U.S. Climate Extremes Index

The U.S. Climate Extremes Index documents the area of the contiguous United States that experienced extreme conditions during various time periods. The index is calculated as the arithmetic average of values from a specified set of extreme events, weighted by the percent area that experienced the defined conditions.

• A value of 0% for the Climate Extremes Index indicates that no portion of the country experienced extremes during the selected period of record.
• In contrast, a value of 100% would mean that the entire country experienced extreme conditions throughout the period of record for all of the indicators, a virtually impossible scenario. 

The long-term variation or change of this index represents the tendency for extremes of climate to either decrease, increase, or remain the same.