Along with the cold temperatures, you have to think about the bulkiness of the clothing you could be wearing, which will give you less range of motion. Therefore making it harder to draw back. Also, practice drawing, holding it there for a minute or so, then release the arrow. You never know when you may draw on a buck, not have a good shot, then he looks at you forcing you to freeze before you can let your draw down. This will help not only your pulling arm get stronger, but will make your front shoulder stronger too by having to hold the bow straight out.