The main drawback to tracking Chemtrails using Flight Explorer is that military flights are filtered out by the FAA. Such a flight would appear in the sky, but not on Flight Explorer at all. The two instances presented here are cases where highly persistent trail segments where left by these unidentifiable flights.
This jet did not show up on Flight Explorer making it mostly likely a military jet. It was observed leaving a highly-persistent trail strip as it traveled northward.
Close-up of unidentifiable jet just after leaving trail strip. This contrail had about 20 seconds of persistence. This is slightly longer but consistent with a Boeing 757, flight AAL1596, which was leaving a 10 second contrail at 37,000 ft. at the same time. This contrail is approximately 3 miles long.
Trail strip and the end of the jet contrail on the right.
Close-up of trail segment approximately 5 minutes after it was produced. This strip is approximately 1.5 miles long.
Close-up of trail segment approximately 15 minutes after it was produced, drifting slowly to the east.
12/2/2000, at 11:00 am, two jets flying in formation leave highly persistent trail strips. These jets were confirmed to not appear on Flight Explorer.
12/2/2000, at 11:00 am, middle section of these parallel trails from unidentifiable jets.
12/2/2000, at 11:00 am, other end of two highly persistent trail strips. Trails quickly fade to nothing, just beyond right edge of photo and eventually become a wispy cirrus aviaticus cloud.