The main medium and long-scale weather prediction models indicate for mid-January 2026 a new episode of stratospheric warming over the Arctic. This sharp rise in temperatures in the upper atmosphere could significantly alter winter circulation in the Northern Hemisphere for several weeks.
Joint simulations of centers such as ECMWF and GFS point to a clear weakening of the stratospheric polar vortexThe large circulation that acts as a "wall" against frigid Arctic air. When this structure is distorted or stretched, the probability increases that very cold air masses will move towards mid-latitudes, affecting a large part of Europe, including Spain, and North America with episodes of more intense and temporarily persistent cold.
What is stratospheric warming and why does it matter?
In winter, a huge vortex of very strong winds forms over the North Pole, extending from the troposphere to the stratosphere. The polar vortex acts as a gigantic barrier which traps the coldest Arctic air near high latitudes. As long as the vortex remains compact and symmetrical, regions of Western and Central Europe tend to have relatively mild winters, or at least without continuous extreme cold spells.
Un stratospheric warming It is an episode in which, in just a few days, the temperature in the polar stratosphere can rise between 15 and 30 °C above normal. This warming is linked to the upward propagation of large planetary waves (Rossby waves) from the troposphere. This upward energy alters the stratospheric circulation, deforms the vortex, and can even temporarily reverse the prevailing winds from west to east.
When the disturbance is intense enough, it is referred to as sudden stratospheric warming (SSW)This formal threshold of total wind reversal is not always reached, but even in more "moderate" versions, the impact can be remarkable: the vortex stretches, shifts, or fragments into several lobes, facilitating genuine leaks of polar air towards North America, Europe, or Asia.
What's relevant for the surface is that these changes above don't stay there. The signal generated in the stratosphere descends to increasingly lower levels. in a process that usually lasts between one and three weeks. As the disturbance couples with the troposphere, the polar jet stream reorganizes and pressure patterns change, resulting in periods of intense cold, persistent anticyclonic blocking, and a greater likelihood of snowstorms.
Signs of the January 2026 event in the models
The latest high-resolution model outputs identify significant stratospheric warming over the Arctic towards the second week of JanuaryPositive temperature anomalies between 10 and 30 hPa in the middle and upper stratosphere reach values of around 20 to 30 °C above the climatological average in the polar dome.
Zonal wind analyses show a progressive deceleration of the circumpolar circulation At levels such as 10 hPa, the vortex tends to lose its almost circular shape, adopting a more elongated appearance. This deformation is usually associated with a stretching of the vortex towards North America on one side and towards Eurasia on the other, which favors the escape of very cold air from the polar ice cap.
According to the ECMWF and GFS datasets, The peak of the warming would occur approximately between January 12 and 15.During that interval, most members of the ensemble agree on a marked increase in stratospheric pressure over the North Pacific and Alaska, shifting the center of the vortex towards eastern Canada and areas of the Eurasian Arctic.
Although some scenarios do not reach a "textbook" SSW with complete wind reversal, the disturbance is considered sufficient to alter hemispheric circulationThe downward signal is already appearing in the 50 hPa and 100 hPa forecasts, with a clear reduction in zonal wind speeds and a geopotential pattern indicative of a stretched and partially split vortex.
From the Arctic to the surface: how the signal drops
Once high-level heating is triggered, models indicate a downward propagation process relatively classic: first a zone of high stratospheric pressure consolidates over the northeast Pacific and Alaska, while the core of the vortex is displaced towards eastern Canada and, to a lesser extent, towards the Eurasian sector of the Arctic.
In the lower stratosphere, the signal translates into a gradual decrease in westerly winds and in a reorganization of the geopotential height pattern. This process usually takes about two weeks, so the main surface effects are concentrated between the second half of January and the first part of February.
As the signal reaches the troposphere, Anticyclonic blocking patterns are strengthening at high latitudesEspecially in the Greenland and North Atlantic region, while low-pressure centers deepen in mid and low latitudes. This combination opens up veritable "corridors" for Arctic air, which can slide southward in successive waves.
In this scenario, joint predictions point to an increased probability of episodes of intense cold and winter instability in large regions of the northern hemisphere, with special attention to central and eastern Europe, Scandinavia, the British Isles and large areas of eastern North America.
European dynamics under a weakened vortex
In the European case, the models draw fairly consistent patterns. Recurring high-pressure blocking systems over Greenland and the North AtlanticThis type of pattern, closely associated with negative phases of the North Atlantic Oscillation (NAO-), redirects the usual westerly flow to more southerly trajectories and favors the arrival of continental polar air.
Temperature anomaly projections suggest that Scandinavia, the British Isles and much of central and eastern Europe Temperatures could drop by 4 to 6°C from the average during the second half of January. This would create conditions favorable for frequent snowfall, even at relatively low elevations, in Nordic countries, the Baltic region, and inland areas of the continent.
At the same time, the ECMWF group points out increased storm activity in the Mediterranean regionThese low-pressure systems would transport humid air towards the Alps, the Balkans, and the Iberian Peninsula. Combined with cold air masses from the north and northeast, the probability of snow in mountain ranges such as the Alps, the Carpathians, the Pyrenees, and the Iberian System increases significantly.
Negative NAO, AO and blockages: the winter cocktail
The results of the seasonal and overall prediction models point to a probable negative phase of the NAO (North Atlantic Oscillation) Following the peak of stratospheric warming, this configuration is associated with higher than normal pressures over Greenland and lower pressures over the mid-Atlantic and southern Europe.
In parallel, indicators such as the AOs (Arctic Oscillation) These values would tend toward neutral or negative values, consistent with a weakened polar vortex and less zonal circulation. Historically, these patterns have been linked to winters with a higher incidence of cold outbreaks in Europe and North America, although they do not necessarily imply continuous cold, but rather alternating phases.
The combination of negative NAO, low AO values, and recurrent blockades over Greenland It favors the polar air to emerge in several waves. towards the European continent, instead of remaining confined over the ocean. This increases the likelihood of repeated cold periods, interspersed with brief, milder breaks when the Atlantic circulation manages to break through.
The expected result, according to the historical analogies used by different research centers, is a potentially colder than usual second half of January in many European countries, with impacts on energy consumption, mobility and agricultural planning, especially in Eastern and Central Europe.
The role of La Niña, the QBO and Siberian snow
The stratospheric warming of January 2026 does not occur in a vacuum: it relies on several factors of planetary scale which help to understand why the atmosphere is so predisposed to this type of episode this winter.
On one hand, one observes a La Niña of weak intensitywith cold anomalies at the ocean surface of around 0,5 to 1 °C. These sea temperature patterns modify the tropical circulation and tend to intensify planetary waves that propagate towards high latitudes, facilitating the transfer of energy to the polar stratosphere.
This is in addition to a phase negative of the Quasi-Biennial Oscillation (QBO)with easterly winds in the equatorial stratosphere. This configuration has been linked in several studies to less stability of the polar vortex and a greater probability of stratospheric warming during the boreal winter.
Another key ingredient is the extensive snow cover in Siberia observed in the fall of 2025, which in some analyses appears above average. A wider snow cover in that region favors the reflection of energy towards the atmosphere, contributing to strengthening the large-scale waves that disturb the stratospheric circulation and, with it, weaken the vortex in the following months.
The combination of these factors—weak La Niña, eastern QBO, and abundant Siberian snow—fits with a pattern of years in which the risk of SSW or strong stratospheric warming increasesThis is supported by long-run studies and analyses of analogies from past winters.
Potential weather impacts on Europe and Spain
If the majority model scenario is confirmed, the northern hemisphere would face a higher probability of repeated arctic air intrusions until the end of January, and possibly with repercussions into early February. Europe would be one of the regions most exposed to these changes, with notable variations between subregions.
In the north of the continent, Scandinavia and the Baltic countries These areas are shaping up to be the ones with the most pronounced cold fronts and the most frequent snowfall, even in flatlands. The British Isles, due to their location on the Atlantic coast, could experience alternating periods of very cold and dry weather under continental flow with brief windows of warmer, wetter weather when the Atlantic jet stream temporarily prevails.
Central and Eastern Europe, from Germany and Poland to the BalkansThis region would be favored for significant snow accumulations in several waves, with frequent nighttime frosts and a risk of icy conditions in urban areas. The persistence of these conditions would have implications for transportation, energy demand, and, to a lesser extent, certain winter crops.
In the Iberian Peninsula, the signal is less extreme but not negligible. The overall scenarios suggest incursions of continental cold air and maritime polar air. slipping around the eastern flank of the Atlantic blockades, which opens the door to snow episodes in mountain systems such as the Pyrenees, Cantabrian Mountains, Iberian System and Betic Mountains, in addition to widespread frosts in the interior of the peninsula during some periods.
Prediction and confidence levels
The prediction centers emphasize that, although the The stratospheric signal is relatively well definedThe exact way this will translate into surface time remains subject to uncertainty. The ECMWF and GFS ensembles show high agreement regarding vortex stretching and weakening, but disagree on how quickly the vortex might re-establish itself and on the precise location of the blocking maxima.
In probabilistic terms, some internal studies indicate support of around 60-70% for scenarios with a negative NAO and repeated cold weather in large regions of Europe, compared to 30-40% of scenarios in which the recovery of the vortex would be faster and the Atlantic jet stream would prevail again before the end of the month.
This sensitivity is largely due to small displacements in the position of the high and low pressure centers At high latitudes, a blocking anticyclone centered over Greenland channels cold air masses very differently than one located further west or toward the Canadian Arctic. Therefore, it is emphasized that weekly updates will be key to refining the intensity, duration, and spatial distribution of cold spells.
In any case, the starting point after stratospheric warming invites us to Do not rule out sudden changes in weather in a few days, with corridors of very cold air capable of reaching much of Europe and, to a lesser extent, the Iberian Peninsula, interspersed with milder phases when the pattern partially relaxes.
All indications suggest that the stratospheric warming of January 2026 will be a major factor in the evolution of the Northern Hemisphere winter, at least for a few weeks. With a weakened stratospheric polar vortex, frequent blocking patterns around Greenland, and an unusual combination of planetary-scale factors, Europe is heading towards a potentially colder, more variable winter with more likely than normal episodes of snow and frost.This is a scenario that meteorological services will closely monitor in order to adjust short-term warnings and forecasts as the stratospheric signal finishes merging with the atmosphere we experience on the surface.
