Polar Vortex: What It Is, Why It Floods the US With Cold Air, and How to Prepare

The polar vortex is not a winter storm. It is a permanent feature of the polar atmosphere, a circulation of cold air around the North Pole and South Pole that exists year round. What changes is its strength. A strong vortex traps cold air at the poles and keeps US winters relatively normal. A weak or disrupted vortex lets cold air spill south, which is when North America gets the days of -20 wind chills, frozen Texas power grids, and pipes bursting in places that have never seen pipes burst. Below is what the polar vortex actually is, what makes it weaken, and what to do when it does.

What the Polar Vortex Actually Is

The polar vortex is a low-pressure circulation of cold air around each pole. There are actually two of them on each pole, layered vertically.

The stratospheric polar vortex sits roughly 10 to 30 miles above the surface in the stratosphere. It is the one meteorologists usually mean when they say “polar vortex.” It is large, powerful, and forms every winter.

The tropospheric polar vortex sits in the lowest layer of the atmosphere, roughly tied to the polar jet stream. This is the one that affects daily weather most directly.

Both vortices are strongest in winter, weakest in summer. Both rotate counterclockwise around the North Pole when viewed from above.

Strong vs Weak: Why It Matters

A strong polar vortex is tight and fast. It locks cold air at the pole and keeps the polar jet stream relatively flat. Mid-latitudes (the US, Europe, Asia) have a normal winter.

A weak or disrupted polar vortex is slow and wavy, or split into multiple pieces. Cold air that should be locked at the pole sloshes southward. The polar jet stream becomes wavy, with deep dips that funnel Arctic air far south of normal. That is when the temperatures break records.

Sudden Stratospheric Warming (SSW)

The thing that disrupts the vortex is called a Sudden Stratospheric Warming event. The stratosphere warms by 50 to 70 degrees Fahrenheit over a few days, the vortex weakens or splits, and the disrupted state lasts for weeks. Cold-air outbreaks at the surface usually arrive 7 to 14 days after the SSW signal appears in the data. NOAA’s Climate Prediction Center monitors stratospheric temperature continuously.

Famous Polar Vortex Events

January 2014. Disrupted vortex pulled Arctic air across the eastern US. More than 200 million Americans saw subfreezing temperatures, with wind chill values below -40 across much of the upper Midwest. Ponsford, Minnesota recorded -66 degree wind chill.

January 2019. Another disrupted vortex. Chicago hit -23, the coldest reading there since 1985. More than 680 daily cold records broken in three days.

February 2021 (Winter Storm Uri). Disrupted vortex sent Arctic air deep into Texas and the Gulf Coast. Single-digit temperatures in Houston, snow in San Antonio, 9.9 million customers without power across the state, and over 200 deaths attributed directly to the storm. The Texas grid came within minutes of total failure.

January 2025. A January SSW disrupted the vortex and brought severe cold across the eastern US, forcing the presidential inauguration indoors for the first time since 1985.

“Polar Vortex” Is Often Misused

Media headlines apply “polar vortex” to any deep cold-air outbreak. Most of the time, the polar vortex itself has not moved; what reaches the surface is a lobe of cold air pinched off the disrupted vortex by a wavy jet stream. NOAA prefers the more precise terminology: “Arctic air mass” or “polar air outbreak.” But “polar vortex” is what stuck in public usage.

Connection to Arctic Warming

The Arctic is warming roughly three to four times faster than the global average. A warmer Arctic narrows the temperature contrast between the pole and mid-latitudes, which can produce a slower, wavier jet stream. Research from Judah Cohen and Jennifer Francis, among others, has linked low Arctic sea-ice winters to increased frequency of weak-vortex events. Other researchers dispute the strength of that connection. The science is still evolving; what is clear is that disrupted-vortex events have been frequent in the past decade.

How to Prepare for a Polar Vortex Outbreak

Insulate exposed pipes. Most pipe failures are in attics, garages, basements, and exterior walls. Wrap them with foam pipe insulation. Open under-sink cabinets to let warm air reach pipes against exterior walls.

Drip faucets during the worst cold. Moving water resists freezing. Drip both hot and cold from faucets on exterior walls.

HVAC service. Have the furnace inspected before winter. A failure during a polar vortex event is a true emergency.

Stock fuel for backup heat. Generator gasoline, propane, or firewood. Power outages during extreme cold are common because grids stress under demand.

Cover plants and check on livestock.

Have a warming plan. Identify a designated warm room (one room, well-insulated, blanketed off if possible). Know which neighbors and family check on you and which you check on. Cold-related deaths in Uri were largely from carbon monoxide (improper generator placement) and exposure (people without functional heat).

For symptoms to watch for in cold exposure, see our piece on hypothermia symptoms.

Frequently Asked Questions

What is the polar vortex?

A large area of low-pressure cold air circulating around each pole, present year round but strongest in winter. The phrase usually refers to the stratospheric polar vortex, 10 to 30 miles above the surface, which traps Arctic cold when strong and lets it spill southward when weak.

Why does the polar vortex make winter so cold?

When the polar vortex weakens or splits, cold air that is normally locked over the Arctic spills southward into the US, Europe, and Asia. The polar jet stream becomes wavy, funneling Arctic air far below its usual reach.

What causes the polar vortex to weaken?

Sudden Stratospheric Warming (SSW) events. The stratosphere warms 50 to 70 degrees in days, the vortex weakens or splits, and cold air outbreaks reach the surface 7 to 14 days later.

When was the most recent polar vortex event?

January 2025 saw a Sudden Stratospheric Warming and a disrupted vortex that brought severe cold across much of the eastern US, including a record-cold presidential inauguration. The 2014, 2019, and 2021 (Winter Storm Uri) events were also major.

Is the polar vortex caused by climate change?

The polar vortex itself is not new; it has existed for as long as Earth has had an atmosphere. What may be changing is how often the vortex is disrupted. Some research links Arctic warming and low sea ice to more frequent weak-vortex events. The science is still developing.

How can I prepare my home for a polar vortex?

Insulate exposed pipes, drip faucets during severe cold, service the furnace before winter, stock backup fuel for power outages, designate a warm room, and check on neighbors who may need help. Texas in 2021 showed how dangerous unprepared homes can be during prolonged cold.