3 slow moving disks over south Boulder

My husband and I had just parked at a restaurant near the intersection of 28th Street and the Diagonal in Boulder, Colorado.  We both saw three silvery-white disks in a triangular formation above south Boulder.  Each disk looked like a yo-yo on its side, with the top section a little smaller than the bottom.  They were close enough or large enough for us to see that each one had several windows or portholes.  They moved very slowly and were visible about 10-15 seconds before they faded out of view.
I am presently a psychoanalyst in private practice.  Before I changed careers, I was chief of a large fire protection district in the western U.S.  
Before that I was a naturalist with the National Park Service, and have long been a student and observer of nature.  I consider myself to be a curious, careful and scientifically oriented observer.  
My husband was a civil engineer.