Mistake #4: Shooting for a PR.
You can’t keep the same goals you had for your dream cloudy, 73-degree day. Get more realistic about the pace you had in mind and adjust performance goals according to the temperature. Don’t base goal race pace on miles per hour. Instead, go by power (if available), heart rate or simply perceived exertion. Forcing your body to adhere to a set pace regardless of weather conditions will make you more susceptible to dehydration and exhaustion.