Gandalf halted. Snow was thick on his hood and shoulders; it was already ankle-deep about his boots."This is what I feared,' he said. `What do you say now, Aragorn?'
'That I feared it too,' Aragorn answered, `but less than other things. I knew the risk of snow, though it seldom falls heavily so far south, save high up in the mountains. But we are not high yet; we are still far down, where the paths are usually open all the winter.'
'I wonder if this is a contrivance of the Enemy,' said Boromir. "They say in my land that he can govern the storms in the Mountains of Shadow that stand upon the borders of Mordor. He has strange powers and many allies.'
'His arm has grown long indeed,' said Gimli, `if he can draw snow down from the North to trouble us here three hundred leagues away.'
'His arm has grown long,' said Gandalf.
I don't have my books so I can't reference it for sure.
I guess it could be like a standing order not to let anyone across or it could be directed at this group, but do either of the evil minds know for sure what is up with the fellowship at this time?