On Fri, 18 Dec 2009 14:25:16 +0000, Will Hand wrote:

Before you set off in snow - clear the bonnet, roof and front and rear
windscreen of all snow as if you stop suddenly any snow on the roof will
lurch forward over the windscreen and cover your view completely.

Not to mention, solidify in the cold air-stream and slide or get blown off
into he windscreen of the car behind.