Most people in the eastern and central U.S. have clear memories of this past winter – unseasonably cold, and seemingly endless, it’s not anything anyone remembers fondly. For whatever small amount of solace it’s worth, scientists from the University of Exeter and the University of Melbourne have found a cause: Prolonged extreme weather patterns (drought, heat waves, cold snaps) are the result of variations in high-altitude wind patterns.

“The impacts of large and slow moving atmospheric waves are different in different places. In some places amplified waves increase the chance of unusually hot conditions, and in others the risk of cold, wet or dry conditions,” said Dr James Screen, a Mathematics Research Fellow at the University of Exeter and lead author of the study.

Typically, high-altitude winds travel around the Northern Hemisphere from east to west. However, they don’t do so in a straight line – their movements are more wave-like, dipping to the south in some areas and further north in others. Depending on the wave patter, that determines whether the winds draw up more warm air from the equator, or cold air from the Arctic.

Changes in the wave patterns can have major effects here on the ground, as evidenced by last winter’s harsh conditions. The study showed that larger waves can lead to droughts in central North America, Europe and central Asia. It also shows western North America and central Asia are more prone to heat waves, while eastern North America is more likely to experience prolonged outbreaks of cold.

Sound familiar? They also found that by steering rain systems, the wave patterns leave some areas susceptible to heavy rain and flooding, as experienced in western Asia.

“The findings are very important for decision makers in assessing the risk of, and planning for the impacts of, extreme weather events in the future,” said co-author Ian Simmonds, Professor of Earth Sciences at the University of Melbourne.

Of course, the scientists left out the most important parts: Why this happens (other studies have linked the phenomenon to climate change, but not conclusively), and what, if anything, can be done about it.