The polar vortex is often talked about whenever a cold spell strikeswhile in realityit’s an atmospheric feature that exists throughout the entire winter season. Wisconsin is occasionally impacted by the Arctic polar vortexwhich is centered over the North Polethough there is an Antarctic polar vortex over the South Pole. In this discussionwe’ll just focus on the Arctic polar vortex.
Vortex vs. Jet Stream: What’s the Difference?
The polar vortex refers to a center of low pressure that swirls in the stratosphere (about 10 to 30 miles above the ground) around the North Pole during the winter. Inside the vortex is extremely cold Arctic air. The colder the air in the vortexthe faster the vortex tends to spin.
The polar jet stream is a river of wind that flows from west to east about five to nine miles above the ground. The polar jet stream is typically north of Wisconsin and helps keep the Arctic air contained near the North Pole.
When the Vortex is Stable…
When the polar vortex is stable and strongthe polar jet stream usually stays strong as well. This traps the icy air up northrestricting its impact on Wisconsin. Think of it like swirling a lasso: when you spin it quicklyit creates a nearly perfect circle. In this casethe jet stream is lassoing the cold air.
When the Vortex is Unstable…
Sometimes temperatures high up in the atmosphere warm up suddenlycausing the polar vortex to weaken. This is called sudden stratospheric warming. During these eventsthe vortex slows downoften shifts away from the North Poleand can even split in two. As a resultthe polar jet stream may also become unstableand allow Arctic air to slip south — sometimes into Wisconsin. Bringing back the lasso analogywhen it’s spun slowlythe rope becomes wavy.
The Coldest of the Cold
Arctic pools of air are typically responsible for Wisconsin’s most extreme cold conditions. An outbreak of Arctic air in February 1996 resulted in Wisconsin’s all-time coldest temperature on record: minus 55 degrees Fahrenheit in Couderay (Sawyer County).
In more recent yearsthe Arctic blasts of January 2014 and 2019 stand out in memory. Two bouts of arctic air struck in January 2014dropping temperatures in Wisconsin to 30 degrees below zero and wind chills to 40 below!
A similar temperature plunge was seen at the end of January 2019but stronger winds made for even colder wind chills. Feel-like temperatures of 50 below zero were common across the state. A minus 60 degree report from Menomonie (Dunn County) made for Wisconsin’s coldest wind chill on record.
Bracing For the Cold
Even though Wisconsin is a cold-weather stateit’s important not to underestimate the dangers of the cold. Frigid air from the Arctic can cause frostbite and hypothermia that can turn deadly.
According to the Wisconsin Department of Health Servicesan average of 60 cold-related deaths occurred in the state each winter since 2015. Stay inside if temperatures reach dangerous levels. Always dress for the cold when you do have to venture outand have an emergency kit ready just in case.
This is a product of the Wisconsin State Climatology Office. For questions and commentsplease contact us by email ([email protected]) or phone (608-263-2374).