Flood Potential Outlook
Issued by NWS Aberdeen, SD

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000 FGUS73 KABR 252132 ESFABR MNC011-155-SDC013-017-021-025-029-031-037-039-041-045-049-051-057- 059-065-069-075-085-089-091-107-109-115-117-119-129-112200- Probabilistic Hydrologic Outlook National Weather Service Aberdeen SD 330 PM CST Thu Feb 25 2021 ...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. ...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 singificant 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 C 3.7 3.7 3.7 3.7 3.7 3.7 3.6 Watertown Broadwa 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. $$ Parkin

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