When filming The Empire Strikes Back in Norway, an intense snowstorm hit the hotel the cast and crew were staying in. Director Irvin Kershner thought it would be the perfect chance to film Luke wandering into the snow from the Wampa cave. He sent Hamill out into the snowstorm while he and the production crew filmed, nice and cozy, from inside the hotel.
#19 there was a lot more to it than that