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Midweek severe storm risk includes possible intense thunderstorm complex known as derecho

Anonymous • Jun 10, 2013 at 11:20 PM

AccuWeather.com reports complexes of strong, drenching and locally severe thunderstorms will reach from parts of South Dakota and Nebraska to Illinois, Ohio, western Pennsylvania and the Virginias during the middle of this week.

Part of this area could be hit by an intense thunderstorm complex, known as a derecho.

The pattern of thunderstorm complexes has the potential to bring localized incidents of flash flooding, damaging wind gusts, hail and frequent lightning strikes along a 1,000-mile swath spanning Tuesday, Wednesday and perhaps Thursday.

Travel delays caused by thunderstorms, poor visibility and flooded roadways are possible in some locations. There is a risk of downed trees, property damage and power outages and in a few neighborhoods.

The storms will affect areas on the Plains bound roughly by I-80 and I-90 Tuesday. During Wednesday, assuming the storms begin to turn to the right as they often do in these situations, the risk will shift to the Midwest and central Appalachians in areas approximately from I-64 to I-80.

Cities in the path of the storms include Sioux Falls, S.D., Des Moines, Iowa, Chicago, Indianapolis, Detroit, Cleveland, Cincinnati , Pittsburgh and Charleston, W.Va.

Some locations could be hit by more than one thunderstorm complex. In parts of the East, the storms will hit in the wake of Andrea's rainfall and additional storms early this week. In these areas the risk of flooding will be multiplied.

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 Nebraska to Missouri and 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.

When this happens in the presence of a strong jet stream, complexes of severe thunderstorms, known as mesoscale convective complexes (MCCs) or mesoscale convective systems (MCSs) can occur affecting multiple parts of multiple states.

The most intense, fastest-moving and longest-distance version of these is known as a derecho. These most severe thunderstorm complexes can bring wind 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. Derechoes evolve from thunderstorm complexes.

Depending on exactly where the parent complex of storms forms, the derecho could then track from the Midwest into part of the central Appalachians and the coastal mid-Atlantic 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.

More details on the thunderstorm complexes and potential derecho will be covered on AccuWeather.com by way of additional news stories, expert videos and forecasts this week.

EDITOR'S NOTE: This story was written by Alex Sosnowski, expert senior meteorologist for AccuWeather.com.

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