What causes turbulence and how often is it as severe as the Singapore Airlines flight?

While weather forecasts help pilots react, experts say the turbulence experienced on the Singapore flight was unexpected and rare.

What causes turbulence and how often is it as severe as the Singapore Airlines flight?

What causes turbulence and how often is it as severe as the Singapore Airlines flight?

What causes turbulence and how often is it as severe as the Singapore Airlines flight?

What causes turbulence and how often is it as severe as the Singapore Airlines flight?

What causes turbulence and how often is it as severe as the Singapore Airlines flight?