Hyperion's right, I had discounted the fact that a tornado powerful enough to carry something that big ten miles would probably just rip the plane up first. Still, the possibility of a tornado picking a fully-loaded tanker truck up off Wacker Drive and hurling it into the side of the Sears Tower IS plausible and very scary.
if you want to be over the top on the where's-my-antidepressant scale, make it a Greyhound or a school bus, from the perspective of a horrified citizen inside the building, seeing the faces of the passengers through the vehicle windows