####018009995#### FGUS73 KUNR 141417 ESFUNR Probabilistic Hydrologic Outlook National Weather Service Rapid City SD 816 AM MST Thu Mar 14 2024 ...Spring Flood and Water Resource Outlook... ...Below-Average Flood Potential This Spring... This spring flood and water resource outlook is for the Rapid City Hydrologic Service Area (HSA), which covers northeastern Wyoming and western South Dakota. The main river basins include the Little Missouri, eastern Powder, Belle Fourche, Grand, Moreau, Cheyenne, Bad, White, and Keya Paha. .Flood Outlook Summary... The flood potential this spring is below average across all of northeastern Wyoming and western South Dakota. Ice cover that is on the higher elevation lakes will continue to melt over the next few weeks. Ice jam flooding is not expected this year. River-ice breakup and the potential for ice-jam flooding usually occurs in late February and March. Flooding from snowmelt on the plains typically occurs between March and May, while snowmelt flooding is later in the Black Hills. The potential for rainfall- induced flash flooding is not quantifiable because this type of flooding is usually caused by localized thunderstorms during the spring and summer. The flood potential is still very dependent on weather conditions this spring. The amount of additional snow and rain, as well as the timing of peak river and stream flows, will have a significant effect on the severity of flooding. .Temperatures and Precipitation... Temperatures so far this winter have been very warm and above average. To date, Rapid City is the 6th warmest on record with an average temperature of 37.3 degrees. The average temperature in Gillette has been 35.1 degrees, making it the 5th warmest winter. Precipitation since December has been slightly below average. Snowfall this winter season for Rapid City has been 13.1 inches and 13.3 inches in Gillette. .Snow Cover and Liquid Water Content... Snow cover across the area is below average. There is still a little snow in the Black Hills, but amounts are minimal. Snow water equivalent is more than half of average for this time of year. The halfway point of the snow season was February 1, but March and April are typically snowy months, which is when a third of the annual snowfall occurs. The median peak snow water equivalent in the Black Hills usually occurs around April 1. .Soil Conditions and Frost Depths... Melting snow along with the thawed ground has helped to replenish moisture in the top layers of the ground. Soil moisture is slightly above average across south-central South Dakota, with below-average soil moisture in moderate and severe drought areas. The only frost remaining in the ground is over northwestern South Dakota and higher elevations of the Black Hills. Frost depths in these areas are less than a foot. In a typical year, the frost usually comes out of the ground by the end of March. .Lake and River Conditions... Ice thickness on rivers, streams and lakes ranges from open water to around 14 inches of ice at Deerfield. The cool nights and warm days will slowly deteriorate the ice over the next few weeks. .Weather Outlooks... Water temperatures in the tropical eastern Pacific Ocean are above average at the surface; however, subsurface water temperatures have trended to near average. This means El Niño Southern Oscillation (ENSO) neutral conditions are expected to develop by late spring. Historically, there is a tendency for La Niña to follow strong El Niño events. If this does occur, it will likely develop in the June- July time frame. This weather pattern typically favors drier conditions across northeastern Wyoming and western South Dakota through the summer. Temperatures are often a little cooler than average in the spring, but warmer than average in the summer. .Numerical River Outlooks... In Table 1 below, the current (CS) and historical (HS) or normal probabilities of exceeding minor...moderate...and major flood stage 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 greater 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: 3/16/2024 - 9/30/2024 : 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 -------- ----- ----- ----- : --- --- --- --- --- --- :Little Missouri River Camp Crook 12.0 17.0 19.0 : 9 41 <5 20 <5 6 :Moreau River Faith 16.0 18.0 21.0 : <5 21 <5 12 <5 6 :Belle Fourche River WY-SD State Line 15.0 16.0 18.0 : <5 16 <5 <5 <5 <5 :South Belle Fourche River Sturgis 15.0 17.0 19.0 : 20 26 11 18 7 9 :Belle Fourche River Elm Springs 19.0 22.0 24.0 : 9 16 <5 <5 <5 <5 :Cheyenne River Wasta 13.0 15.0 16.0 : <5 7 <5 <5 <5 <5 Plainview 17.0 19.0 20.0 : 27 44 16 27 12 17 :Bad River Midland 21.0 24.0 25.0 : 20 36 <5 5 <5 <5 :White River Kadoka 15.0 16.0 19.0 : 32 53 17 45 6 16 White River 14.0 15.0 17.0 : 26 47 24 36 18 22 Oacoma 15.0 20.0 25.0 : 41 66 12 23 <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: 3/16/2024 - 9/30/2024 Location 95% 90% 75% 50% 25% 10% 5% -------- ------ ------ ------ ------ ------ ------ ------ :Little Missouri River Camp Crook 1.9 1.9 1.9 3.0 6.1 11.9 13.4 :Moreau River Faith 1.9 3.0 4.7 6.7 8.9 11.2 12.5 :Belle Fourche River WY-SD State Line 4.4 4.4 4.4 4.5 7.1 10.9 12.7 :South Belle Fourche River Sturgis 3.5 3.6 4.9 7.6 12.4 17.1 19.5 :Belle Fourche River Elm Springs 4.8 4.9 6.1 9.5 14.5 18.3 21.0 :Cheyenne River Wasta 0.6 0.7 1.1 4.4 6.0 7.0 8.4 Plainview 8.8 8.8 10.5 13.7 17.5 20.5 21.0 :Bad River Midland 4.5 4.8 5.4 11.3 20.3 22.6 22.9 :White River Kadoka 6.3 7.2 9.2 13.1 15.3 17.8 21.5 White River 6.5 7.6 10.2 12.0 14.5 18.2 21.1 Oacoma 10.0 10.6 12.4 14.0 18.8 20.3 22.1 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: 3/16/2024 - 9/30/2024 LOCATION 95% 90% 75% 50% 25% 10% 5% -------- ------ ------ ------ ------ ------ ------ ------ :Little Missouri River Camp Crook 1.8 1.8 1.7 1.6 1.5 1.5 1.5 :Moreau River Faith 0.7 0.7 0.7 0.7 0.7 0.7 0.7 :Belle Fourche River WY-SD State Line 3.2 3.2 3.2 3.2 3.1 3.1 3.1 :South Belle Fourche River Sturgis 2.2 2.2 2.2 2.2 2.2 2.2 2.2 :Belle Fourche River Elm Springs 3.2 3.2 3.2 3.2 3.2 3.2 3.2 :Cheyenne River Wasta 0.5 0.5 0.4 0.3 0.3 0.3 0.2 Plainview 8.4 8.4 8.3 8.3 8.3 8.2 8.2 :Bad River Midland 2.9 2.9 2.7 2.7 2.7 2.7 2.7 :White River Kadoka 4.6 4.5 4.2 4.0 4.0 4.0 4.0 White River 4.3 4.2 4.1 4.0 3.9 3.9 3.9 Oacoma 8.4 8.3 8.1 8.0 7.9 7.8 7.8 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/unr for more weather and water information. .Outlook Schedule... This is the final spring flood and water resources outlook for the season. $$ Smith