1999-12-10 - Sherman Oaks, CA - Other

A single small cloud moved from WNW to WSW over a 5 min. period in an otherwise clear sky. Faintly comet-shaped. Military rocket launch?

I am a computer-graphics animator with interest in weather, astronomy, space travel, etc. I watch the sky a lot, and what I saw wouldn't have raised the average person's eyebrow but I found it hard to explain. I was driving westbound on the 101 freeway at about 4:45pm on Friday, December 10. There was a very strong wind (around 30 mph) blowing out of the north. The sun had set earlier but the western sky was still bright with upward-slanting sunlight. The sky was completely cloudless (except for 2-3 cumulus clouds very far to the north end of the San Fernando Valley which were no longer lit by direct sunlight). There were a number of contrails from overflying jets (there are many major airways over the SF Valley). These all appeared as salmon and orange-colored lines of about two inches at arm's length. They didn't persist but followed close behind the jets. As I drove West through Sherman Oaks, I saw a small cloud to the WNW, a little to the right of the freeway and just above treetop level. It appeared a bit smaller than my thumbnail at arm's length. The cloud appeared to be illuminated by sunlight, but it was very fuzzy and not as dense or as detailed as a cumulus cloud. Still, it had visible volume and the side facing the sun (now hidden by the horizon) was brighter than the other side. It was not a bright orange or yellow as the nearby contrails but rather had a slight pinkish quality. It rather looked like a vaporous ball that had been smudged horizontally. I judged it to be fairly high and far away, based on the fact that it was still receiving sunlight even though all the mountains in the valley were in total shadow. It struck me as odd, being the only visible cloud in the sky, and not dispersing from winds. As I watched over a period of 5 minutes it drifted to the left of the freeway, still around treetop level and still being hit by sunlight. When I looked at the cloud with my peripheral vision it appeared to take on a cometary appearance, being pointed on the leading edge and fanning out on the trailing side. This detail wasn't as obvious with my direct vision. As time passed the cloud did seem to shrink slightly, perhaps to 3/4ths its original size. Eventually it disappeared from view, but given its path it wasn't going to pass behind any visual obstructions. I got the impression it simply stopped existing. My guess is: this was an exhaust plume from a military space launch from some facility to the north or northwest of the LA region. We've had a number beautiful upper-atmosphere tests here in recent years and I rather expected this to be another of those launches, but I didn't observe anything more than the one cloud. The quality of the cloud's density and shape was similar to the clips I've seen of rocket exhausts in the upper atmosphere/low orbit realm where there isn't any turbulence to speak of. If it was a rocket, then it must have been travelling westward from the launch point. That's unusual (but not unheard of) because most rockets lauch to the east to take advantage of the earth's rotational speed. If it wasn't a rocket, then I'm at a loss to explain it. Are there any records of a launch on that day?