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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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