Weather is the state of the atmosphere at some place and time. We describe the weather in many ways. For example, we may refer to the temperature of the air, whether the sky is clear or cloudy, how hard the wind is blowing, or whether it is raining or snowing. At any given time, the weather is fair in some places, while it rains or snows in others. In some places it is warm, and in others it is cold.
Earth is not the only planet with a variety of weather conditions. All of the planets in the solar system larger than Mercury have enough of an atmosphere to support weather systems. In addition, Titan, a moon of the planet Saturn, has such an atmosphere. The remainder of this article discusses the weather on Earth.
The weather affects our lives every day. For example, it can have an impact on what type of clothing we wear and how we spend our free time. Weather also affects agriculture, transportation, and industry. Freezing temperatures can damage crops in citrus-growing regions, causing a rise in the price of oranges. Winter snows often create hazardous driving conditions. Thick fog may slow traffic on the roads and cause delays at airports. Our use of air conditioning during heat waves and heating during cold weather means that utility companies must supply more power at those times. Severe weather, such as tornadoes, hurricanes, and blizzards, can damage property and take lives.
Because of weather's importance, meteorologists (scientists who study the atmosphere and the weather) have developed ways to forecast weather conditions. Forecasts for the next 12 to 24 hours are correct more than 80 percent of the time. Long-range forecasts for the next week or month are less accurate. These forecasts indicate general trends, such as whether or not temperatures are expected to be warmer or colder than normal.
Closely related to weather is climate. Climate is the weather of a place averaged over a length of time. Scientists determine a region's climate by examining its vegetation, average monthly and annual temperature, and average monthly and annual precipitation. Earth's surface is a patchwork of climate zones. For example, in various parts of Earth, we find deserts; tropical rain forests; prairies; forests of cone-bearing trees; frozen, treeless plains; and coverings of glacial ice. Unlike changes in the weather, which can occur in minutes, climate changes generally take many years.
