The mean annual temperatures in Wales are about on the coast and in low-lying inland areas. It becomes cooler at higher altitudes, with a mean decrease in annual temperatures of approximately for each of increased altitude. Consequently, the higher parts of Snowdonia experience mean annual temperatures of . At nights, the coldest conditions occur when there is little wind and no cloud cover, especially when the ground is snow-clad; the lowest temperature recorded in Wales was in conditions of this sort at Rhayader on New Year's Day, 1940, when the temperature fell to . Occasionally, the coastal area of North Wales experiences some of the warmest winter conditions in the United Kingdom, with temperatures up to ; these result from a Foehn wind, a south-westerly airflow warming up as it descends from the mountains of Snowdonia.