Strong early signals indicate that a different, more severe winter is likely to develop in the winter of 2025/2026. weaker polar vortexA weaker polar vortex in the stratosphere usually leads to weakened or disrupted airflow below it, This increases the likelihood of a more dynamic winter pattern over the United States, Canada, and Europe. For those who prefer a colder, snowier winter, a weak polar vortex is the best option.

Polar vortex is the name for a broad winter circulation over the Northern (and Southern) Hemisphere that extends high into the atmosphere. It is divided into an upper (stratospheric) and lower (tropospheric) part, which are monitored separately, but their connection is crucial. While the upper part is more circular and symmetrical, the lower structure is much more irregular and regularly disrupted by terrain and pressure systems. The state of the polar vortex has a profound impact on our daily weather, especially in winter. Strong/stable polar vortex usually traps colder air far to the north, leading to milder conditions across most of the United States. Conversely, weak polar vortex it creates a disrupted flow pattern, making it harder for it to hold back cold air, which can now escape more freely from the polar regions into the United States or other mid-latitudes.

Three major global factors are currently emerging that create a near-perfect storm scenario for a weak polar vortex in the winter of 2025/2026:

• ENSO (El Niño Southern Oscillation) – cold anomalies or weak La Niña: We are currently in a neutral state, with stronger signals of a possible weak La Niña phenomenon during the winter of 2025/2026. Historically, a La Niña winter has a 60–75% chance of producing stratospheric warming (SSW). A typical La Niña pattern is generally more favorable for a weaker polar vortex, which means it is easier to disrupt winter weather patterns and bring colder weather and snowfall to the United States and Europe.
• QBO (Quasi-Biennial Oscillation) – stratospheric winds: This is a regular alternation of easterly and westerly winds high above the equator in the stratosphere, with the wind direction changing approximately every 17 months. Currently, a new eastern phase of QBO descends for the period 2025/2026. During the eastern QBO, the stratospheric wind profile is more favorable for the upward propagation of planetary waves from the troposphere to the stratosphere, which disrupts and weakens the polar vortex and makes it more susceptible to collapse.
• Sea ice loss: Two regions play an important role in the winter strength of the polar vortex: the Barents/Kara Sea (BKS) and the Sea of Okhotsk (SOK). Ice loss in the Barents/Kara Sea creates a weaker polar vortex, while the loss of ice in the Sea of Okhotsk is causing a stronger polar vortex. Current data show very low sea ice extent in the Barents and Kara regions and near-record highs in the Okhotsk region, which represents a “textbook situation for a weaker polar vortex” for the winter of 2025/2026. Furthermore, this effect of weakening the polar vortex by sea ice loss is much stronger during the easterly QBO forecast for 2025/2026.

All of these factors indicate an increased likelihood of an event sudden stratospheric warming (SSW) and a complete collapse of the polar vortex, which could fully unlock the potential for a cold winter. A polar vortex collapse leads to a high-pressure area over the polar regions, disrupting the jet stream and releasing cold air southward. Following a polar vortex collapse event, most of the United States and northern and central Europe are typically colder than usual, with above-average snowfall.

In summary, strong signals for a weak polar vortex in 2025/2026 increase probability of colder winter days and snowfall in the United States, Canada and parts of Europe. Spring