Following are details of the 2019 National Oceanic and Atmospheric Administration (NOAA) spring flood outlook. To no one's surprise, the Midwest and northern Plains river systems affected by flooding in the wake of the bomb cyclone storm March 12-13 are indicated to continue with notable flood risk for the rest of the season. Here are excerpts from the outlook. -- Bryce Anderson
This winter (2018-19) has brought above to much above normal precipitation to much of the United States. Several portions of the country received accumulated precipitation exceeding 200% of average to date. Heavy rainfall mid-February through mid-March brought flooding across much of the Mississippi River Basin and its tributaries. Heavy rainfall on snow in mid-March brought significant flooding -- including record flooding -- to the Lower Missouri River Basin. Additionally, accumulated snowpack has been higher than normal in the Upper Mississippi Valley, the Plains of the Missouri River Basin, Red River of the North, and the Great Lakes basins.
Basins with an increased risk of moderate to major flooding are as follows: the Upper, Middle, and Lower Mississippi River, lower Missouri, Red River of the North, Lower Ohio, Lower Cumberland, and Tennessee River basins. Additionally, an elevated risk of moderate flooding exists for basins in the Northeast as follows: the St. John, Penobscot, and Upper Hudson River basins.
Minor flooding is expected across much of the region east of the Mississippi River, as well as the Pacific Northwest, and Sierra Nevada basins. Minor to isolated moderate flooding is also projected for the central Idaho tributaries to the Snake River as follows: the Big Lost, Wood, Upper Boise, Payette, and Weiser River basins.
The spring flood outlook for the Mississippi River system is anticipated to create conditions conducive to hypoxia development and lead to an above average to large hypoxic zone in the northern Gulf of Mexico this summer. Nutrient loads from river discharge into the Chesapeake Bay are projected to produce an average hypoxia zone this summer.
Here are more details for the river systems of the central U.S.
UPPER MISSISSIPPI RIVER, MIDDLE MISSISSIPPI RIVER, AND THE RED RIVER OF THE NORTH BASINS
The potential for major flooding due to well above normal precipitation, snowmelt, saturated soils, and frozen ground is high compared to its historical average across the Upper Mississippi River and Red River of the North basins. Numerous break-up ice jams in the region have already caused significant flooding and will exacerbate flooding conditions throughout the spring season.
LOWER MISSISSIPPI RIVER BASIN AND ITS TRIBUTARIES
The tributaries of the Lower Mississippi River are currently experiencing minor to moderate flooding, whereas the mainstream Lower Mississippi River is currently experiencing major flooding. This is expected to continue for the foreseeable future as flood waters move downstream through the system. Impacts in these areas are being mitigated by local levee systems and the U.S. Army Corps of Engineers' operation of the Bonnet Carre Spillway, whose gates have been operated for the first time in two consecutive years.
In the state of Mississippi, minor to moderate flooding is projected in the Yazoo, Big Black, and Pearl River basins.
OHIO, CUMBERLAND, AND TENNESSEE RIVER VALLEYS
The Cumberland, Ohio, and Tennessee River basins in Kentucky and Tennessee received higher-than-normal precipitation this winter, leading to enhanced soil saturation levels. Rain is expected to be the main driver behind minor to moderate flooding in the region this spring.
In the Tennessee Valley, minor to moderate spring flooding is possible along the tributaries of the Tennessee River. Minor to moderate flooding is likely in the Cumberland, Green, and lower Kentucky River basins. In Indiana and Illinois, minor flooding is expected in the upper Wabash, Little Wabash, White, and Maumee River basins. In eastern Kentucky and eastern Tennessee, minor flooding is likely in the Licking and Big Sandy River basins. In Ohio, minor flooding is likely in the Maumee, Muskingum, Scioto, and Great Miami River basins. In West Virginia, minor flooding is expected in the Monongahela and Kanawha basins. Minor flooding is expected in the middle Ohio River.
It should be noted that although the probability of major flooding is lower than 50%, the Cumberland River Basin shows a 5-20% chance of major flooding this spring. Isolated major flooding is possible, especially in western and southern Kentucky and western Tennessee where soils are highly saturated.
MISSOURI RIVER BASIN
Overall, the spring flood risk is higher than normal for the lower Missouri River Basin, driven by above normal snowpack across the Plains, saturated soil conditions, and the presence of deeply frozen soils. Ice jam flooding has already been reported at many locations this winter.
Significant, record breaking flooding is already underway across the Lower Missouri River Basin. A storm system in the middle of March brought 2 to 4 inches of rain across the already saturated area. The combined effects of these rains and snowmelt also produced enhanced runoff. The Northern Plains have an above normal snowpack, and the flood risk is expected to stay relatively high for the region throughout the spring.
In eastern South Dakota, major flooding is expected to continue in the lower Big Sioux, Vermillion, Lewis and Clark Lake, and lower James Rivers. In Iowa, major flooding is expected in the Floyd, Ocheyedan, Rock, Little Sioux, and Big Sioux Rivers. In Nebraska, major flooding is expected in the Wood River, Shell Creek on the lower Platte, North Fork Elkhorn River, Logan Creek of the lower Elkhorn, lower Niobrara, portions of the Middle Platte, and Nishnabotna River basins. In the state of Missouri, major flooding is likely in the Tarkio, Nishnabotna, and Nodaway River basins. Also, the Platte River mainstem to the confluence of the Missouri River, as well as the Missouri River mainstem from Gavins Point Dam to Kansas City, have a risk of experiencing major flooding this spring.
In western South Dakota, moderate flooding is expected in the White, Grand, and Moreau River basins. In Nebraska, moderate flooding is expected in the upper Elkhorn and upper Platte River basins. In Kansas, moderate flooding is expected in the Smoky Hill, Saline, Solomon, Little Osage River basins. In Missouri, moderate flooding is likely in the Grand, Crooked, Blackwater, Lamine, and South Grand River basins.
In northeastern Montana, minor flooding is likely in the lower Milk River basin. In western and central North Dakota, minor flooding is likely in the Little Muddy Creek and Cannonball River basins. In western South Dakota, minor flooding is expected in the Little Missouri and Bad River basins. In Nebraska, minor flooding is likely in the Little Blue, Loup, and North Platte River basins. In Kansas, minor to moderate flooding is expected in the Big Blue, Little Blue, Marais des Cygnes, and the Republican River basins. In Missouri, minor to moderate flooding is likely in the Chariton, Moreau, Big Piney, Gasconade, Marmaton, Osage Rivers, as well as Petite Saline Creek.
Snowpack conditions over the Upper Missouri Basin above Fort Peck, Montana and Yellowstone Basin is near normal, though the snowpack in the St. Mary Basin was 85% of average, whereas the Milk River Basin was 150% of average. Streamflow conditions from snowmelt in the Upper Missouri and Yellowstone River basins this spring is forecast to be near normal.
The full report is at this link: https://bit.ly/…
Bryce Anderson can be reached at firstname.lastname@example.org
Follow him on Twitter @BAndersonDTN
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