Winter 2025-26 outlook - mild but major uncertainties

The winter 2025–26 forecast for December, January, and February has been released. The headline calls for a milder than average season, but a significant caveat accompanies the outlook.

The UK seasonal forecast headline is for winter 2025-26 to be milder and wetter than average over the three month period.

The probability of cold conditions is expected to peak between mid-December and mid-January. However, a significant caveat accompanies this forecast, largely due to recent developments in the stratosphere as well as the underlying background signals.

Forecast considerations

The forecast was produced by looking at a number of factors, including:

• Seasonal forecast models
• Persistence patterns during recent seasons and historical analogues
• ENSO conditions
• Indian Ocean Dipole (IOD)
• Quasi-Biennial Oscillation (QBO)
• Atlantic sea surface temperatures (SSTs)
• Solar activity
• Autumnal weather patterns and the development of snow cover in Siberia

The Weather Analogue Index (WAI) which was tracked through the autumn months.

Following the trend of recent years?

Seasonal forecasting for the UK is notoriously challenging due to its location at the edge of the Atlantic. However, the multi-model consensus for Winter 2025–26 presents a fairly consistent outlook. The vast majority of long range computer models (seasonal ensembles) indicate a strong bias toward above average temperatures.

This aligns with broader climatological trends, as the past decade has predominantly favored warmer winters. Colder than average months have become increasingly rare; this year, only January fell below the 1961–90 Central England Temperature (CET) average, and even then the deviation was slight (-0.4°C). Without a specific and powerful driver to sustain cold air, the default expectation for a "modern" UK winter is mild, as well as potentially wet and windy.

Background signals: The case for cold?

Despite strong model support for mild conditions, certain background signals (known as teleconnections) historically favour colder, more blocked weather patterns.

ENSO Phase: The current state of the El Niño-Southern Oscillation (ENSO) suggests an increased likelihood of high-pressure blocking forming over the North Atlantic, especially in early winter. Should high pressure establish itself to the north or west of the UK, it would cut off the mild Atlantic flow and allow Arctic air to surge southwards.

QBO (Quasi-Biennial Oscillation): The QBO is presently in an easterly phase. Statistically, an easterly QBO weakens the stratospheric polar vortex, making it more prone to disruption. This weakening is linked to a reduction in the strength of the mild westerly jet stream, thereby increasing the chances of cold snaps reaching the UK.

The Stratospheric Wildcard

A big uncertainty in this forecast lies high above us. A Sudden Stratospheric Warming (SSW) event has recently occurred, marked by a reversal of zonal winds at the 10hPa level.

In a typical scenario, an SSW disrupts the polar vortex, and this disruption “trickles” down to the troposphere (where our weather takes place) after a lag of several weeks. This coupling often results in a negative North Atlantic Oscillation (NAO), which shifts the jet stream southward and allows cold, continental air to dominate.

Because of this recent SSW, the period from late December through mid-January carries a “red flag” for potential volatility. The atmosphere is primed for a blocking pattern; the key question is whether the troposphere will couple strongly enough with the stratosphere to sustain prolonged cold conditions.

Conclusion: The Balance of Probability

This creates a complex battleground: a warming climate and mild model forecasts versus specific atmospheric factors (QBO, ENSO, SSW) that tend to favour colder conditions.

Overall, our assessment is that although the ingredients for a significant mid winter cold spell exist, they are unlikely to dominate. We expect the possibility of colder spells, but the prevailing signal points toward a season characterised by variability and average to mild temperatures. The precipitation signal is less clearly defined, but we consider it more likely that rainfall across the UK will be above rather than below the average.

TWO winter 2025-26 forecast