From AMS Glossary
- The state of the atmosphere, mainly with respect to its effects upon life and human activities.
As distinguished from climate, weather consists of the short-term (minutes to days) variations in the atmosphere. Popularly, weather is thought of in terms of temperature, humidity, precipitation, cloudiness, visibility, and wind.
- As used in the taking of surface weather observations, a category of individual and combined atmospheric phenomena that must be drawn upon to describe the local atmospheric activity at the time of observation.
Listed weather types include tornado, waterspout, funnel cloud, thunderstorm and severe storm, liquid precipitation (drizzle, rain, rain showers), freezing precipitation (freezing drizzle, freezing rain), and frozen precipitation (snow, snow pellets, snow grains, hail, ice pellets, ice crystals). These elements, with the exception of the first three, are denoted by a letter code in the observation. With the METAR code, reporting weather also includes an intensity qualifier (light, moderate, or heavy) or proximity qualifier. The weather used in synoptic weather observations and marine weather observations is reported in two categories, "present weather" and "past weather." The "present weather" table consists of 100 possible conditions, with 10 possibilities for "past weather"; both are encoded numerically. Another method, which has the advantage of being independent of language, is the recording of weather types using symbols. There are 100 symbols that identify with the numeric codes of the synoptic observation.