If you think the weather’s a bit weird right now, you’re not wrong. The northern and eastern portions of North America are caught in a deep freeze, and the eastern seaboard is preparing for something called a “bomb cyclone.” Meanwhile, Californians are reeling from an unusually long wildfire season, and Alaskans are skating in t-shirts. So what gives?
Those of us living in North America don’t need to be reminded that the weather’s off the charts at the moment, but this temperature anomaly map from NASA’s Earth Observatory really puts the current meteorological situation into perspective.
Data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite shows land surface temperatures from December 26, 2017 to January 2, 2018, compared to the same eight-day period from 2001–2010. The redder the area, the warmer the land surface temperatures, and the bluer the area, the colder. White areas are experiencing normal temperatures, and those grey splotches show where there’s insufficient data.
Importantly, this map conveys land surface temperature anomalies, and not air temperature; these two measures are slightly different.
Other parts of the world are also experiencing temperature anomalies. Europe, parts of Asia, and the Middle East are unusually warm right now, while portions of South America and Africa are cooler than usual.
As to why we’re experiencing such extremes at the moment, NASA offers this explanation:
The map of North America underscores one of the realities of weather—when a cold snap hits one region, warmth often bakes another one. A giant meander (or Rossby wave) in the jet stream is the common thread that connects the warm weather west of the Rockies with the chill east of them. As the crest of a Rossby wave—a ridge—pushed unusually far toward Alaska in December, it dragged warm tropical air with it. In response, the other side of the wave—a trough—slid deep into the eastern United States, bringing pulses of dense, cold Arctic air south with it. The Rocky Mountains have boxed in much of the coldest, densest air, serving as a barrier between the cold and warm air masses.