While at least half the drivers for this winter’s weather can be summed up as pure chaos, well-known patterns have played their roles as well.
Start with El Niño, a periodic shift in location of a vast deep pool of warm water that migrates from the western Pacific and piles up against the west coast of South America. As the warm water travels, so do the bands of convective thunderstorms that the warm water spawns. As these storms and their strong updrafts migrate, the change alters atmospheric circulation patterns globally.
The warm waters made their move during the fall, says Tony Barnston, the lead forecaster at the Lamont-Doherty Earth Observatory’s International Research Institute for Climate and Society in Palisades, N.Y. But only recently did stronger-than-normal thunderstorm activity move east of the international date line to begin rearranging atmospheric circulation patterns.
One result: The subtropical jet stream, a high-altitude river of air that snakes its way west to east across North America, is driven farther south than normal. The jet stream acts as a superhighway for storm systems that roar in off the Pacific.