SPRING FLOOD OUTLOOK NATIONAL WEATHER SERVICE MISSOURI BASIN RIVER FORECAST CENTER PLEASANT HILL, MO MARCH 08, 2023 NARRATIVE PART 1 OF 1 ATTN WFO'S SERVED BY MBRFC. This Spring Flood Outlook is not for public release until Thursday, 09 March 2023. This Spring Outlook is for the Missouri River drainage which includes rivers in Montana, Wyoming, Colorado, North and South Dakota, Nebraska, Kansas, Iowa, Minnesota, and Missouri. SPRING FLOOD OUTLOOK Flood risk this Spring within the Missouri River basin varies, with much of the basin having a reduced flood risk due to the ongoing drought. However, as a result of a near-to-above average mountain snowpack, and a significant plains snowpack, there also exists pockets of the basin having a near normal to even enhanced flood risk for Spring 2023. To provide context, a normal risk indicates that a location that typically experiences Spring time flooding is likely to see flooding again this year. However, a normal risk for flooding does not necessarily mean that a location is expected to flood. For those locations which do not typically experience flooding, a normal risk simply indicates that flooding is again not expected this year. By the same token, a reduced risk of flooding does not necessarily mean that flooding is not expected. On the other hand, an enhanced risk does not necessarily indicate flooding is likely. The Missouri River basin is in its third year of continuous drought. The time period covered by Water Years 2020, 2021, and 2022, extending from October 2019 through September 2022, was the 10th driest 3-year period in 125 years of record keeping for the basin. To provide context, the Dust Bowl years of the 1930s had 3-year stints that ranked as the 1st, 2nd, 4th, 5th, and 6th driest 3-year periods on record. The latest Drought Monitor, released 02 March 2023, categorizes 56 percent of the Missouri River basin in drought. Mountain snowpack overall is generally near average. The exception being the North Platte River basin, where an above average snowpack exists thus far this year. Minor flooding along the North Platte River in Wyoming is anticipated. Water supply forecasts issued in early February by the National Weather Service project generally lower than average April-September runoff volumes for the mountainous west. Again, the one exception being the North Platte basin, which is expected to produce an above average runoff volume in 2023. More information regarding current Water Supply Forecasts can be accessed at weather.gov/mbrfc/water An appreciable plains snowpack exists over the Milk River basin, across much of North Dakota and the eastern half of South Dakota, and in extreme northwest Iowa. The plains snowpack, where it exists, is thought to have precluded the development of a deeply frozen ground condition. Where plains snowpack is absent, the ground has either now thawed, or if frost still exists, is thought to remain fairly porous due to the ongoing drought conditions. In other words, while the ground may still be cold, the general absence of soil moisture to lock into place should allow for some infiltration of future rain events and/or snowmelt. Therefore, frozen ground is not expected to exacerbate flood risk for the Missouri River basin this Spring. Despite below normal streamflows this Fall and Winter, river ice action has already presented some challenges within the Missouri River basin this winter. River ice has resulted in elevated river stages along the Gallatin River in Montana, the South Fork Shoshone River in Wyoming, and along the lower reach of the North Platte River in Nebraska. Thus far, impacts from these western area freeze-up ice jams have been minor and localized. The bitter cold snap which draped the basin in mid-to-late December also resulted in ice jams along the lower Missouri River, one jam in the Nebraska-Iowa reach of the river, and a separate one in the reach downstream of Kansas City. Neither jam resulted in flooding, but both jams resulted in record low stages in the stretches of the river below each of the respective jams. Going forward, it is thought that the Missouri River basin has a low risk for ice jam break-up flooding this season. However, as long as there is ice in the rivers, and a snowpack on the ground, the risk is nevertheless present. Please note, the probabilistic quantifications that form the basis for this Spring Flood Outlook do not take into account the presence of river ice. Springtime flooding in the lower one-third of the basin, including southern Iowa, eastern Kansas, and the state of Missouri, is driven by typical thunderstorm activity. Minor flooding has already occurred along some of the tributaries in the state of Missouri this calendar year, and episodic flooding is likely to continue through this Spring in this region of the basin. The following state by state flood potential discussions are based on long-range probabilistic river outlooks developed this week. Again, it must be stressed, these outlooks do not take into account the presence of river ice. In Wyoming, minor flooding is likely along the North Platte River. In North Dakota, minor flooding is expected along the Cannonball River and along Apple Creek. The James River and Beaver Creek are also being watched closely. In South Dakota, moderate flooding is expected along the James River and in the upper reach of the Big Sioux River. Snake Creek may also experience moderate level flooding. Minor flooding is likely along the Vermillion and White Rivers, and Turtle Creek is also projected to have minor flooding. In Iowa, minor flooding is likely along the Nishnabotna River, along the upper reach of the Little Sioux River, and on the lower end of the Big Sioux River. . In Kansas, Stranger Creek will experience moderate level flooding, while the Marais des Cygnes and Little Osage Rivers are likely to have minor flooding. In the state of Missouri, moderate flooding is likely along the Grand, Crooked, Blackwater, Moreau, South Grand, and Tarkio Rivers. Moderate level flooding is also expected along Wakenda and Big Creeks. Minor flooding is projected for the Chariton, Lamine, Big Piney, Gasconade, Little Osage, Marmaton, Sac, and Platte Rivers. Minor flooding is also expected along Moniteau. Roubidoux, and Petite Saline Creeks. The Missouri River from Nebraska City to the mouth could also see episodic minor flooding this Spring. These projections of river stages are based on current observed states of streamflow, soil moisture, and snowpack, coupled with future precipitation and temperature patterns and anticipated operational hydrologic changes such as reservoir releases and canal diversions. "Outlooks" are provided for long-range (weeks to months) projections based on climatological patterns of precipitation and temperature. "Forecasts" are provided for short-term (days) projections based on forecast patterns of precipitation and temperature. The uncertainty of these products varies from season to season and location to location. The uncertainty of forecasts tend be less than the uncertainty of outlooks due to their shorter lead time. Users of these products are encouraged to contact their nearest National Weather Service Forecast Office for continued updates of meteorological conditions which can have significant impacts on flood preparedness planning and flood fighting activities. For additional quantitative information please refer to AHPS products for probabilistic outlooks of potential flooding. Refer to short-term flood forecasts and products, if any are currently issued, for information about ongoing or near-term anticipated flooding. This is the last scheduled Spring Outlook of the season. Should significant changes occur subsequent to this Outlook, additional Outlooks can be released to update expected conditions. Additional river information, including the monthly Water Supply Outlook, can be accessed at the following URL: http://weather.gov/mbrfc Current Snow Conditions The conditions listed below are based on observations and model data as of Wednesday morning, March 8th. Montana Plains Snow depths of 3 to 11 inches are being reported across the plains of the Milk basin in northern Montana with water equivalents in the 2.0-4.5 inch range. Elsewhere across eastern Montana, snow depths are generally less than 3 inches with water equivalents less than 1.0 inch. Wyoming and Colorado Plains Snow depths of generally less than 3 inches are being reported across the plains of Wyoming and Colorado with water equivalents less than 0.5 inches. Mountainous West Snowpack conditions in the mountainous areas of the basin are generally near normal. In Montana, the Jefferson, Musselshell, Missouri headwaters, Sun, Teton, and Marais River basins are reporting a near normal snowpack (90-110%). The St. Mary and Milk basins are reporting a near normal snowpack (88%). In Wyoming, the Tongue, Bighorn, Powder, Wind, and Yellowstone River basins are reporting a near to above normal snowpack (100-115%). The higher elevations of the North Platte River basin are reporting an above normal snowpack (125%). In Colorado, the higher elevations of the South Platte River basin are reporting a near normal snowpack (103%). North Dakota Snow depths of 15 to 20 inches are being reported across much of North Dakota with water equivalents in the 2.0-7.0 inch range. Lower snow depths of generally less than 6 inches are being reported across extreme western North Dakota with water equivalents less than 2.0 inches. South Dakota The Black Hills in South Dakota have 10 to 36 inches of snow depth with water equivalents in the 3.0-9.0 inch range. Snow depths of 8 to 24 inches with water equivalents generally in the 2.0-5.0 inch range are being reported across the eastern half of the state. Lower snow depths of generally less than 6 inches are being reported across the western half of South Dakota with water equivalents generally less than 2.0 inches. Iowa Snow depths of 5 to 15 inches are being reported across the northwestern corner of Iowa with water equivalents in the 2.0-4.0 inch range. Little to no snow is being reported across southwestern Iowa. Nebraska Snow depths of 1 to 5 inches are being reported across extreme northern Nebraska with water equivalents generally less than 1.0 inch. Elsewhere across the state, little to no snow is being reported. Kansas No snow is being reported across Kansas. Missouri No snow is being reported across Missouri. Current Soil Moisture Conditions The US Drought Monitor indicates that much of the Missouri River basin is experiencing below normal soil moisture conditions. Extreme to exceptional drought is indicated across much of Nebraska and the western half of Kansas. Severe to extreme drought is indicated across northern Montana, eastern Wyoming, eastern Colorado, and northwestern Iowa. Abnormally dry to moderate drought is indicated across much of the remainder of the Missouri River basin. The exception is across northeastern Kansas and most of Missouri where normal to above normal soil moisture is indicated. Isolated frost depth reports suggest that soils across Montana, Wyoming, South Dakota, and North Dakota have frost penetration ranging from 0.5 to 3 feet. Frost depths of less than 0.5 feet are being reported across Nebraska, Iowa, Colorado, Kansas, and Missouri. Current River Conditions A large majority of rivers across the northern half of the Missouri River basin are iced over. Generally, river levels across the basin are currently running near to below normal, or estimated to be so if the rivers are frozen. Rivers across southern Missouri are running above normal due to recent rainfall. A summary of river flow conditions at selected river stations for March 8th follows: Long Term Current Mean (CFS) (CFS) James River - Huron, SD 204 67 (EST) Big Sioux River - Akron, IA 825 800 (EST) Platte River - Louisville, NE 8140 8500 Kansas River - Desoto, KS 3460 3120 Gasconade River - Jerome, MO 2360 7310 Missouri River - Omaha, NE 17900 19600 Missouri River - Rulo, NE 29800 31500 Missouri River - St. Joseph, MO 36100 30200 Missouri River - Waverly, MO 42300 38000 Missouri River - Hermann, MO 68900 97200
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