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What Is The Polar Vortex?

The term “polar vortex” often evokes images of bone-chilling Arctic air sweeping across the United States. But is the polar vortex responsible for this particular cold air outbreak? As temperatures fluctuate significantly this winter and severe weather events seem to occur more frequently, understanding the polar vortex’s role is key.

What is the Polar Vortex?

The polar vortex is a large section of low pressure and cold air circulating both of Earth’s poles. It always exists near the poles, strengthening during winter and weakening during summer. The “vortex” refers to the counterclockwise flow of air that helps keep colder air confined near the poles.

However, during the winter in the northern hemisphere, the polar vortex can expand and send cold air southward, leading to outbreaks of Arctic air across the United States. This phenomenon often results in significant temperature drops and winter storms.

Recent Arctic Oscillation and Polar Vortex Activity

According to the Atmospheric and Environmental Research (AER) latest report, the Arctic Oscillation (AO) is currently neutral and is predicted to remain neutral to positive over the next two weeks. This suggests mixed pressure and geopotential height anomalies across the Arctic, which influence the behavior of the polar vortex. The North Atlantic Oscillation (NAO) is trending from negative to positive, supporting a shift in temperature patterns across Europe and North America.

The AER notes that this winter has been characterized by rapid transitions in the polar vortex’s structure, alternating between a stretched PV, a circular shape, and a phenomenon known as “Canadian warming.” These transitions have occurred at breakneck speed, maintaining a near-infinite loop of changes. For example, the sixth stretched PV of the season is expected around January 15–16, followed quickly by a seventh stretching event beginning on January 20.

These rapid shifts contribute to a dynamic weather pattern, with temperatures turning colder across Canada and the U.S. this week. Next week, below-normal temperatures will become more widespread across the U.S., while Alaska sees above-normal temperatures.

How the Polar Vortex Affects Weather

Typically, a strong and stable polar vortex keeps Arctic air contained near the poles, resulting in milder winters for the mid-latitudes. However, when the polar vortex weakens or becomes stretched, it allows frigid air to escape southward. These disruptions can be triggered by factors such as natural turbulence, high-latitude ocean warming, sea ice loss, sudden atmospheric warming, and planetary waves.

Interestingly, the current stratospheric polar vortex remains exceptionally strong, with record-high westerly winds observed in late December and early January. Despite this strength, there has been limited interaction between the stratosphere and troposphere, suggesting the cold air outbreaks this winter are not directly caused by a weakened polar vortex.

What To Expect:

Current Conditions:

  • Wednesday through Friday: Upper-level ridging will bring dry and mild conditions to Colorado, with temperatures climbing into the mid-50s on the plains by Thursday.
  • Friday Night into Saturday: A broad trough deepens over the Rockies, accompanied by an Arctic front. Snow is expected, with temperatures dropping sharply Friday afternoon. Accumulating snow is likely Friday night into Saturday, ending by evening.

Next Week:

  • Another surge of Arctic air could bring more snow Sunday night into Monday.
  • Temperatures will remain well below normal from Saturday through Tuesday, with highs in the single digits and lows below zero. Wind chills could reach -15 to -35°F, prompting potential advisories or warnings.

The long-term outlook suggests that while the polar vortex remains strong, its stretched and dynamic behavior continues to influence the rapid alternation of cold air events. These patterns are expected to persist into February.

Temperature Outlook for 1/19/25 (12Z ECMWF) Courtesy of Pivotal Weather
Temperature Outlook for 1/19/25 (12Z ECMWF) Courtesy of Pivotal Weather

Conclusion

The polar vortex is not solely to blame for the current cold air outbreak in the U.S. While it plays a significant role in shaping global weather patterns, other atmospheric phenomena like the Arctic Oscillation, North Atlantic Oscillation, and rapid PV transitions are contributing to this winter’s extreme and fluctuating weather. As the polar vortex remains a key player, monitoring its behavior and its impacts on our weather is essential.

Sources: AER, NWS, NOAA