AccuWeather map, 8/24/21.
SIOUX FALLS, S.D. (KELO.com) — AccuWeather meteorologists are concerned that some communities from the Dakotas and Nebraska to Iowa, Minnesota, Wisconsin and Illinois can be hit hard with dangerous and damaging storms and torrential rainfall through Friday.
“While a major outbreak of severe thunderstorms is not anticipated, the main threats from the thunderstorms will be from strong wind gusts that can reach as high as 80 mph and flash flooding in some cases,” AccuWeather Meteorologist Nicole LoBiondo said. A few incidents of large hail are possible as well.
The pattern will be set up by a bubble of strong high pressure with hot and humid air that is forecast to linger over Oklahoma into the end of the week, according to AccuWeather Senior Meteorologist Brett Anderson.
“Showers and thunderstorms will fire and repeat over the northern edge of this zone of high pressure close to the area where the jet stream will be,” Anderson explained.
Major cities at risk for flash flooding through midweek include Des Moines, Iowa; Sioux Falls, South Dakota; Minneapolis; Chicago and Milwaukee.
Mother Nature has demonstrated in recent days that a large outbreak of severe thunderstorms is not needed to pose a serious risk to lives and property, as evidenced by the shocking and tragic flash flood that unfolded in Waverly, Tennessee, on Saturday. The incident is an example of what can happen when complexes of drenching thunderstorms repeat over the same area for several hours, a meteorological effect known as “training.”
On Tuesday and Tuesday evening, the risk of severe storms with strong winds and torrential downpours may extend farther to the north and east and reach areas in north-central Minnesota, northern Wisconsin and part of northern and western Michigan.
This double whammy of severe thunderstorms and heavy rainfall may extend from central and eastern Nebraska to southern Minnesota, northern Iowa, northern Illinois and southern Wisconsin Tuesday. It is this overlap area that may be most prone to flooding at the local level.
This image shows 24-hour rainfall as of Tuesday morning over the north-central United States. A general 1-2 inches of rain fell, but there have been pockets of 2-4 inches of rain based on radar. (National Weather Service)
On Wednesday, severe thunderstorms are forecast from eastern Montana and the western part of the Dakotas to much of Nebraska. A separate area of heavy and gusty storms with the potential for localized severe weather may extend from Missouri to the Lower Peninsula of Michigan to Ohio, central Pennsylvania and western New York state. In both of these areas, there will be the potential for downpours capable of producing flash flooding.
High pressure over the southern Plains may break down and allow the pattern to break up a bit during the latter part of the week However, one pattern of showers and thunderstorms may hand off to another wet and thundery pattern from the northern Plains and parts of the Midwest.
Many locations from the Dakotas and Nebraska to northern Iowa and Minnesota are in need of rain with summer conditions ranging from abnormally dry to exceptional drought, according to data from the United States Drought Monitor. Since June 1, rainfall in much of this area generally ranges from 40-60% of average. While any non-flooding rainfall is welcomed, it may be too late to be of much value for this year’s growing season.
AccuWeather meteorologists urge residents to stay up to date when severe weather threatens their area and conditions can change rapidly. Motorists should never attempt to drive through flooded roads. Water can quickly cause vehicles to stall and float downstream, or the road may be washed out underneath the water.
Severe thunderstorms were rumbling through the eastern Dakotas early Tuesday morning. (AccuWeather)
Localized severe weather was reported at the beginning of the week, with one storm in Butte County, South Dakota, unleashing 80 mph wind gusts Monday evening. Later Monday night, a 91 mph wind gust was reported in Brown County, South Dakota.
There were at least three dozen reports of severe weather Monday. Most incidents were related to high winds, with a handful of reports of tornadoes and large hail.
( AccuWeather senior meteorologist, contributed this report.)
