Let's say you saved and TURNED OFF the game at Snowpoint City, out in the snow. After a few hours, you turn on the game and find that some of your pokemon have been frozen.
Do you think this is likely to happen?
Of course, the reverse effect could happen. You have pokemons that are frozen. You find a house somehwere and save and turn off the game. After a few hours, you come back and find that the warmth of the house rid the frozen effect.