CHICAGO — The biggest severe weather threat so far this season is ahead for the Chicago area Saturday afternoon and evening.

Severe thunderstorms with possible tornadoes, large hail and damaging winds are expected to develop across northern Illinois into northwest Indiana this Saturday afternoon and evening. A deepening low pressure system will move through Iowa with storms forming along and ahead of first an advancing warm front from the south, followed by storms along and ahead of a cold front approaching from the west. A very strong 175 mph jet stream aloft will enhance upward motion and instability.

The headlined map prepared by the National Storm Prediction Center shows a rare Moderate to Enhanced area of severe storm potential enveloping the entire Chicago area Saturday with the prime time for severe development expected to be in the afternoon and evening hours.

The maps below show forecast probabilities of tornado, hail and damaging winds.

First map –  10 to 15 percent probability of a Tornado occurring within 25 miles of a given location in our area (yellow and red-shaded) with a 10 percent chance of an EF2-EF5 tornado (hatched area)

Second map – 15 percent probability of Damaging Winds in excess of 55 mph within 25 miles of a given point in our area (yellow-shaded)

Third map – 30 percent probability of Hail… 1–inch diameter or greater (red-shaded) and 10 percent probability of 2-inch diameter or greater (hatched red area) hail within 25 miles of a given point in our area

Updates at wgntv.com/weather.