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Spring Flood Outlook |
Probabilistic Hydrologic Outlook National Weather Service ST. LOUIS MO 230 PM CST THU FEB 25 2021 ...Spring Flood and Water Resources Outlook Number 2... ...Minor flooding likely along the Mississippi, Missouri, and Illinois Rivers... ...Most local streams have a near normal flood risk this spring... This outlook uses the term St. Louis Service Area to refer to the Mississippi River from above Canton Missouri to above Cape Girardeau Missouri, the Missouri River above Jefferson City Missouri to its confluence with the Mississippi River, the Illinois River downstream from its confluence with the LaMoine River to its confluence with the Mississippi River, and for tributary rivers in eastern Missouri, and west central and southwest Illinois. There is no ongoing flooding anywhere within the St. Louis Service Area, so probabilities within this outlook are not skewed by any ongoing flooding. This outlook is based on current streamflows and soil moisture over the area, and upstream snowpack, particularly in the Mississippi, Missouri, and Illinois river basins. The statistics are based on about 30 to 60 years of historical rainfall and stream crests. More than normal rainfall could cause higher-than-expected crests at individual forecast locations, while less than normal rainfall could keep streams from reaching "likely" crests. The Mississippi and Missouri rivers are experiencing near normal streamflow for this time of year, while flows along the Illinois River have experienced well below normal streamflow through most of the past winter. This is providing a low to mostly average starting point for these rivers to accept future runoff. Soils have dried out considerably across the Midwest since last summer, leaving local areas with near to below normal soil moisture. Drier soils are the rule from Minnesota and the Dakotas through western Kansas. This will provide the upper Mississippi River and middle Missouri River basins with additional storage, which acts as a deterrent to flooding. Finally, snowpack and snow water equivalent in this snowpack are well below average from northern Wisconsin, most of Minnesota, and the Dakotas. In fact, the Plains states north through the Dakotas are essentially snow-free, except for a small area over southeastern Nebraska. However, this snow water equivalent is well above average from southern Nebraska through much of Iowa, northern Illinois, and southern Wisconsin. Due to close proximity of this above normal snowpack, look for a likelihood of minor flooding for the Illinois, Missouri, and Mississippi rivers. However, given the below normal snowpack in other portions of these basins, the likelihood of significant (moderate or greater) flooding is not as great, and in many locations the threat of significant flooding is well below historical averages for the spring months. For local basins, the chances for flooding at most locations throughout the St. Louis service area are near or above average. Minor flooding is likely along the Fabius rivers, the Middle Fork Salt River, the Cuivre River, the Meramec River, the Bourbeuse River, the Big River, the Moreau River, and the Kaskaskia River. Soil moisture and wintertime precipitation have left these areas with moist soils, but not much different from normal. Most local forecast points have minor flood probabilities close to or slightly above normal, while these locations have near normal probabilites for significant flooding. In the near term, the Climate Prediction Center calls for above normal temperatures throughout the bi-state region and near normal precipitation chances in the 6 to 10 day outlook. By days 8 through 14, temperatures should remain above normal, while there`s a slightly better than average chance of above normal precipitation. For the month of March, there`s a slightly better than average chance of warmer than normal temperatures across the bi-state region. March precipitation should be close to normal over eastern Missouri while Illinois has a better than average chance of above normal precipitation. Looking ahead to the next 3 months of March through May, temperatures are expected to be above normal throughout the St. Louis service area, while precipitation chances will be very similar to March: near normal chances for typical precipitation amounts for the spring months in Missouri and better chances for above normal precipitation across Illinois. 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: 03/01/2021 - 05/30/2021 : 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 -------- ----- ----- ----- : --- --- --- --- --- --- :Mississippi River Canton 15.0 20.0 25.0 : 70 63 16 16 <5 <5 LaGrange 17.0 23.0 25.0 : 52 52 9 10 <5 <5 Quincy 19.0 22.0 26.0 : 56 56 24 27 9 10 Lock & Dam 21 18.0 21.0 25.0 : 55 53 24 26 9 10 Hannibal 17.0 22.0 24.0 : 69 61 15 15 9 10 Saverton 16.0 20.0 24.0 : 73 64 31 38 10 11 Louisiana 15.0 20.0 25.0 : 84 71 28 33 6 8 Clarksville 25.0 31.0 33.0 : 84 72 26 28 14 14 Winfield 26.0 30.0 34.0 : 79 65 37 40 9 10 Grafton 20.0 24.0 29.0 : 68 72 28 36 7 6 Mel Price LD 21.0 29.0 34.0 : 72 73 24 40 <5 6 St. Louis 30.0 35.0 40.0 : 56 66 27 47 7 11 Chester 27.0 35.0 40.0 : 81 79 39 57 17 27 :North Fabius River Ewing 11.0 17.0 20.0 : 63 54 15 15 10 10 :Middle Fabius River Ewing 12.0 17.0 20.0 : 56 50 14 14 8 8 :South Fabius River Taylor 10.0 14.0 19.0 : 52 52 17 17 <5 <5 :North River Palmyra 13.0 16.0 22.0 : 24 27 11 11 <5 <5 :Mid Fork Salt River Holliday 17.0 22.0 26.0 : 51 51 6 5 <5 <5 :Salt River New London 19.0 25.0 27.0 : <5 <5 <5 <5 <5 <5 :Cuivre River Troy 21.0 25.0 29.0 : 51 51 24 24 7 7 Old Monroe 24.0 27.0 30.0 : 55 61 28 25 14 14 :Dardenne Creek St. Peters 18.0 20.0 23.0 : 30 30 17 16 <5 <5 :Meramec River Steelville 12.0 20.0 25.0 : 48 41 <5 <5 <5 <5 Sullivan 11.0 20.0 29.0 : 71 67 15 12 <5 <5 :Bourbeuse River Union 15.0 22.0 26.0 : 52 51 11 11 <5 <5 :Meramec River Pacific 15.0 23.0 27.0 : 44 43 7 7 <5 <5 :Big River Byrnesville 16.0 20.0 28.0 : 55 49 24 22 <5 <5 :Meramec River Eureka 19.0 26.0 31.0 : 46 44 18 17 7 7 Valley Park 18.0 21.0 27.0 : 46 50 37 42 18 19 Fenton 23.0 29.0 32.0 : 47 56 16 20 10 12 Arnold 24.0 35.0 38.0 : 81 76 25 30 17 24 :Kaskaskia River Vandalia 18.0 24.0 26.0 : 74 82 34 35 17 19 Carlyle TW 423.5 431.0 435.0 : 23 43 <5 <5 <5 <5 :La Moine River Ripley 22.0 23.0 27.0 : 42 41 33 35 11 12 :Moreau River Jefferson City 17.0 25.0 29.0 : 79 87 40 40 17 15 :Maries River Westphalia 10.0 15.0 20.0 : 42 52 18 19 <5 <5 :Gasconade River Rich Fountain 20.0 25.0 30.0 : 34 34 24 26 5 6 :Missouri River Jefferson City 23.0 25.0 30.0 : 43 60 31 53 14 17 :Osage River St. Thomas 23.0 30.0 35.0 : 14 16 <5 <5 <5 <5 Mari-Osa Campgrou 19.0 22.0 25.0 : 36 64 17 27 8 13 :Missouri River Chamois 17.0 28.0 31.0 : 71 77 11 11 6 6 Hermann 21.0 26.0 33.0 : 76 81 33 57 12 13 Washington 20.0 28.0 31.0 : 57 69 13 16 9 10 St. Charles 25.0 30.0 36.0 : 64 71 23 33 8 9 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: 03/01/2021 - 05/30/2021 Location 95% 90% 75% 50% 25% 10% 5% -------- ------ ------ ------ ------ ------ ------ ------ :Mississippi River Canton 10.9 11.9 14.3 16.3 18.3 21.7 23.0 LaGrange 11.8 12.8 15.2 17.2 19.2 22.6 23.9 Quincy 14.2 14.9 17.4 19.4 21.8 25.6 27.6 Lock & Dam 21 12.3 13.2 16.2 18.2 20.5 24.6 26.9 Hannibal 13.8 14.6 16.2 18.4 20.4 23.6 26.5 Saverton 12.0 13.2 15.8 18.4 20.9 24.1 26.5 Louisiana 12.7 13.7 15.9 18.3 20.5 23.1 25.3 Clarksville 22.0 23.4 26.0 28.9 31.1 33.7 35.5 Winfield 22.2 23.6 26.2 29.0 31.1 33.5 35.6 Grafton 16.1 16.6 18.3 21.7 24.6 28.4 29.7 Mel Price LD 15.4 17.1 20.9 24.2 28.7 31.2 33.5 St. Louis 17.9 21.4 26.6 30.8 35.9 39.1 41.3 Chester 20.0 24.4 29.1 32.8 37.6 42.3 44.1 :North Fabius River Ewing 6.8 7.2 9.5 12.3 14.7 19.9 21.4 :Middle Fabius River Ewing 5.8 6.8 9.1 12.6 15.3 19.2 21.8 :South Fabius River Taylor 5.6 6.5 8.0 10.1 13.2 16.4 18.3 :North River Palmyra 6.3 6.9 8.7 10.4 12.9 16.5 18.1 :Mid Fork Salt River Holliday 10.6 11.3 14.6 17.1 18.3 20.8 22.0 :Salt River New London 5.7 7.4 9.2 9.9 11.2 13.1 13.4 :Cuivre River Troy 12.0 13.2 16.8 21.6 24.9 27.1 29.7 Old Monroe 17.6 20.1 22.0 24.5 27.6 30.6 31.3 :Dardenne Creek St. Peters 8.4 9.5 11.9 15.2 19.1 20.6 22.0 :Meramec River Steelville 3.8 5.7 8.1 11.7 14.4 16.2 19.9 Sullivan 7.5 7.9 10.2 14.4 18.4 21.6 26.3 :Bourbeuse River Union 8.9 10.5 11.8 15.2 18.7 22.9 25.4 :Meramec River Pacific 7.3 7.7 11.4 14.8 18.6 22.3 26.3 :Big River Byrnesville 8.5 9.9 12.2 16.6 19.7 22.9 25.7 :Meramec River Eureka 10.2 10.7 14.4 17.8 23.6 29.3 35.6 Valley Park 8.2 9.3 13.4 17.2 25.5 31.8 36.6 Fenton 14.0 16.2 19.7 22.4 27.4 32.1 36.1 Arnold 18.7 19.9 25.8 29.5 34.8 39.0 41.2 :Kaskaskia River Vandalia 12.8 14.0 17.2 22.6 25.3 27.1 28.7 Carlyle TW 415.9 416.5 418.3 420.2 423.4 424.0 424.7 :La Moine River Ripley 10.9 12.4 16.3 19.8 24.7 27.4 28.3 :Moreau River Jefferson City 9.5 13.7 17.6 22.0 27.2 33.6 40.1 :Maries River Westphalia 2.5 3.6 5.0 8.4 13.2 16.5 18.4 :Gasconade River Rich Fountain 5.5 8.3 10.5 16.0 24.1 28.4 31.0 :Missouri River Jefferson City 11.1 14.8 19.0 21.7 25.6 33.1 36.0 :Osage River St. Thomas 7.9 8.7 11.9 13.4 16.6 24.9 27.1 Mari-Osa Campgrou 10.5 11.7 15.0 17.6 19.6 24.7 29.0 :Missouri River Chamois 9.2 12.3 16.7 19.1 22.5 28.3 31.2 Hermann 14.1 18.3 21.1 24.5 27.2 34.3 36.0 Washington 10.6 14.3 17.1 20.8 23.6 30.6 34.5 St. Charles 17.9 21.1 23.4 26.7 29.1 35.4 37.4 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: 03/01/2021 - 05/30/2021 Location 95% 90% 75% 50% 25% 10% 5% -------- ------ ------ ------ ------ ------ ------ ------ :Mississippi River Canton 4.7 4.6 4.4 4.2 4.0 3.5 3.1 LaGrange 5.6 5.5 5.3 5.0 4.8 4.4 4.0 Quincy 11.8 11.8 11.7 11.6 11.5 11.2 11.0 Lock & Dam 21 5.3 5.2 5.0 4.7 4.5 4.1 3.7 Hannibal 10.4 10.4 10.2 10.1 10.0 9.9 9.8 Saverton 6.2 6.1 5.9 5.6 5.3 4.9 4.7 Louisiana 12.0 12.0 11.9 11.9 11.9 11.9 11.9 Clarksville 16.5 16.4 16.1 15.7 15.3 14.7 14.2 Winfield 16.3 16.2 15.9 15.6 15.0 14.5 14.1 Grafton 15.2 15.2 15.2 15.1 15.0 14.8 14.7 Mel Price LD 7.7 7.5 7.3 6.8 6.1 5.1 4.5 St. Louis 7.1 7.0 6.6 5.6 4.4 3.2 1.7 Chester 10.9 10.7 10.3 9.3 7.9 6.6 4.9 :North Fabius River Ewing 3.8 3.7 3.5 3.4 3.2 3.1 3.0 :Middle Fabius River Ewing 3.3 3.2 3.1 3.0 2.9 2.8 2.8 :South Fabius River Taylor 2.3 2.2 2.0 2.0 1.8 1.7 1.6 :North River Palmyra 4.5 4.5 4.5 4.3 4.2 4.1 3.8 :Mid Fork Salt River Holliday 3.9 3.9 3.9 3.9 3.9 3.8 3.7 :Salt River New London 6.2 5.1 4.8 3.9 2.4 2.1 2.1 :Cuivre River Troy 6.3 6.2 5.9 5.6 5.4 5.3 5.2 Old Monroe 12.5 12.3 12.0 11.5 10.8 10.2 9.8 :Dardenne Creek St. Peters 1.7 1.7 1.4 1.3 1.2 1.1 1.1 :Meramec River Steelville 2.1 2.0 1.8 1.6 1.5 1.4 1.3 Sullivan 3.3 3.2 2.9 2.7 2.6 2.4 2.3 :Bourbeuse River Union 2.7 2.6 2.5 2.4 2.3 2.1 2.0 :Big River Byrnesville 3.6 3.3 2.9 2.5 2.1 2.0 1.8 :Meramec River Eureka 4.4 4.3 4.0 3.7 3.5 3.3 3.2 Fenton 4.5 4.2 3.6 2.7 2.1 1.7 1.5 Arnold 8.2 8.1 7.9 7.5 7.2 6.7 6.6 :Kaskaskia River Vandalia 6.7 5.3 3.5 3.1 2.9 2.7 2.6 Carlyle TW 415.7 415.6 413.3 411.2 411.2 411.2 411.2 :La Moine River Ripley 5.9 5.8 5.5 5.2 4.9 4.7 4.5 :Moreau River Jefferson City 2.2 2.1 2.1 2.0 1.9 1.8 1.8 :Maries River Westphalia 1.9 1.8 1.6 1.4 1.3 1.1 1.1 :Gasconade River Rich Fountain 4.2 4.2 3.9 3.7 3.3 3.1 3.0 :Missouri River Jefferson City 5.7 5.4 5.1 5.0 4.4 3.9 3.7 :Osage River St. Thomas 3.2 3.2 2.8 2.5 2.5 2.1 1.5 :Missouri River Hermann 6.6 5.9 5.6 5.5 5.5 5.3 4.8 Washington 3.5 2.9 2.6 2.4 2.4 2.2 1.6 St. Charles 10.4 9.7 9.4 9.3 9.2 9.0 8.4 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/lsx for more weather and water information. The next outlook update will be issued in two weeks, on Thursday, March 11th. $$ Fuchs |