Chicago weather forecast includes severe storms starting in afternoon, tornadoes possible

The Chicago weather forecast Tuesday includes the possibility of severe thunderstorms and even tornadoes, especially to the south, after several days of springlike warmth.

A Flood Watch is in effect for Cook, DuPage, Will, Grundy, Kane, Kankakee, Kendall, and La Salle counties in Illinois and Lake and Porter counties in Indiana until 3 a.m. Wednesday.

A surge of warm air into the Chicago area will set the stage for a potentially active stretch of weather late in the day, with temperatures climbing well over 70 in some spots, though a a backdoor cold from moving south off Lake Michigan could create a sharp temperature divide across Northern Illinois. 

However, the current conditions create the highest risk for tornadoes in the Chicago area since 2013, according to CBS News Chicago First Alert Meteorologist David Yeomans. As of 12:15 p.m., the very southern edge of Cook County, as well as counties to the south, the west and a large part of Northwest Indiana are now at a level 4 moderate severe storm threat, according to the Storm Prediction Center.

That divide could mean areas closer to the lake stay cooler, with clouds, drizzle and fog possible, while areas to the south remain warm and humid.

The primary window for severe weather is between 4 p.m. and midnight, with the greatest threat mainly south of Chicago, along and south of I-80. However, severe storms could crop up as early as 3 p.m.

What are the main severe weather threats Tuesday?

In areas along and south of I-80, storms could produce damaging winds, large hail and even a few tornadoes. Farther north, storms could still develop, but would be more likely to produce hail and gusty winds rather than tornadoes, due to the cooler and more stable air near the lake.

Heavy rain is also a concern, especially Tuesday night, as slow-moving storms could repeatedly move over some areas and potentially cause localized flooding and flash flooding.

The entire Chicago area is at a medium risk of tornadoes and flooding, a low to medium risk of wind damage, and a medium to high risk of large hail. Some hail could be as large as tennis balls. 

What is the tornado risk?

Areas along and south of I-80 and in Northwest Indiana are at a level four, or moderate, threat of severe storms Tuesday, and have the greatest risk to see tornadoes, though the entire area including the city have an enhanced chance of severe weather today. There is also a risk of long-tracked tornadoes. 

What is the difference between a tornado watch and a tornado warning?

A tornado watch means there are weather conditions that could lead to the formation of severe storms and tornadoes. If a tornado watch is issued for your area, the NWS advises you prepare for the event of a tornado warning, getting together supplies and determining where the safest place in your home is for you to take shelter.

A tornado warning means a tornado has been sighted or indicated by weather radar, and there is imminent danger to life and property. If a tornado warning is issued for your area, you should take shelter and safety precautions immediately. 

Tornado watches are typically issued for large areas that are potentially at risk, while tornado warnings are issued for much smaller areas, around the size of a city or a small county, that may be impacted by a tornado identified by radar or a trained tornado spotter.

What to do if there's a tornado warning

If a tornado warning is issued for your area, you should take shelter in the lowest level of your home or a basement if possible. If it's not possible to get to a basement, or you don't have one, take shelter in an interior room away from windows, like a bathroom, closet or hallway. If time allows, be sure you bring your pets with you.

If you are outside, seek shelter inside a sturdy building immediately; sheds, storage facilities and mobile homes are not considered safe by the National Weather Service.

If you're in your car, you should drive to the closest shelter immediately and take cover. If you can't get to a safe shelter, either get down in your car and cover your head or abandon your car and seek shelter in a low-lying area like a ditch or ravine, the NWS advises.

If you can, bring a flashlight, water, and your phone and charger into your safe room with you. If you have access to a radio, also bring the radio so you can stay informed of weather alerts, changes, and when the warning has been cleared.