https://www.sciencedaily.com/releases/2018/05/180524141647.htm

A study published May 24 in Science offers an explanation for a mysterious and sometimes deadly weather pattern in which the jet stream, the global air currents that circle the Earth, stalls out over a region. Much like highways, the jet stream has a capacity, researchers said, and when it's exceeded, blockages form that are remarkably similar to traffic jams -- and climate forecasters can use the same math to model them both.

The deadly 2003 European heat wave, California's 2014 drought and the swing of Superstorm Sandy in 2012 that surprised forecasters -- all of these were caused by a weather phenomenon known as "blocking," in which the jet stream meanders, stopping weather systems from moving eastward. Scientists have known about it for decades, almost as long as they've known about the jet stream -- first discovered by pioneering University of Chicago meteorologist Carl-Gustaf Rossby, in fact -- but no one had a good explanation for why it happens.