Imagine parking under the shade of a huge tree thats been around for 40+ years only to have it fall on top of your car. 

This is what happened to me while visiting friends in the Dallas/Ft. Worth area.  There was no storm, no high winds, nothing that would normally make a limb break off of a tree.  But apparently extreme heat will make a tree limb give way as temperatures that day reached 107 degrees.  Moral of the story, sometimes the shade of a tree can cause more damage than your car being closed up and in the sun for several hours so watch out for those old trees.