The climate is temperate, but varies considerably with altitude (on average around 6.5°C every 1000m). There are four clearly defined seasons, which bring changes in both temperature and precipitation. Switzerland experiences cold, cloudy, rainy/snowy winters and moderate to hot summers, with weather that can change very quickly; especially on hot summer days and in the mountains; in extreme cases, within minutes. Some years you may experience cloudy, rainy and wet summer days, other days or even the following year very sunny, or sometimes even hot summer days with only occasional showers. About one in three days of the year is a rainy day, with either a brief shower or constant drizzle throughout the day. Forecasts made more than five days in advance are not reliable.