The theory is not that UPS902 descended enough to cease creating a contrail, but that it passed from cold moist air over the Pacific to drier warmer air (changing the dew point) as it approached land.
That's the theory now. Last week it was that UPS902 dropped from 39,000 ft to 37,000 ft. Oddly enough their source for that, FlightAware.com now shows that flight, on Nov. 8th, traveling most of its flight at 37k ft and ascending to 39k ft for the last portion of its flight.
Even the contrailscience guy used that argument on his Youtube page.
# EpoxynousEpoxynous
2 weeks ago@zerotolerance4u That's the average cruising altitude. You need to click on "Tack log and graph" UPS902 was at 39000 feet from 4PM PST (listed as 7PM EST)
FWIW, DoorGunner, I tried to find weather info for that date everywhere I could and none was available that I could find. I do know that a huge front had come in from the Pacific at that time and was over the Front Range of the Rockies in Colorado at 5:00 PM PST. I know because the humidity in it was coming down in white flakes here.