Potholes most often form during the spring.  If temperatures vary which are common during the winter, potholes will be more likely to form.  Additionally, the use of chemicals (depending where you live) on the roads actually contributes to the occurrence of potholes.  Chemicals like salt lower the temperature in which water freezes.  This causes water to pass back and forth between the freezing temperatures more often, thus wearing away the road surface faster. And that is how potholes form!