Weather is a set of all the phenomena occurring in a given atmosphere at a given time. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate is the term for the average atmospheric conditions over longer periods of time.When used without qualification, "weather" is understood to be the weather of Earth.
Weather occurs due to density (temperature and moisture) differences between one place and another. These differences can occur due to the sun angle at any particular spot, which varies by latitude from the tropics. The strong temperature contrast between polar and tropical air gives rise to the jet stream. Weather systems in the mid-latitudes, such as extratropical cyclones, are caused by instabilities of the jet stream flow. Because the Earth's axis is tilted relative to its orbital plane, sunlight is incident at different angles at different times of the year. On Earth's surface, temperatures usually range ±40 °C annually.
Source: en.wikipedia.org/wiki/Weather - 25.03.2010
Whether concentrated discharge of energy, refreshing wind, gentle spring-air, full rain, extreme midday heat or snowstorm: all these or more we call weather.
A small word for such a variety of natural phenomena.