Friends of mine were travelling in the UK by bus once, when suddenly the bus stopped and all passengers had to get out. The driver told them that there were "snow windows" and so they couldn't proceed to Glasgow. When they said "but there's no SNOW" - all they got back was "but there are snow windows". However, no one could translate or paraphrase to them what "snow windows" are. Back home they tried to look it up in several different dictionaries, but no success. I wasn't able to find anything about it using Google either.
So what kind of weather condition are "snow windows"?