National Center for Atmospheric Research scientists observed a particular sequence of five alternating low and high-pressure systems in the atmosphere far above the North Atlantic. When that pattern moved over the continental United States, it increased the chances of a heat wave.
Fall from Space: Foliage Photos
The five high-pressure systems ringed the mid-latitudes of the north like pearls on a necklace moving slowly westward. When that pattern emerged, the United States faced double to quadruple the chance of a serious heat wave after approximately 20 days. The pattern blocked movement in the atmosphere and allowed hot, dry conditions to take hold. For example, the pattern preceded the heat waves and droughts of 1952-54 and 1988.
To discern the pattern, the atmospheric scientists used weather records and atmospheric measurements since 1948. A computer simulation of 12,000 years of U.S. weather supplemented the historical observations.
NEWS: Too Late To Stop Extreme Heat Waves
The results of the weather analysis and simulation will be published in Nature Geoscience.
Top Image: Sequence of the sun setting, silhouetting a lone windmill on plains in Colorado. (Ed Darack/Corbis)