The United States saw a record low tornado count in November, and scientists aren’t quite sure why.
Only 837 confirmed tornadoes have been reported so far this year, compared to an average 1,000, indicating a record low tornado count for 2016. Only one tornado has been reported in November, compared to an average of 58 in November in the 20 years between 1991 and 2010, according to the National Oceanic and Atmospheric Administration.
Scientists don’t have an answer for why the number of tornadoes has dropped – but they have several different theories.
One is that the drop is due to climate change and melting sea ice in the Arctic Circle. While natural weather variations can’t be discounted, melting sea ice and changing climate appears to have kept the usual fall storm track in Canada this year, Dr. Victor Gensini of the College of DuPage Next Generation Weather Lab told the Washington Post.
Studies have shown a potential link between melting sea ice, unusual behavior in the jet stream, and an unstable polar vortex, according to scientists.
El Niño could also be the culprit. New research has linked the El Niño/La Niña cycle to variations in the number of tornadoes and hailstorms, said Dr. John Allen of the International Research Institute for Climate and Society at Columbia University.
Moderate to severe drought conditions in the Southwest and parts of the Midwest and southeastern United States could also play a role, scientists said. Without storms, tornadoes can’t form, and storms don’t happen without humidity.
A high pressure ridge blocking the jet stream is probably the largest player, however, said Allen. The ridge has been sitting over the Great Plains and southeast since September, he noted, blocking the jet stream from entering the U.S. from Canada.
Whatever the causes, areas that face regular tornado dangers are probably grateful. But scientists will continue to watch the unusual lack of activity to determine whether it’s simply a weather variation or a sign of a wider pattern of climate change.