Ask the Meteorologist: How one storm produced a violent tornado, 6-inch hail in Illinois

One storm near Kankakee, Illinois, produced a large, destructive tornado Tuesday. It also produced what will likely go down as a record hailstone for the state. 

It looked like something out of a weather textbook. Let’s show you the moments we knew destruction was happening. 

The hail

We’ll start with the hail. 

I was getting ready for bed around 7 p.m. EDT Tuesday (since I’m up before 2 a.m.), and I checked my radar app. 

The image below is what I saw. 

A textbook supercell (rotating thunderstorm) was moving south of Chicago, but there was a unique feature that caught my attention. 

I’ve highlighted that in the image. It doesn’t look like much, but it’s a huge teller of large hail. It’s called a TBSS, or three body scatter spike. 

As the radar beam hits hailstones, it gets scattered three different times. That results in the appendage you see on radar extending off the storm.

Moments later, reports came in of hail that was baseball-sized and larger. One such report could break the state’s record for largest hailstone. 

The report suggested a hailstone of 6 inches in diameter.

According to NOAA’s National Centers for Environmental Information, this would break Illinois’ previous record for largest hailstone – and by a long shot.

The largest hailstone on record in the U.S. happened in South Dakota, and it was measured at 8 inches in diameter. 

Insane!

The tornado

While it takes time to assess the damage and come up with a rating, there was zero doubt that a tornado spawned from this storm too. 

It’s common during tornadoes for there to be hail on the northern flank of the storm. It’s called the “hail core,” and it is a result of rapidly rising air. 

In terms of the actual tornado, it became evident that one was active when looking at radar. 

A hook echo is commonly seen in supercell thunderstorms. It’s an indication of warm air flowing into the storm, while cold air flows down its rear flank. This is your rotational aspect of the storm that extends down to the surface.

The air spins rapidly and – eventually – it picks up debris. This can show up as a ball on the southern tip of the storm. 

Every bit of this storm was something out of a meteorology textbook – a marvel for those who admire the atmosphere, but a nightmare for those at ground level enduring its fury.