Tornado chances?

Question

what are the chances of a tornado coming to chicago?

Answer 1

Well, today, we almost had a tornado in Chicago.

The atmosphere was primed for a supercell event today in Chicago from 12 noon to about 4 pm today. The reason for this event ("supercell" is a thunderstorm with rotating updrafts) was that the atmosphere was very juiced...especially at the surface. Dewpoints were as high as 81 degrees F at 11:30 a.m., and very strong warm air advection from the south opened up Gulf moisture from south to north big time.

Also, storm-relative-helicities jumped to 240 meters squared per second squared (m2/s2), and convective available potential energies (or CAPEs) reached as high as 2200 joules per kilogram at the mean layer, and 3200 joules per kilogram at the surface.

The very high humidities caused severe atmospheric instability but the shear wind profiles were quite marginal for tornadoes. What it did to Chicago one hour ago was create noisy thunderstorms with winds as high as 40-50 mph, and rainfall rates as high as 3 inches per hour!

Those thunderstorms struck Chicago at 12:40 p.m. and lasted until 1:45 p.m.

Very strong upper vertical vorticities (UVVs) caused by strong updrafts from a nearby cold front from northwestern Illinois slamming into the already-destabilized atmosphere worsened the intensity of those thunderstorms, causing cloud-to-ground lightning rates to increase from 1 strike per minute to as much as 10 strikes per minute in 35 minutes time.

18,000 total lightning strikes struck the Chicago area, and as a result, 14,000 Chicagoans are now without power.

So, no tornadoes. But still, we got damage by flooding rains, and lightning hitting transformers and trees from non-tornadic thunderstorms.

The atmosphere is now stabilized right now, but Chicago paid a very heavy price still with non-tornadic, but very-efficient lightning-producing thunderstorms.

As for a chance of a tornado hitting Chicago....some of the major thunderstorms approaching Chicago...some that can be tornadic....sometimes steer away from the Chicago area known as "the Chicago Split"....especially if a cool lake breeze from Chicago's Lake Michigan sheers off the convective energy from the approaching storms.

Answer 2

Probably about the same as they are anywhere else, given some of the weird weather that has been happening lately.