Weather is the state of the atmosphere at a particular place and time. It includes temperature, humidity, precipitation, cloudiness, visibility, and wind. Unlike climate, which describes long-term averages, weather changes from hour to hour and day to day.

Weather systems develop, move, and dissipate under the influence of large-scale pressure patterns, temperature contrasts, and moisture availability. Local effects such as mountains, coasts, and urban areas further modify the conditions experienced at any single location.

People plan daily activities around the weather forecast. Accurate observations and predictions reduce the impact of hazardous conditions and support sectors from agriculture to aviation. The study of weather is the core of synoptic and mesoscale meteorology.

Every forecast begins with understanding the current weather and the processes that will change it.