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Regional Weather Extremes Explained

Variations in high-altitude wind patterns in the Northern Hemisphere are exposing regions of Europe, Asia and the US to different extreme weather conditions, such as month-long heat waves, cold spells, droughts and prolonged wet periods.

The high altitude winds normally blow from west to east around the planet, but do not follow a straight path. Instead the flow meanders to the north and south in a wave-like path that sucks either warm air from the tropics or cold air from the Arctic to Europe, Asia or the US. They can also influence rainfall by steering rain-laden storms.

Research published in Nature Climate Change used detailed land-based climate observations to identify episodes of abnormal temperature and rainfall from 1979–2012, and then examined the wave patterns during these events. It found that the development of these wave patterns leaves certain Northern Hemisphere regions more susceptible to different types of prolonged, extreme weather.

Co-author Prof Ian Simmonds of the University of Melbourne said that month-long heat waves, cold spells, droughts and prolonged wet periods over large areas “are strongly related to well-developed wave patterns, and that these patterns increase the chance of heat waves in western North America and central Asia, cold outbreaks in eastern North America, droughts in central North America, Europe and central Asia, and wet spells 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,” Simmonds said.