The extreme cold, snow and icy conditions that are blasting much of the U.S. this week are a complicated blend of atmospheric, climatological and oceanographic conditions. It is a one-two punch of human-caused climate impacts and natural weather patterns.
Here’s a study session breakdown from your in-house scientist:
Normally, there’s a big temperature difference between the Great Lakes region and the Arctic (thank goodness), with the polar jet stream bringing winter air from the southern Alaskan and Canadian latitudes.
“ We call this a polar front. Front means there's a very strong temperature gradient blocking the Arctic cold air from penetrating into our mid latitude like [the] Great Lakes [region],” said Jia Wang, an ice climatologist who studies both the Great Lakes and the Arctic regions.
When bodies of air are dramatically different temperatures, they’re less likely to mix. In the same way that the cold milk temporarily stays separate from the hot coffee when you pour them together. But as they combine and their temperatures become less different, they begin to mix.
Climate change is warming the Arctic nearly four times faster than the rest of the planet. This warming of the Arctic means there’s less of a temperature difference between the bodies of air, and less difference means more mixing, weakening the jet stream. As a result, it dips down, allowing the polar vortex to stretch over the U.S. This week, it is bringing air from farther north in the Arctic (which, despite warming, is still far colder) to Michigan.
But climate change is just a slice of this frozen pie. We also have natural variability that is compounding the conditions.
The first one is called the North Atlantic Oscillation (NAO) index.
This is based on something called surface sea-level pressure.
This is a good time to remind you that the earth is a sphere spinning in space, with land surrounded by oceans, and sea level is not a flat constant globally. Sea level pressure is the atmospheric pressure at sea level in whatever location you’re measuring. High or low pressure systems can impact our daily weather by pushing fronts. The NAO is based on the pressure difference between two systems over the Atlantic Ocean.
According to NOAA’s observed NAO index, we are currently experiencing a negative NAO phase. In North America, this is associated with below normal temperatures in the eastern U.S. and increased storms.
Secondly, the Northern Hemisphere is currently experiencing La Niña conditions. La Niña is part of a natural climatic cycle called the El Niño Southern Oscillation (ENSO). ENSO cycles are called La Niña and El Niño, and they bring extreme weather. La Niña is associated with extreme cold events in the northern U.S.
In the Great Lakes region, we have one more added layer of fun called lake effect. Last year, Wang and his colleagues published a paper analyzing lake surface temperature extremes. They modeled lake physics and thermodynamics and examined the relationship between lake temperatures, heat waves and cold spells. While there is a general warming trend, they also found an increase in extreme temperature events. For example, variability in lake ice cover was linked to these extreme events, which can have follow-on effects like increased heat waves in the summer.
As a bonus, if the weather significantly cools the lakes, the region could expect more lake effect snow.
