Randomly cracked windshield

Is there any reason that my windshield would have randomly cracked while I was driving home the other day? Out of the blue a crack appeared which runs from the top dead center to the bottom of the windshield, in a perfectly straight line. Upon closer inspection I can't see any chips or damage that would have caused the crack and it's been above freezing lately, so I don't think that running my defrost caused it.

This is on a 2000 XJ, which is my 3rd Cherokee. My previous 1998 would sometimes make a random "popping" noise from the windshield area but I never had any cracks. Could this have been caused by some flex in the unibody or is it more likely a faulty windshield or bad installation, or a combination of some things? The previous owner had new glass installed a few months ago, just before I bought it.

I'm wondering if this is a common occurance or if there's something that I should have the glass shop look at when I have it replaced. For now I don't think I'll replace it until winter is over.

Happens all the time. Explanations vary, but contributors are sudden changes in temperature, deterioration of part, but not all, of the adhesive holding the windshield in, causing a change in local stress. It's very common for spots of rust to develop around the windshield mounting seam, and that will cause loosening and air leaks.

Although it seems a flimsy thing, glued-in windshields constitute a part of the overall roof structure, and they're affected by stress and flex.

I've had almost totally random luck with windshields. Some lasted nearly forever, others broke after a few months. Some grew slowly, some quickly. But I don't think I've had many vehicles that didn't need a new windshield at some point. My 99 has a huge growing crack that would fail inspection in just about any state but Vermont.

Most of my cracked windshields have occurred during winter, reinforcing the likelihood that sudden temperature changes contribute to the stress.

Every XJ I have ever had...

The windscreen cracks. Usualy in the Winter as the defrosters heat the inside of the glass faster than the heat can transfer to the ouside. Automotive Safety Glass is a sandwich construction of glass with a plastic separator between the layers. The plastic, besides doing it's primary job of holding the glass together in a crash, acts as an insulator.

The theory is that the placement of the defroster ducts apply heat in a localized area which causes the glass to expand in that area applying stress to the entire piece.

What I do know is that every one I have had has cracked, the crack starts in the more or less same place. This is why I carry Glass Replacement on my Insurance. About every three years, new glass... I don't even wait any more. I just tell the Insurance the glass is pitted due to the sand that blows around (which is true btw...) here and it is a safety action item. They are good with it.

So, unfortunately, glass is normal maintenance item on our Heeps.

Well, thanks for answers. I guess I got lucky with my past XJ's, a 1990 and 1998 which were both pitted but never cracked. I was just admiring how clear and un-pitted this one was when I noticed the crack appear!
Guess I'll wait until the spring to have it replaced and invest in some extra insurance for windshield.