Atmospheric Wave Pattern May Help Predict US Heat Waves Weeks in Advance

Researchers have identified an atmospheric wave pattern above the Northern Hemisphere that, they say, could potentially help predict the onslaught of US heat waves nearly three weeks out.

The researchers from the National Center for Atmospheric Research (NCAR) discovered the pattern by studying a 12,000-year atmospheric simulation over the continent. Whenever a so-called "wavenumber-5" pattern emerged, a summertime heat wave was more likely to form. In all, the researchers looked at nearly 6,000 US heat waves simulated in a computer model to substantiate this finding.

During the 20 days leading up to a heat wave, the five ridges and troughs that comprise a wavenumber-5 pattern often moved slowly westward around the globe, the researchers found. The pattern is derived from naturally varying conditions within the atmosphere, and is related to a phenomenon known as a Rossby wave train, which encircle the Northern Hemisphere.

The report is part of an overall objective of forecasting the likelihood of extreme events more than 10 days in advance, with previous research focusing on the tropics.

"There may be sources of predictability that we are not yet aware of," NCAR scientist Haiyan Teng, the lead author, said in a statement. "This brings us hope that the likelihood of extreme weather events that are damaging to society can be predicted further in advance."

Heat waves are one of nature's most deadly events. More than 600 people died in California alone when a 2006 heat wave engulfed much of the United States and Canada, and as many as 50,000 may have died due to one that sat over Europe in 2003.

"It may be useful to monitor the atmosphere, looking for this pattern, if we find that it precedes heat waves in a predictable way," Teng said "This gives us a potential source to predict heat waves beyond the typical range of weather forecasts."