Flood Potential Outlook
Issued by NWS Aberdeen, SD

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000 FGUS73 KABR 240919 ESFABR MNC011-155-SDC013-017-021-025-029-031-037-039-041-045-049-051-057- 059-065-069-075-085-089-091-107-109-115-117-119-129-221200- Probabilistic Hydrologic Outlook National Weather Service Aberdeen SD 418 AM CDT Sat Apr 24 2021 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: 04/24/2021 - 07/23/2021 : 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 8 <5 <5 <5 <5 :James River Columbia 13.0 16.0 18.0 : 10 38 6 27 <5 20 Stratford 14.0 17.0 18.5 : 26 50 10 33 5 19 :Snake Creek Ashton 11.5 13.0 16.0 : 10 23 6 16 5 6 :James River Ashton 13.0 14.0 16.0 : 13 42 13 41 12 29 :Turtle Creek Redfield 7.0 10.0 15.0 : 29 36 13 25 5 14 :James River Redfield 20.0 22.0 25.0 : 8 29 7 28 5 20 :Big Sioux River Watertown 10.0 11.0 12.0 : 6 8 <5 <5 <5 <5 Watertown Sioux C 9.0 10.0 12.0 : 13 23 6 10 <5 <5 Watertown Broadwa 10.5 11.0 13.5 : 21 35 16 29 5 5 Castlewood 9.0 11.0 16.0 : 25 44 13 18 <5 <5 :Grand River Little Eagle 15.0 17.0 21.0 : <5 <5 <5 <5 <5 <5 :Moreau River Whitehorse 21.0 23.0 25.0 : <5 <5 <5 <5 <5 <5 :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 8 <5 <5 <5 <5 :Minnesota River Big Stone Lake 971.5 973.0 975.0 : <5 <5 <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: 04/24/2021 - 07/23/2021 Location 95% 90% 75% 50% 25% 10% 5% -------- ------ ------ ------ ------ ------ ------ ------ :Elm River Westport 4.8 4.9 5.0 5.3 7.3 8.5 10.5 :James River Columbia 6.8 6.8 6.8 7.0 9.8 13.1 16.8 Stratford 8.2 8.2 8.2 8.3 14.2 17.1 18.4 :Snake Creek Ashton 3.0 3.0 3.0 3.9 6.8 11.4 14.9 :James River Ashton 6.6 6.6 6.6 6.6 8.8 16.4 20.3 :Turtle Creek Redfield 3.6 3.6 3.9 4.9 7.8 12.1 14.7 :James River Redfield 5.3 5.3 5.3 5.9 9.8 17.2 25.5 :Big Sioux River Watertown 4.5 4.5 5.0 6.7 8.0 9.4 10.3 Watertown Sioux C 3.9 3.9 4.3 5.6 6.8 9.3 10.6 Watertown Broadwa 5.6 5.6 6.3 7.7 9.4 11.6 13.1 Castlewood 5.4 5.4 6.0 7.2 8.9 11.4 12.4 :Grand River Little Eagle 3.0 3.2 4.5 5.3 7.1 7.8 8.6 :Moreau River Whitehorse 2.4 2.7 3.6 4.9 6.3 8.7 11.5 :Bad River Fort Pierre 1.0 1.0 2.5 6.0 9.8 15.2 17.9 :Little Minnesota River Peever 10.2 10.2 10.2 11.2 13.0 14.6 15.9 :Minnesota River Big Stone Lake 968.0 968.0 968.0 968.0 968.0 968.3 968.7 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: 04/24/2021 - 07/23/2021 Location 95% 90% 75% 50% 25% 10% 5% -------- ------ ------ ------ ------ ------ ------ ------ :Elm River Westport 4.6 4.6 4.6 4.6 4.5 3.9 3.1 :James River Columbia 6.2 5.9 5.0 4.7 4.6 4.5 4.5 Stratford 7.8 7.6 6.5 6.2 6.1 6.0 5.9 :Snake Creek Ashton 3.0 3.0 2.9 2.8 2.5 2.5 2.5 :James River Ashton 5.6 4.8 3.6 3.3 3.1 3.1 3.1 :Turtle Creek Redfield 3.4 3.4 3.4 3.4 3.3 3.3 3.3 :James River Redfield 5.1 4.7 3.8 3.3 3.2 3.1 3.1 :Big Sioux River Watertown 4.2 4.1 4.1 3.9 3.8 3.6 3.6 Watertown Sioux C 3.9 3.9 3.8 3.7 3.7 3.6 3.6 Watertown Broadwa 5.5 5.5 5.4 5.3 5.2 5.2 5.2 Castlewood 5.1 4.9 4.8 4.7 4.6 4.5 4.5 :Grand River Little Eagle 2.7 2.7 2.7 2.7 2.6 2.6 2.6 :Moreau River Whitehorse 2.2 2.2 2.2 2.2 2.1 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 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 late next month. $$ Parkin

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