Silver disk flies level across sky, at low altitude, before dusk.

It was mid summer in the Early 90's and my father, brother and I were playing catch in our backyard in northwest Omaha.  I was around 9 or 10 at the time.  We all spotted a silver disk flying very slowly to the north or northeast at a low altitude.  It was still daylight out but it was nearing night time, and it was a perfectly clear summer day.
We lived close to Interstate 680 and Fort street, and the disk appeared to be floating, maybe 2 to 3 miles beyond the interstate.  I did not see any lights on the craft, but my father thought he saw some.  I simply remember the shape of the craft.  It appeared to have a distinct upper section and a smaller lower section.  Depending on the distance, the craft did not look very large I would have to say it was no larger than 60 feet across and 15 to 20 feet top to bottom.  The disk traveled perfectly level for a long time and made no sound whatsoever.  It then began to speed up and it then passed beyond our vision after about 6 minutes.
I remember not knowing what the craft was but thinking it was unique and cool.  I had spent much time at epply airfield because my dad worked there for a long time and I had not only flown on commercial airplanes but I had been near them and seen them close up on the ground many times.  I have never in my 30 plus years seen anything fly where this disk flew.
Witness indicates that the date of the sighting is approximate.  PD