There is the potential for widespread severe weather Wednesday evening in parts of the Midwest, including Chicago, Milwaukee and Minneapolis.
Widespread power outages and extensive tree damage is possible, especially in Wisconsin, where the severe risk level is at four out of five. The threat for a derecho -- long-lived, straight-line and damaging winds associated with rapidly moving thunderstorms -- is part of a larger severe weather outbreak that is expected to affect over 85 million Americans from the upper Midwest to the Northeast over the next two days.
While tornadoes garner a lot of attention because of their destructive ability, derechos can rival tornadoes in terms of destruction an impact. Derecho damage is typically "in one direction along a relatively straight swath," according to the National Weather Service.
Last year, a derecho caused major destruction in parts of Iowa and Illinois. The derecho had gusts up to 140 mph, spawned two tornadoes, killed four people and caused widespread damage and power outages. A "derecho of this intensity is a roughly once-in-a-decade occurrence" for the area, the NWS said.
Derechos are the most common in across the Southern Plains, as well as from the Mississippi Valley to Ohio, according to the NWS. For an event to be classified as a derecho, the NWS says that the swath of these damaging winds needs to more than 240 miles and have gusts of 58 mph or higher.
During most severe thunderstorms, there is a brief period of very gusty winds. A location that is hit by a derecho will see long-lived, extremely severe winds. The derecho itself may travel several hundred miles or more over the course of several hours. Because the period of peak wind gusts may last for an extended period, some have compared the destruction of a derecho to that of a hurricane.
Although these intense wind events can happen any time of the year, derechos are most likely to happen during the warmer months between May and August.
Derechos can bring other impacts besides wind damage. Sometimes, behind the initial burst of wind, training thunderstorms may form that could cause intense flash flooding.
Anytime there is a chance for severe weather, you should have a plan in place for how you will stay safe before, during and after the storm. If the NWS or media is saying a derecho is possible, you should prepare for communication interruptions and power outages. You should set aside emergency supplies and prepare as if you are about to be hit by a hurricane.