Do extreme climate events require extreme forcings?

Abstract The question whether extreme climate events require extreme forcings is assessed for the severe Great Plains drought during May–July 2012. This drought event had a rapid onset, and little indications or early warnings for its sudden emergence existed. The analysis of its origins is based on a dynamical seasonal climate forecast system where states of the ocean, atmosphere, land, sea ice, and atmospheric trace gases were initialized in late April 2012, and an ensemble of forecasts was made. Based on the diagnosis of a spectrum of possible outcomes for precipitation over the Great Plains from this system, it is concluded that the extreme Great Plains drought did not require extreme external forcings and could plausibly have arisen from atmospheric noise alone. Implications for developing early warning system for extreme events in general are also discussed.