Are winter tires necessary?  

I'm used to live in Missouri and we had some pretty bad winters there. I don't know if it's necessary to get snow tires. They make some pretty decent all-weather treads these days that might be worth the money. However, I'd suggest getting some chains to put on your tires. I don't know the technical term for them but they're just chains that fit around the outside of your tires and give you extra traction in the ice and snow. It's hard to tell what the winters will be like in Chicago. Mother Nature doesn't seem to be able to make up her mind! lol. It can be pretty treacherous to drive in snow. Actually it's more the ice that's the danger. Freezing rain can be pretty tricky. If I were you, I'd definitely invest in the chains. Probably cheaper than a set of tires and you can put them on and take them off pretty easily. How are you liking the Windy City thus far?

I'd recomend it. You ccan get all season tires that are ok, but I think specific winter tires are far better. Studded tires are even better if they aren't ilegal in Illinois. If you have never driven in snow before I would definately suggest winter tires. A few things to remember about winter driving....
Plan ahead, leave more time for your trip.
Try to anticipate sudden turns and having to stop a little longer in advance, defensive driving is essential in winter.
Drive a little slower but STEADY, use your breaks as little as you need to and when you do, apply them more slowly.
Make turns a little more gradualy.
Leave plenty of room between you and the car in front of you.
In a snowstorm, if you don't have to drive....don't.