North American winters are still delivering devastating snowstorms, with hurricane-force winds that leave thousands without power.
So it can be surprising to realize that winters are the fastest warming season across most of the U.S.
What’s going on with our winter weather?
The pace of winter warming has picked up in recent decades. From 1970 to 2017, winter in the lower 48 states warmed more than 4½ times faster per decade than it did over the past 100 years.
How warming scrambles weather patterns
Overall, a warming atmosphere means more evaporation from both land and sea, so there’s more moisture in the air — 4% more moisture per degree (F) rise in temperature.
That leads to extremes: Hotter, drier areas tend to get even drier and have less rainfall, since the evaporated moisture rarely meets the colder temps that turn water vapor into liquid. (Other factors, such as air circulation patterns, also play a role in precipitation shifts.)
In areas that do get precipitation, they get more of it: more rain (and flooding) when temps are above freezing, and when temperatures (less frequently) drop below freezing, there’s a greater chance of snowstorms that break records.
So while the average amount of snow is declining in many areas of the U.S., the amount of snow that falls during a snowstorm is increasing — more than 40% of counties in the country have had their biggest two-day snow totals on record since 1980.
Why a warming Arctic matters
Another factor could also be fueling stronger snowstorms in the eastern and southern U.S.: the jet stream.
While usually referred to as singular, there are actually two jet streams — relatively narrow bands of strong wind that blow from west to east around the globe above the Northern and Southern Hemispheres.
These jet streams run along the boundaries where hot and cold air meet. The greater the temperature differential, the greater the force of the jet stream.
In recent years, researchers have found evidence that strong warming in the Arctic — it’s heating twice as fast as the rest of the world — can weaken the northern jet stream by decreasing the temperature differential along this warm air-cold air boundary.
That makes it easier for the jet stream to be pushed and pulled out of its normal path, which can allow frigid polar air to penetrate farther south than normal.