The term “weather” refers to the temporary conditions of the atmosphere, the layer of air that surrounds Earth and is referenced to a particular location and moment.
The fundamental cause of weather is the effect of the sun on Earth. At any time, only half of Earth is warmed by the sun, while Earth’s other side is shadowed. This causes uneven heating of Earth’s surface by the sun every day, with some regions warmer than others.
These temperature differences cause weather: winds, clouds and precipitation. Seasonal weather patterns result from variations in temperature caused by Earth’s tilt toward the sun in summer and away from the sun in winter. The distribution of water and land, and the topography of the land, also contribute to the shaping of Earth’s weather patterns.
Six main variables describe weather: temperature, atmospheric pressure, wind, humidity, precipitation and cloudiness. Knowledge of how these variables change, through the action of atmospheric processes governed by the laws of physics, help forecasters to predict weather.
In the modern era, meteorologists also use computer-generated forecasts as a guide, and interpret that guidance using their knowledge of weather processes.
Weather at one location is often related to weather at other locations. So, an important part of studying and understanding the weather is seeing how observations of the atmosphere relate to each other geographically. A list of numbers doesn’t help much; we need a map.
Meteorologists represent weather at a particular location and time using the station model. This model is a clever method of representing many weather variables, including cloud cover and type, wind speed and direction, temperature, dew point temperature, visibility, precipitation type and intensity, atmospheric pressure, and the change in pressure over the last three hours in one visual. A weather map is filled with symbols indicating different types of weather systems.