Which type of turbulence is indicated as severe or extreme in urgent PIREPs?

Severe or extreme turbulence is typically associated with clear air turbulence, which can occur unexpectedly and without visual cues such as clouds, making it particularly dangerous. Clear air turbulence generally happens at high altitudes, often at the jet stream level, and is influenced by various atmospheric factors like wind shear, mountainous terrain, and weather fronts.

In urgent Pilot Reports (PIREPs), pilots may report this type of turbulence due to its potential to cause significant altitude changes and is challenging for pilots to predict or avoid. The other types of turbulence, such as light and moderate turbulence, are generally less severe and do not pose the same level of risk, which is why they would not be classified as severe or extreme in the context of PIREPs.