 >98 26
Stratford 14.0 17.0 18.5 : >98 47 >98 37 92 23
Ashton 13.0 14.0 16.0 : >98 46 >98 44 >98 35
:Turtle Creek
Redfield 7.0 10.0 15.0 : >98 33 47 25 16 17
:James River
Redfield 20.0 22.0 25.0 : 89 32 68 30 46 28
:Big Sioux River
Watertown 10.0 11.0 12.0 : 30 33 9 17 <5 6
Watertown Sioux C 9.0 10.0 12.0 : 96 57 66 44 16 27
Watertown Broadwa 10.5 11.0 13.5 : 61 40 44 37 <5 15
Castlewood 9.0 11.0 16.0 : 72 46 34 30 <5 <5
:Grand River
Little Eagle 15.0 17.0 21.0 : 20 12 5 10 <5 <5
:Moreau River
Whitehorse 21.0 23.0 25.0 : 10 9 5 7 <5 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 : 48 24 <5 <5 <5 <5
:Minnesota River
Big Stone Lake 971.5 973.0 975.0 : 10 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: 03/14/2020 - 06/12/2020
Location 95% 90% 75% 50% 25% 10% 5%
-------- ------ ------ ------ ------ ------ ------ ------
:Elm River
Westport 9.0 9.4 10.0 11.8 14.2 18.0 18.7
:James River
Columbia 18.6 18.9 19.1 19.4 19.8 20.7 20.9
Stratford 18.4 18.6 19.0 19.4 20.0 21.1 21.5
Ashton 18.7 19.6 20.4 21.9 24.0 27.8 32.2
:Turtle Creek
Redfield 8.9 8.9 8.9 9.8 11.6 17.0 17.7
:James River
Redfield 18.6 19.8 21.4 24.8 28.7 32.9 33.7
:Big Sioux River
Watertown 8.1 8.4 8.5 9.0 10.2 10.8 11.3
Watertown Sioux C 9.1 9.4 9.7 10.3 11.6 12.7 13.3
Watertown Broadwa 9.2 9.5 9.7 10.7 12.1 13.1 13.3
Castlewood 8.0 8.3 8.5 10.0 11.2 12.4 12.8
:Grand River
Little Eagle 5.7 5.7 6.7 9.5 12.7 16.3 17.1
:Moreau River
Whitehorse 6.2 6.2 6.2 11.4 14.6 21.1 23.6
:Bad River
Fort Pierre 1.1 1.5 3.8 8.4 14.1 20.0 22.8
:Little Minnesota River
Peever 13.9 14.0 15.1 16.9 19.0 20.9 22.0
:Minnesota River
Big Stone Lake 968.8 968.8 968.8 968.9 969.8 971.5 972.5
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: 03/14/2020 - 06/12/2020
Location 95% 90% 75% 50% 25% 10% 5%
-------- ------ ------ ------ ------ ------ ------ ------
:Elm River
Westport 5.6 5.5 5.2 5.1 5.0 5.0 5.0
:James River
Columbia 15.3 15.3 15.3 12.9 10.7 10.3 9.6
Stratford 16.8 16.6 16.4 15.0 12.8 12.1 11.9
Ashton 15.7 15.6 14.7 10.8 8.6 7.8 7.5
:Turtle Creek
Redfield 4.7 4.4 4.1 4.0 3.6 3.6 3.5
:James River
Redfield 14.7 14.2 12.5 9.8 8.2 7.4 7.1
:Big Sioux River
Watertown 4.9 4.8 4.7 4.6 4.6 4.5 4.5
Watertown Sioux C 7.3 6.9 6.5 6.2 6.2 6.2 6.2
Watertown Broadwa 7.2 6.6 6.1 5.9 5.8 5.8 5.8
Castlewood 6.0 5.6 5.2 5.0 4.9 4.8 4.8
:Grand River
Little Eagle 3.4 3.4 3.3 3.3 3.2 3.2 3.2
:Moreau River
Whitehorse 2.8 2.7 2.6 2.5 2.4 2.4 2.3
:Bad River
Fort Pierre 1.0 1.0 1.0 1.0 1.0 1.0 1.0
:Little Minnesota River
Peever 11.0 10.8 10.6 10.4 10.3 10.0 9.6
:Minnesota River
Big Stone Lake 968.0 968.0 968.0 968.0 968.0 968.0 968.0
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 March 26th, 2020.
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