In reply to SouthernSteve:
> As the previous poster says, you need them with you and need to know when to put them on, but you might not!
Good answer.
I would add that it's not just snow the OP needs to worry about. Ice can be lethal, even on an "easy" path up and "easy" mountain. About 10 years ago I set off up the easy path on Pen y Fan from the Storey Arms car park. No snow anywhere, but the path was a lethal sheet of overlapping ice. We were sliding all over the place and people were going down like ninepins. It was impossible to make progress without crampons, and we soon put them on.
Apart from the clue of the very low temperature, there had been no indication of these conditions when we left the car.