 The crew had foggy mornings just on the days they needed them, and  the fog lingered only so long as it was needed to complete the  scenes. Snow was written in the script for one sequence, never  really thinking that it would actually happen. It normally snows  hard enough to actually be visible on film 4 or 5 times a year. When  they needed it, the snow came down in huge flakes just until the  director said "Cut" on the last take, and then it stopped.