20th century trends in temperature and precipitation will be shown for each U.S. region, with a focus on extreme climate conditions, such as heat and cold waves, which have trended in opposite directions, as well as heavy precipitation events, which have tended to increase during recent years in eastern parts of the United States.
Projections of 21st century climate under selected emissions scenarios will also be presented. Such simulations indicate a shift towards warmer conditions across the U.S., including both an increase in the number of hot days and nights, and a decrease in the number of cold days and nights. Projections of annual average precipitation do not provide a robust signal of either increases or decreases for most regions, however, simulations of extreme rainfall indicate future increases of 20% or more in the magnitude of the largest rainfall events under a high emissions scenario. Also, the length of dry spells is projected to increase in most areas.