On this day in 2013, an unordinary late season tornado outbreak occurred across Illinois, Indiana, Michigan, Kentucky and Ohio. This particular tornado outbreak was the deadliest and costliest in Illinois to occur in the month of November and the fourth largest in recorded Illinois state history. This event resulted in 73 tornadoes, with reports of over 100 injuries and 11 fatalities.
Forecasts for the development of this event had been well anticipated, with initial forecasts led by the NOAA Storm Prediction Center five days in advanced. These storms were associated with a strong trough in the upper levels of the atmosphere, as well as having forecasts of a potent mid-level jet moving across the Mississippi River valley. The pressure gradient force, or in other words the force which results when there is a difference in pressure across a surface, tends to bring stronger winds in November compared to the summer or spring months. This leads to greater wind shear. The morning of the outbreak showed there was a particularly strong vertical wind shear, providing the perfect setup for long-tracked tornadoes to occur.
Two of the tornadoes, both in Illinois, were rated EF4 on the Enhanced Fujita Scale. These were the strongest documented tornadoes during the outbreak resulting in five deaths. In addition to tornadoes the system also produced baseball sized 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 separate locations. There were also seven tornadoes rated EF3, 23 tornadoes rated EF2, 28 tornadoes rated EF1 and 13 tornadoes rated EF0.
Tornadic events, especially of this magnitude, are an uncommon occurrence in the month of November. Normally in late autumn and into winter there is not sufficient warmth and moisture for thunderstorm development. However, in this case, a low pressure system across the plains had pushed tropical warmth and moisture northward from the Gulf of Mexico for nearly two days. This moisture was akin to that typically observed during summertime, given dew point temperatures in the mid to upper 60’s. Combine this with air temperatures of around 70° F (21° C) and these combined factors aided in the generation of instability to get thunderstorms to form. The warmth combined with the high wind shear was the perfect setup for these supercell storms to develop. This is just a reminder that people should stay vigilant throughout the entire year because tornadoes can happen at pretty much any time especially throughout the midwestern portion of the United States.
To learn more about other past historic weather events from around the world, be sure to click here!
© 2018 Weather Forecaster Michael Ames