Back-to-back powerful Pacific storm systems to impact the Pacific Northwest and northern California through the end of this week with heavy rain, flooding, strong winds, and higher elevation mountain snow. A strong, long-duration atmospheric river will accompany the Pacific storms, bringing excessive rainfall and flash flooding to southwest Oregon and northwest California through the week. Read More >
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.
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