No doubt it's been unseasonably cold over the past six weeks...and we're not alone. Much of the central U.S. has been colder than normal, even fueling a November blizzard that obliterated records that have lasted a century or more.
But that's the weather, not the climate.
We must always consider that the weather is the lower atmospheric conditions at the hour, week, day, or week time frame. Climate is the average weather over months, years, decades, and centuries.
When looking for reasons for our harshly cold weather, the answer is the warming climate.
Warming water in the Pacific Ocean has caused the main branch of the jet stream to become more amplified. Instead of a west-to-east pattern, we are seeing very large pushes from south-to-north and in response, north-to-south.
This amplified jet stream is the reason why California is seeing more wildfires, more often. While some of the fires have been caused by arson and some are worse thanks to poor land management, climate change is having a more significant effect. And instead of having a "fire season," the west's fires are happening all year long.
Farther north on the coast, the amplified pattern is accelerating the melting of the Alaskan glaciers.
The influx of warm air into Alaska is causing a dislodging effect of the cold air. This triggers more frequent spells of colder air into Central Canada and the U.S. east of the Rocky Mountains. It's too early to tell whether this pattern will dominate the winter season. Long range forecasts still point to a warmer and drier forecast for the Central U.S.
An analysis of temperatures in Illinois and Iowa by Climate Central shows winter definitely warmer, on average, than they used to be. Since 1970, winters have warmed about 4 degrees Fahrenheit. That's an incredible rise! However, summers aren't warming at nearly the alarming rate that winters are. In Iowa, summers are not even warmer than they were back in 1970. That is largely attributed to the fact that the state's land use is overwhelmingly agricultural. Moisture from plants (largely soy and corn) keeps moisture in check, which doesn't allow for long-term warm extremes.
Looking at the continental U.S., 37 states are seeing winters warmer than normal with all of those states east of the Rocky Mountains.
-Meteorologist Eric Sorensen