Tuesday, March 16th 2021, 3:00 pm - This past winter, however, was one of the warmest for the continent over the past century.
This winter was marked by some extreme temperature swings across North America. After Canada experienced "staggering warmth" in January, frigid temperatures engulfed nearly the entire continent to result in the coldest February seen in decades.
According to NOAA's latest climate summary, the month of February 2021 was the coldest seen for the globe since 2014. The La Niña in the equatorial Pacific Ocean was partly responsible. The extreme cold that gripped both North America and northern Russia also played a substantial role.
Global temperature anomalies for February 2021. While record hot temperatures were recorded across the Arctic and central Asia, some regions of the world experienced extreme cold. Credit: NOAA
Looking solely at North America, the last time this region of the world experienced a colder February was 27 years ago, in 1994, based on NOAA's records.
February temperature anomalies, for the globe (top) and North America (bottom), from 1880-2021. Credit: NOAA NCEI
The cause of this continent-affecting cold snap? A meteorological phenomenon known as Sudden Stratospheric Warming, which resulted in a lobe of the infamous polar vortex taking a deep dive towards the south.
As meteorologist Tyler Hamilton wrote: "On January 5th, the typical westerly winds circling the North Pole 30 km above the surface switched direction. That triggered a sudden stratospheric warming event, a warming of the stratosphere over the pole. The main actor, the polar vortex, is the connection between the highest echelons of the stratosphere to the world of weather in the troposphere."
"One glance at a popular teleconnection, the Arctic Oscillation, gives us clues to see how wonky and wavy the jet stream has been behaving," explained Hamilton. "It's an outstanding tool to visualize just how predisposed the atmosphere is to shunt frigid air south."
"When the Arctic Oscillation is strongly negative, the atmosphere has an abundance of high pressure near the North Pole, with a lower pressure at lower latitudes; this was an atmospheric traffic jam of sorts, as the perfect ingredients came together to trap the cold in for an extended duration."
Once this negative pattern of the arctic oscillation was set up, it allowed frigid air to "flow south like molasses from Canada," as Hamilton put it. It also slowed down the entire west-to-east flow of weather across the continent.
As a result, this cold air had a full week to expand as far south as Texas and stayed locked in place there for days.
*This surface temperature map shows the extent of the cold over North America on February 19, 2021. Credit: Climate Reanalyzer/University of Maine.
__DESPITE FEBRUARY COLD, ONE OF THE WARMEST WINTERS
These cold snaps had little impact on the winter season as a whole, however. For both the northern hemisphere and globally, NOAA ranked this as the 8th warmest winter on record.
Global temperature anomalies for Winter 2021 (top) show that February's extreme cold had only a small effect on the season as a whole. Extreme warmth over North America in December and January (bottom row) balanced out the cold. Credit: NOAA NCEI/Scott Sutherland
In North America, even after enduring severe cold in February, the tally of December, January, and February temperatures still placed this winter season as the 11th warmest of the past century. It missed out on being logged in the top 10 warmest by just a narrow margin.
The extreme warmth across Canada during much of the season — especially in eastern regions of the country — played a significant role in keeping this winter among the warmest in the record books.