The polar vortex, a weather feature that contributed to the Great Texas Freeze, is currently forming in the stratosphere over the North Pole and is expected to continue to strengthen rapidly as we approach the winter, according to experts at weatherandradar.com.
The last time Texas experienced a “polar vortex effect” was last winter, when a cold front brought frigid temperatures and wind chills down to -15 degrees.
The polar vortex is extensive coverage of low pressure and cold air surrounding Earth’s poles. When the vortex is strong and stable, the polar jet stream shifts northward, keeping the cold air in the Arctic. But when the vortex weakens or is disrupted, the jet stream often becomes extremely wavy, allowing warm air to flood into the Arctic and polar air to sink down into the mid-latitudes.
The polar vortex played a role in the extreme winter weather outbreak that struck Texas in February 2021, UN weather experts said.
“We did have a sudden stratospheric warming in January,” explained NOAA stratosphere expert Amy Butler. “The polar vortex weakened. It got stretched out of shape and slid southward off the pole. Most of the time when this happens — and it happens on average about every other year in the Arctic — some part of the mid-latitudes will ultimately experience a cold air outbreak. The disruption of the vortex encouraged the polar jet stream to become wavier for several weeks, and in combination with other weather patterns, created favorable conditions for a severe cold air outbreak in the central U.S.”
What exactly is the polar vortex?
While the polar vortex has always been present, the term has only recently been popularized. The polar vortex refers to the large area of low pressure and cold air surrounding both of the Earth’s poles, according to the National Weather Service. It always exists near the poles, but weakens in summer and strengthens in winter. The term refers to the counter-clockwise airflow that helps keep the colder air near the poles.
Oftentimes during wintertime in the northern hemisphere, the polar vortex expands, sending cold air southward with the jet stream. It’s often associated with large outbreaks of Arctic air in the U.S.
“There is a lot of myth and legend around the polar vortex. Actually, the polar vortex has been around forever,” meteorologist Victor Murphy at the National Weather Service in Fort Worth told the Star-Telegram. “Ordinarily, there is a belt or a band of strong west to east winds that moves around the globe at relatively high latitude, close to the pole. Once or twice a year, the belt of strong winds will buckle, or have a weakness, and the jet stream (polar Vortex) will plunge southward. With this comes frigid temperatures to the lower latitudes of the globe.”
However, plenty of Arctic cold air outbreaks happen in a given winter without any help from the polar vortex. And sometimes the polar vortex is disrupted and there are few, if any, impacts on the weather down at the surface. While the polar vortex doesn’t always influence winter weather in the U.S., the effects can be extreme when it does. Notable cold outbreaks in 2014, 1989, 1985, 1982 and 1977 have been associated with the polar vortex.
“By itself, the only danger to humans is the magnitude of how cold temperatures will get when the polar vortex expands, sending Arctic air southward into areas that are not typically that cold,” NWS writes on its website.
How has the polar vortex affected Texas?
Global warming has increased the number of polar vortex outbreaks, a study found. While they used to only happen once every other year or so, the research shows they are now close to happening yearly, if not more, said study lead author Judah Cohen, a winter storm expert for Atmospheric Environmental Research. The number of times the polar vortex has weakened per year has more than doubled since the early 1980s.
The Texas freeze of February 2021 is a “poster child” for the link between a changing Arctic and cold blasts in lower latitudes, climate scientists say.
“It is counterintuitive that a rapidly warming Arctic can lead to an increase in extreme cold in a place as far south as Texas, but the lesson from our analysis is to expect the unexpected with climate change,” Cohen told the Associated Press.