All colored regions in the hovmoller plot below depict regions where the flow is blocked according to the blocking index. The color scheme denotes the strength of the blocked flow as determined from the 500 hPa geopotential height gradient measured from the blocking ridge equatorward (denoted GHGS in blocking index definition). The presence of an intense cutoff low equatorward of the blocking ridge can act to enhance the blocking strength.

• Northern Hemisphere Blocking Forecasts and Ensemble Forecasts
  
  
• Observed Southern Hemisphere Blocking
  
  
• Southern Hemisphere Blocking Forecasts and Ensemble Forecasts
  
  
• Definition of Blocking Index
  
  
• Background and Motivation
  
  
• Blocking Climatology Northern Hemisphere and Southern Hemisphere
  
  
• Distribution of DJF Northern Hemisphere Blocking as a function of ENSO cycle