A 3D flyby
Winter's hardest cold snaps begin with three things acting together: a river of wind at the top of the weather layer, a ring of wind far above it, and the temperature of the Pacific Ocean. This tour shows how they connect.
Nov 9 The polar vortex is at a record low for the date Watch the video (1 min 59 s)Stop 1 · The layers
The atmosphere comes in layers. Weather happens in the lowest one, the troposphere. The polar vortex spins in the next one up, the stratosphere. This slice runs from the equator to the North Pole.
Heights are stretched here. To scale, all four layers shown would be a film too thin to see.
Layers of the atmosphereStop 2 · Troposphere
Near the top of the weather layer, a river of wind circles the planet from west to east at an average of about 110 mph. It forms where cold polar air meets warmer air, and it marks the boundary between them. Storms travel along it.
How the jet stream worksStop 3 · Stratosphere
Far above the jet stream, 10 to 30 miles up, a ring of westerly wind forms over the pole every winter. It circles a pool of cold air, and while it spins fast and tight, that air stays put. You are looking down on the North Pole.
The polar vortex in depthStop 4 · Sudden stratospheric warming
Giant waves in the atmosphere, set off by mountains and by the contrast between land and sea, travel upward and break against the vortex. The air over the pole can warm by up to 50 °C in a couple of days. The vortex slows, slides off the pole, or splits in two.
Sudden stratospheric warmingStop 5 · Back at the surface
Over the next two to six weeks the change can work its way down. The jet stream often buckles into deep waves, and Arctic air pours south through the dips.
It does not happen every time. A breakdown loads the dice for cold. It does not guarantee it.
What it means on the groundStop 6 · Tropical Pacific
In El Niño the trade winds weaken and warm water spreads east along the equator. The Pacific jet stream shifts south and runs straighter across the country. Storms follow it, so the southern United States tends to be wetter. Less cold air comes down from Canada, so the north tends to be warmer.
Trade winds blow west along the equator and pile warm water up near Indonesia, while cold water rises off South America. Roughly half of all years look like this.
In La Niña the trade winds blow harder than usual and the eastern Pacific cools. The jet stream swings north over the Pacific, then turns wavy across North America. Its dips tend to bring cold air into the north, while storms pass by the southern United States, which tends to be warmer and drier.
El Niño and La Niña explainedStop 7 · The result
A buckled jet stream is where the trouble starts. Cold air plunges south in the dips while warm, moist air is drawn north ahead of them, and storms form where the two meet: blizzards and nor'easters on the cold side, tornado outbreaks on the warm side. Atmospheric rivers carry tropical moisture to the West Coast.
Severe weather, type by typeYour turn
Drag the globe to look around, and switch the pieces on and off to see how they move together.
Polar vortexDrag to look around
Heights not to scale
Video · 1 min 59 s
The polar vortex, from the ground up: the whole story, narrated, with captions you can switch on.
Right now · updated automatically
This site follows two signals: the wind around the pole, far overhead, and the temperature of the tropical Pacific. The readings below come from NASA and NOAA and update on their own.
Stratosphere · NASA
On November 9, 2026 the wind circling the pole was 1.2 meters per second (3 mph) from the west. The average for that date is 28.4 (64 mph). NASA's forecast data shows a reversal from November 10 to 12, 2026, which the analysis has not yet confirmed.
Pacific Ocean · NOAA
NOAA's alert status is El Niño Advisory, set on November 12, 2026. NOAA's official index for August to October 2026 is +1.97 °C. NOAA's summary: "El Niño continues to strengthen, with a strong-to-very strong El Niño likely through January-March 2027 (remaining greater than a 79% chance)."
Warnings in effect now, and today's storm outlook
Winter 2026-27 · written November 10, 2026
In November 2026 a strong El Niño tilted the odds toward a mild winter across the northern United States, and an unusually early disruption of the polar vortex tilted them toward cold outbreaks. NOAA's forecasters wrote that some of the potential impacts of the disruption "compete with those from El Nino."1
The wind around the pole had dropped from about 50 mph in late October to under 1 mph on November 5, the weakest for the date in NASA's record.2 A full reversal was forecast but not yet measured. A confirmed one would be the earliest major breakdown since records began in 1958.3 In the Pacific, NOAA expected a "strong-to-very strong El Niño" through January to March 2027 and said chances were high for a historic event, stronger than any since 1950.4 Its winter outlook favored a warmer north and a wetter southern tier.5
"As a weather fan, this is a big event because it's so unprecedented. It's a lot of excitement. Everybody's hair is on fire in the climate or meteorologist community."
Cohen also told the magazine how open the outcome was: it could be a "minor" event that "everybody will forget about," or "it will be major, and then it'll go in the record books."6
This note is not updated automatically. The readings above are. Neither is a forecast: for the forecast where you live, use your national weather service.
The short version
El Niño and La Niña move the Pacific jet stream, and El Niño tends to send more wave energy up toward the vortex.78
Especially strong waves break upward into the stratosphere and knock the polar vortex off balance.9
When the vortex weakens, shifts or splits, the jet stream below often turns extremely wavy.9
The waves move slowly and sometimes stall, so cold, storms or heat can sit over one region for days.10
Each link shifts the odds. None is a guarantee: plenty of Arctic outbreaks happen with no help from the polar vortex.9
The guide
01
Five layers, and why the temperature reverses at every boundary.
Read
02
What it is, how a sudden stratospheric warming breaks it, and what follows.
Read
03
Ridges, troughs, blocking, and why it is not the same thing as the vortex.
Read
04
How the Pacific swings, how NOAA measures it, and what each phase does to winter.
Read
05
Arctic outbreaks, blizzards, bomb cyclones, tornadoes, atmospheric rivers and heat domes.
Read
06
Every term on the site in a sentence or two.
Look up
About this guide
Every number on this site is tied to a source you can open: NOAA, NASA, the UK Met Office, the World Meteorological Organization, and peer-reviewed research. Where good sources disagree, the page gives the range. Where the science is unsettled, as it is on whether a warming Arctic is changing the jet stream, the page says so and shows both sides.
The 3D flyby and the diagrams are schematic. They show how the pieces fit, not the weather on any particular day.