A thunderstorm is a complex meteorological event, characterised by the presence of electrical discharges (lightning) followed by thunder. The conditions needed for a thunderstorm to develop are a sufficient level of humidity and the rapid upward movement of air, e.g. as a result of being warmed. Inside a storm cloud (cumulonimbus) there are often strong updrafts and downdrafts, which cause turbulence. Hazardous weather events that can occur in a thunderstorm include lightning, heavy precipitation (downpour of rain, hail, graupel/snow pellets, and, in winter, snow) as well as wind gusts that can sometimes reach up to hurricane strength.
Danger levels thunderstorms
|Danger level 5 (very severe danger)|
|Thunderstorm warnings are only issued for categories 3 and 4. In spite of the most up-to-date tools and methods, it is not currently possible to predict or give several hours’ warning of the strength, timing and location of severe thunderstorms. Three of the categories are therefore of little significance.|
|Danger level 4 (severe danger)|
|Behaviour||Information on recommended actions can be found here: What to do during a thunderstorm|
|Description of measurement and prognostic values||
|Danger level 3 (significant danger)|
Information on recommended actions can be found here: What to do during a thunderstorm
of measurement and prognostic values
|Danger level 2 (moderate danger)|
|A thunderstorm event that is usual for the time of year (for which, therefore, no special warnings are issued)|
“Flash thunderstorm” is the term used to describe short-term warnings (0 to 2 hours) within a more localised region. This warning is only issued once the intensity of a thunderstorm cell has reached the corresponding category. At least one of the criteria of hail, wind or rain (see table) must be met in order for a particular thunderstorm warning to be issued.
- Description of the danger levels of MeteoSwiss (german version)