This indicator describes trends in unusually hot and cold temperatures across the United States.

This indicator examines trends in unusual temperatures from several perspectives:

• The size and frequency of prolonged heat wave events (Figure 1).
• Unusually hot summer temperatures and cold winter temperatures nationwide (Figures 2 and 3).
• The change in the number of days with unusually hot and cold temperatures at individual weather stations (Figures 4 and 5).
• Changes in record high and low temperatures (Figure 6).

The data come from thousands of weather stations across the United States. National patterns can be determined by dividing the country into a grid and examining the data for one station in each cell of the grid. This method ensures that the results are not biased toward regions that happen to have many stations close together.