I'm a serious skeptic but at the moment this is a UFO

We were driving home tonight about 10:15. We were heading south on SE 174th just north of Powell when we saw flashes in the sky. We pulled over to see if we could see what it was and, from our vantage point looking just west of south, it appeared that there was a helicopter hovering over Powell at about 170th and that it was firing off a strobe of some sort. The color of the flashes looked more like fire (yellow) than like illumination and I had the impression at first that they were circular as you would see looking at a 'flashbulb'. We watched for three or four minutes trying to hear any sound of helicopter blades. There was not any sound. The shape of the object still appeared to be helicopter sized but there not clear running lights and the flashing didn't recur right away. At this point, the object appeared to be drifting in a north-northwest direction and passed overhead and just to the west of us. Still no sound. Occasionally there was a flash of bright light again or two but not strobelike. I called my brother who lives almost due west of us at about 90th and asked him to go out and look as the object was getting farther away still appearing to be slowly drifting on an air current---straight line. My brother called back and was looking with his binoculars but couldn't find anything. The object was, at that point too far to identify in the lighthaze west of me. I looked at my clock at that point and it was 10:27 so we'd been watching for probably fifteen minutes. A small plane on a somewhat parallel course in the opposite direction had come out of the northwest heading to the southeast about five minutes earlier and its engine sounds were clearly identifiable.

The only scenario I could envision for this event was that a hot air balloon was drifting and was having fire problems with its propane system, but the shape of the object and the inconsistency of the flashes didn't fit and the fact that it was a December night also made it unlikely.

Anyone have any ideas about what it might have been? I am a very skeptical person, but this was definitely--at the moment---an unidentified flying object to me.

I would welcome any other thoughts or information.