Thunderstorm — lightning, thunder and cumulonimbus
Thunderstorms are among the most powerful weather systems we experience in Norway. Enormous amounts of energy are released in a short time — with spectacular and sometimes dangerous consequences.
📅 23. May 2026
Cumulonimbus — the thundercloud
All thunderstorms are associated with the cumulonimbus cloud — the most powerful of all cloud types. This cloud can extend from a few hundred metres altitude up to 15 to 18 kilometres, where the top flattens into the characteristic anvil shape against the tropopause. Inside the cloud, extremely powerful vertical air currents exist — updraft columns can reach 150 to 300 km/h.
How does lightning form?
Inside the cumulonimbus cloud, electrical separation occurs. Heavy ice particles and hailstones fall downward and become negatively charged, while light ice crystals are carried upward by the wind and become positively charged. When the voltage difference becomes large enough — typically hundreds of millions of volts — it equalises in an electrical discharge we call lightning. The temperature in the lightning channel can reach over 30,000°C — five times hotter than the surface of the sun.
Thunder
Thunder is the sound of air expanding explosively around the glowing lightning channel. Since sound travels much more slowly than light (340 m/s versus 300,000 km/s), we hear the thunder after the lightning. The rule of thumb: count the seconds between lightning and thunder and divide by 3 — this gives the distance in kilometres.
Types of lightning
There are several types of lightning. Cloud-to-ground lightning is the most well-known and dangerous. Cloud-to-cloud lightning is actually more common and illuminates the entire cloud layer. Ball lightning is a rare and poorly understood phenomenon in which a luminous area moves through the air for seconds to minutes.
Thunderstorms in Nordmøre
Nordmøre experiences thunderstorms primarily in summer, but also in autumn when sea temperatures are high and cold Arctic air flows in. Convective thunderstorms (on warm days) are most common in July–August. Winter thunderstorms (thundersnow) are rare but do occur along the coast.
Safety
During a thunderstorm: seek shelter indoors or in a car. Avoid open terrain, tall trees and water. If you are outside and cannot find shelter, crouch down with your feet together — do not lie flat. Wait 30 minutes after the last thunder before going outside again.