The November 17, 2013 tornado outbreak was the deadliest and costliest in the U.S. state of Illinois to occur in the month of November and fourth largest for the state overall. Associated with a strong trough in the upper levels of the atmosphere, the event resulted in 73 tornadoes tracking across regions of the Midwest United States and Ohio River Valley, impacting seven states. Severe weather during the tornado outbreak caused over 100 injuries and eleven fatalities, of which eight were tornado related. Two tornadoes—both in Illinois and rated EF4 on the Enhanced Fujita Scale—were the strongest documented during the outbreak and combined for five deaths. In addition to tornadoes, the system associated with the outbreak produced sizeable hail peaking at 4.00 in (10.2 cm) in diameter in Bloomington, Illinois, as well as damaging winds estimated as strong as 100 mph (160 km/h) in three locations.
The development and progression of a severe weather event on November 17 had been well anticipated, and appeared in Storm Prediction Center products as early as November 12. The first storms associated with the event formed during the afternoon and evening hours of November 16 over the Great Plains, producing primarily hail and strong winds. However, tornadic activity was limited to November 17, as individual supercell thunderstorms tracked across the Midwest United States, at times producing long-tracked tornadoes. The first tornadoes formed over Illinois, while the final tornadoes developed over Tennessee. Towards the end of November 17, these individual systems had merged into an extensive squall line that tracked eastward across the Mid-Atlantic states, producing damaging wind before exiting into the Atlantic Ocean early on November 18.
With damage estimated at approximately $1.6 billion, the tornado outbreak became the seventh weather event and fifth tornado outbreak in the U.S. to accrue over $1 billion in damage that year. Tornadoes alone were responsible for $1.067 billion in damage, with the EF4 tornado that struck Washington, Illinois accounting for $935 million of the total. In addition to structural damage, widespread power outages affected thousands of electricity customers across the same regions impacted by the tornado outbreak and subsequent squall line. Non-tornadic deaths and injured include one killed in Jackson County, Michigan, when a tree fell on a car, one killed by live wires in Shiawassee County, Michigan, one killed after touching a downed wire in Detroit, and two minor injuries in a home damaged by wind in Ohio.