Chicago weather: Timeline for severe storm threat, tornadoes possible

CHICAGO - Be weather ready! That is the message for the next two days as we have multiple rounds of strong to severe thunderstorms on the way.

First things first — we open with some fog near the lake and in Lake County, Illinois. That will quickly dissipate after the sun comes up this morning.

Tuesday's high of 88° is the hottest we’ve been this year. That distinction will last for about another 10 hours or so. Highs Wednesday will make it into the low 90s with enough humidity to make the heat index around 100°. That will be fuel to the fire for thunderstorms plowing through the area starting mid to late afternoon. Some of those storms could have destructive winds, which are the primary threat today. However, large hail and perhaps tornadoes are also on the table. A second wave of thunderstorms will arrive after dark and they too could be severe.

Thursday presents what could be an even greater threat for all severe thunderstorm hazards. It’s possible that late in the morning a few thunderstorms could be moving through our northern counties, but that’s not a guarantee. What is a near certainty is that intense thunderstorms will roll into our area late tomorrow. If there has been a recent trend among computer models, it is to delay the arrival of those thunderstorms by a couple of hours. What had looked like a mid to late afternoon start time now looks to be closer to 6 or 7 p.m. All hazards will be in play, including tornadoes, very large hail and destructive straight-line winds.

On top of all of that, the atmosphere is juiced to the point that rainfall totals could be impressive in many areas with the repeated rounds of storms. Once the storms end, perhaps around midnight or 1 a.m. Friday, the weather settles down for a couple of days.

What's next:

Friday and Saturday will feature plenty of sunshine with highs in the upper 70s on Friday and then warming into the mid 80s on Saturday. That night, a cold front will move through, sparking a few showers, followed by a real break from the heat and humidity for the next couple of days heading into early next week.

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