My first guess was snowmaking but after watching it again today I think it may be exhaust from heating one or more of the slopeside lodges. Another guess would be- when we hiked the Sugarloafs just west of the Rosebrooks back on January 2nd there was quite a bit of logging activity along Zealand Road. I don't know how much diesel exhaust this would generate, but it may be a contributing factor. Open water on the Ammonoosuc and Zealand Rivers could also be accomplices. It may be a combination of all these factors.