Looking over the maps and meteorological data Teddy posted today, I think I get that the weather was in the dark blue section on Feb 1-2, which would be very strong winds. Maybe a storm? The tent did remain in place, though, so with strong winds outside, the hikers would have understood that it would be best to stay put and not venture out. (That is, if I read the geological maps correctly and that has never been my strong point.)
Just a thought: If there was a storm known as "thundersnow," and with the magnetic anomaly of the Urals, lightning and plasma balls (seen by the hikers at Mt. Chitsop) could have developed.