The Metoffice has just produced an excellent article on the causes of the Bodmin snow blizzard of November 2005.  I remember it well as I ended up trapped in Bodmin trying to get home to Launceston and ended up staying in Bodmin with other teachers.  It took 4 hours to travel from one side of Bodmin to the other.  We went in to a sunny clear day and by lunchtime the snow was drifting around the school and the students and staff were having great fun with snow ball fights!