Over time, pavement cracks and breaks due to moisture build up or wear and tear from traffic. Water trapped between the cracks causes erosion and the pavement to sink down and break, resulting in a pothole.
In winter, water under pavements freezes and expands, then thaws and contracts. This cycle accelerates pavement deterioration and increases the incidence of potholes, making them more prevalent during winter months.
When it is cold or wet outside, the material used to patch potholes does not adhere well to the surrounding pavement. Pothole repairs made under these conditions may not last very long but are necessary for safety reasons. More permanent street repairs takes place in the warmer months when hot asphalt becomes available.