Why the Polar Vortex Matters for Wisconsin This Winter

By Dean Muller, Wisconsin for Environmental Justice President

For the 2025–2026 season, Wisconsin has seen a highly "unusual" winter characterized by wild swings. Here is why the polar vortex is the main culprit:

• The "Wobbly" Vortex: Usually, a strong polar vortex acts like a spinning wall, trapping freezing air at the North Pole. This winter, the vortex has been "wobbly" and disrupted by Sudden Stratospheric Warming (SSW). When it weakens, it doesn't stay over the pole; it "drips" or stretches southward.

• Alternating Cycles: This explains why Wisconsin has alternated between record warmth (like the mild temperatures seen around Christmas) and the current brutal cold snap. When the vortex is strong, we get mild Pacific air; when it collapses or "splits," it sends a direct "tongue" of Arctic air into the Great Lakes.

• The La Niña Connection: This year's weak La Niña typically brings wetter conditions to the Midwest. When that moisture meets a southward-dipping polar vortex, it leads to the heavy, "slushy" snow and ice events Wisconsin has been seeing this January.

A Visual of the Vortex

Credit: NOAA/National Weather Service. The left shows a stable vortex keeping cold air north; the right shows the wavy, disrupted pattern sending Arctic air into the U.S.

For a visual breakdown of how these air masses move, you can watch this explanation of the Polar Vortex split. This video provides a clear visual representation of how a disrupted polar vortex allows arctic air to escape the North Pole and surge into regions like Wisconsin.

This extreme weather causes havoc on our communities - and requires residents like you to foot the bill.

Sign our petition to act now so we can change this cycle and hold polluters accountable.