It takes about two weeks to get acclimatized to a warmer environment. While we'd all love to arrive two weeks early at a warm weather racing destination, that's not always possible. So how can you adjust to warm weather when it's still freezing in your training location?
As long as you have access to a treadmill, you can work on getting acclimatized. Treadmill runs are also a good chance to experiment with race outfits, since you'll most likely be wearing different running clothes than you've worn during your chilly training runs.
To get the most out of acclimatization, your indoor runs should be as close as possible to your race because you do lose the benefits you gain if you don't maintain the heat exposure. So, it's not necessary to do all your training on the treadmill. About three weeks before your race, move indoors for at least three of your runs. If you're training for a half marathon or marathon, make sure at least one of those runs is your long run. Repeat the same routine two weeks before your race, and do one of your shorter runs at your goal race pace. The week before your race, do three short runs indoors.
Make sure you're well-hydrated during the week leading up to the race, especially on route to your race destination and once you get there. The day (or days, if you're there earlier) before your race, walk around or go for an easy run outdoors so you're exposed to the change in temperature and humidity.