We saw an egg shaped craft surrounded by clouds, traveling very fast

We were traveling west on the road leading into our neighborhood. We were about to cross the bridge over the lake when I looked up and saw ominous clouds forming a thunderstorm and approaching rapidly. I looked up toward the sky and saw an egg-shaped craft, approximately 60 to 70 feet long, traveling at what I estimated 300 mph and 300 feet elevation. A soft silvery-white cloud surrounded the object, which appeared opaque as though you could see through it. It left a cloud trail that whisked away quickly. It was traveling from due north to due south and disappeared rapidly. I saw it very clearly and very precisely.