There is a likelihood of severe thunderstorms featuring damaging winds, hail and flash flooding from South Dakota to Illinois, Pennsylvania and West Virginia through Wednesday night.
Part of this area could be hit by an intense thunderstorm complex, known as a derecho.
This particular pattern of thunderstorms has the potential to bring large complexes of thunderstorms spanning a 1,000-mile swath.
These complexes often bring incidents of 60-mph wind gusts, frequent lightning strikes and flash flooding on a local to regional basis. The pattern can also bring a handful of incidents of tornadoes and large hail.
Travel delays caused by thunderstorms, poor visibility and flooded roadways are likely in some locations. There is a risk of downed trees, property damage and power outages covering entire small communities and multiple neighborhoods of large cities.
The storms will affect areas in the Plains Tuesday night near I-80, expanding to the swath between I-74 and I-90. During the day Wednesday and Wednesday evening, assuming the storms begin to turn to the right as they often do in these situations, the risk will shift to parts of the Ohio Valley in areas approximately from I-64 to I-80.
Cities that could be in the path of the most violent storms through Tuesday night include Rapid City and Sioux Falls, S.D.; Rochester, Minn.; Des Moines, Iowa; Madison, Wis., Rockford, Ill. and perhaps as far east as Chicago.
As one or more complexes of the storms move along, cities that could be impacted Wednesday into Wednesday evening include Milwaukee, Wis., Chicago and Peoria, Ill.; Louisville, Ky., Indianapolis and Fort Wayne, Ind.; Columbus, Cleveland, Cincinnati, Pittsburgh and Morgantown and Charleston, W.Va.
Some locations could be hit by more than one thunderstorm complex, multiplying the risk of flooding.
Just southwest of the track of the thunderstorm complexes, there will be a higher risk for individual thunderstorms capable of producing tornadoes. This area could reach from portions of southern Nebraska to Missouri and western Kentucky and may include St. Louis.
The storms will be riding along the northern edge of a rim of heat building over the southern and central Plains this week.
Farther to the north, in cooler air, there is an elevated risk of of torrential rain and flooding problems.
When this happens in the presence of a strong jet stream, complexes of severe thunderstorms, known as mesoscale convective systems (MCSs) can occur affecting multiple parts of multiple states.
This graphic is an example of what an MCS looks like on a satellite photo and may not represent the size and position of the forecast weather this Tuesday night to Wednesday night.
The most intense, fastest-moving and longest-distance version of these is known as a derecho. These most severe thunderstorm complexes can bring gusts to 80 mph or more and damage to a large area, along a path covering hundreds of miles.
A derecho is challenging to predict, but there is a possibility of a derecho forming in the thunderstorm pattern this week. Derechos evolve from thunderstorm complexes.
Depending on exactly where the parent complex of storms forms, the derecho could then track from the northern Plains to the Ohio Valley given the steering winds and building heat to the south expected later this week.
The pattern of building heat over the West and southern High Plains, as well as complexes of thunderstorms riding southeastward over the Midwest and into part of the mid-Atlantic was discussed in AccuWeather.com's Summer 2013 Forecast.
AccuWeather.com meteorologists will continue to provide updates on the severe weather through new stories, expert videos and local forecasts as the thunderstorm complexes form, begin to move and likely intensify.
This story was first published Monday morning, June 10, 2013 and has been updated at midday Tuesday.
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