WASHINGTON -- Meteorologists may have found a way to predict some killer heat waves up to three weeks in advance. Now, the best they can do is about 10 days.
An earlier warning would help cities prepare for the heat wave, arrange to open up cooling centers and check on the elderly, said Gerald Meehl, co-author of a study that describes the forecasting clue.
The key may be a certain pattern of high and low pressure spots across the globe high in the sky. When that pattern shows up, the chances double for a prolonged and intense heat wave in the eastern two-thirds of the United States, according to the study published Sunday in the journal Nature Geoscience.
This could predict some types of heat waves but not all, meteorologists said. The study's authors said they think the pattern occurred before last year's heat wave in much of the central United States, but they still need more work to confirm it.
The researchers at the National Center for Atmospheric Research in Boulder, Colo., looked at heat waves that lasted at least a week and were about 5 to 8 degrees warmer than normal. In any given summer week, the odds of a heat wave like this happening are usually only about 1 in 67 in the U.S.
They did thousands of computer simulations and discovered that when high pressure and low pressure systems line up in a specific pattern, it foreshadows heat to come in about 15 to 20 days. Scientists call this 4-mile-high pattern wave No. 5.