A thunderstorm is a meteorological phenomenon which is accompanied by electrical discharge and thunder. Characteristic of thunderstorms are clouds with a huge vertical expansion (Cumulonimbus). Thunderstorms arise by quick ascension of warm and humid air and its fast cooling. Thunderstorms are often accompanied by heavy rain, strengthening wind and hail and have several triggers: thermal, orographic and dynamic. The thermal trigger is the sun (mainly in summer) or a warm water surface (in autumn and winter). Thunderstorms can also build due to orographic ascension along mountains. We divide two kinds of thunderstorms: frontal thunderstorms and heat thunderstorms. Frontal thunderstorms build with fronts and move with them, even over a long distance, while heat thunderstorms are locally limited. They build where the updraft is very high, e.g. thru heating-up the earth surface.