Temperatures in Wilmington are somewhat moderate, with warm, humid summers and generally mild winters. During the summer the relative humidity is about 75%, and fog is not uncommon throughout the year. Average annual snowfall is close to 20 inches, but any accumulation tends to melt within a few days. Most winter precipitation comes in the form of rain or sleet. Rainfall is heaviest in the summer, stemming mostly from thunderstorms. Hurricanes moving up the coast occasionally cause heavy rain, but winds rarely reach hurricane force.