There is a “higher than usual chance” of Europe experiencing a significant cold snap before Christmas, according to a new long-range weather forecast produced by leading international climate authorities.

The warning comes as European countries continue to fill their natural gas storages, hoping to ride out the winter heating season without access to much (or any) natural gas from Russia.

Analysts have said there should be enough gas for a normal winter, but if temperatures plunge then countries might be forced to ration access to gas, affecting industries and jobs.

The chance of a cold spell this year — most likely in December — remains “very real,” Carlo Buontempo, director of the Copernicus Climate Change Service at the European Centre for Mid-Range Weather Forecasts (ECMWF), told POLITICO.

October’s “multi-system seasonal forecast,” issued on Wednesday is based on data from the ECMWF along with six other national forecasters.

Predicting winter weather this early in the fall is fraught with uncertainty and key factors that could affect conditions — particularly in January and February — are “not yet in play,” said Buontempo. But European governments bracing for the first winter of the energy crisis should nonetheless be alert to the possibility of a pre-Christmas cold spell which would put additional pressure on the Continent’s squeezed gas supply.

“We are coming out of a warm summer. We know that winters are getting milder. So we may be inclined to think it’s going to be a mild winter and we don’t have to worry,” Buontempo said. “This may well be the case, but the forecast that we issue today and our understanding of how the climate system works lead us to suggest that actually there is still a chance of a very cold snap and, if anything, this year that chance — before Christmas — is higher than in a normal year.”

A cold snap would be linked to a so-called “blocking event” when persistent high pressure leads to “anomalous” easterly winds and colder temperatures over Europe. Currently, climactic conditions indicate that the likelihood of such an event occurring is slightly higher than usual.

Should the current La Niña weather pattern of cooler-than-average sea surface temperatures in the equatorial Pacific persist into the New Year — not something that can yet be predicted with certainty — it would typically mean a milder second half of the winter.

Another key factor in determining January and February’s weather — the polar vortex, a ring of high-speed wind surrounding the Arctic — is not yet established, making any firm predictions about this period impossible.

Buontempo said it's important for European governments to make as much use as possible of existing data on climactic conditions and likely weather patterns — not just to plan for cold snaps but also to foresee potential periods of low wind and low rainfall that could impact renewable energy production.

“We have a huge amount of free and open data available,” Buontempo said. “We need to use it properly because it has become so strategically important.”

Wednesday's forecast still contains uncertainties, and energy markets typically pay very close attention to November's long-range forecast as, by then, most of the major factors shaping weather patterns for the second part of winter are in play, Buontempo said.