Climate scientists are predicting that our winter storm seasons will become more damaging because of global warming. They predict that winter storms will become more intense, possibly more frequent, and that we are likely to see storms arriving in clusters rather than as single events (see Geofactsheet 591). Storm Eowyn, which swept through the British Isles in late January 2025, gave us a taste of what we may be facing in the future.

This blog looks at Storm Eowyn in detail, how it formed and developed, and asks the question: is the UK well enough prepared to cope not only with future storms like Eowyn, but possibly even stronger and more damaging events?

Storm Éowyn was the UK’s most powerful windstorm for over a decade. It struck western Eire on 24 January 2025, unleashing damaging winds over the British Isles, particularly over Ireland and Scotland.

Air pressure at the centre of the storm plummeted by 50 millibars in the 24 hours leading up to midnight on 24 January. That is more than twice what is required in the definition of a bomb cyclone. While it is not unusual for winter storms in this part of the world to reach bomb cyclone status, very few in recent years have shown a rate of deepening pressure comparable to that of Storm Éowyn. If Eowyn is a precursor of even more intense storms in the future, we should be concerned.

So what do we know about the storm: where it began, how it developed, and what the drivers of the storm were?

20 January

On 20 January, a significant surge of cold air swept across the eastern USA. At the same time, the North Atlantic was experiencing temperatures well above the norm for the time of year (see Image 2).

Note: The blue shading indicates lower-than-average temperatures, while the pale colours and orange shades indicate higher-than-average temperatures.

This led to the creation of steep temperature and pressure gradients over the eastern seaboard of the USA and the development of a deepening low-pressure system: an extra-tropical cyclone (ETC).

21–24 January

The deepening ETC tracked eastwards, following the approximate line of the polar front, which is the boundary between warmer sub-tropical air to the south and much colder polar air to the north. This can be estimated from Image 3.

Note 1: The red and orange shades represent warmer temperatures, while the green, blue and purple shades represent increasingly lower temperatures. The boundary between the two approximates the position of the polar front.

Note 2: The rapidly changing colour shading indicates a steep northward temperature gradient.

Note 3: Warm sub-tropical air to the south is forced to rise over the colder polar air. This causes low pressure at the surface. The steep temperature gradient forced the warm air to rise more quickly, which led to rapidly decreasing air pressure at the surface.

Note 4: The pale arrow on the diagram indicates the direction of movement of the ETC.

As the system tracked eastwards across the Atlantic, it became embedded within a fast-moving polar jet stream (the orange and red shading), which was being intensified by a very strong polar vortex (see Image 4).

Note: Notice how straight the jet stream is. This reflects a powerful zonal flow, with upper-atmosphere wind speeds reaching up to 240 mph (which incidentally reduced eastbound transatlantic flight times by approximately one hour).

The developing ETC system was picked up by the high-speed jet stream, which then drove it rapidly across the Atlantic.

As the system moved eastwards, surface air pressure dropped rapidly at its centre, triggering explosive cyclogenesis (where the central air pressure in the system drops rapidly inside a mid-latitude depression, typically deepening by at least 24 millibars in 24 hours).

24 January

Storm Eowyn made landfall over the west coast of Eire, by which time the central air pressure had dropped to 938 mb.

Images 5 and 6 show the synoptic chart and computer-generated visualisation for 23 January 2025, just prior to the arrival of the storm.

The tight concentric pattern of the isobars is typical of a severe winter storm, indicating a steep pressure gradient and high surface wind speeds. The “hook” shape formed by the fronts at the centre of the ETC is significant because it is associated with the formation of a sting jet.

Sting jets are narrow, short-lived and localised airstreams that can form towards the rear of an ETC. They descend from the mid-troposphere to the surface within some ETCs, generating intense surface winds and gusts in excess of 100 mph.

Note: To find out more about sting jets, visit the Met Office website.

• Power outages, particularly in Northern Ireland and Scotland, where over 1 million households were cut off, some for several days. At the peak of the storm, 30% of premises were without power.
• Travel disruption. Many train lines were closed and bus routes were cancelled. Some airports faced flight cancellations and delays. Road closures were widespread due to fallen trees and debris.
• Fatalities and injuries. There were at least three fatalities, primarily due to falling trees.
• Damage to infrastructure. Storm Éowyn caused significant damage to roads, sea walls and harbour infrastructure. There was also damage to forests and canals. The Canal & River Trust reported that Storm Éowyn brought high winds and torrential rain, causing fallen trees and vegetation that blocked canals and threatened wildlife.

The total cost of Storm Eowyn was estimated at over £460 million (Great Britain and Eire).

In the short run, the available options are limited.

Acceptance

Some might argue that this is exactly where we are now. But is that a viable option? Increasing storm intensities will mean that, without action, there will be more damage to property, disruption to travel, and increasing numbers of injuries and fatalities. That will lead to rapidly increasing costs and escalating insurance premiums.

Amelioration

Since we cannot prevent winter storm seasons from occurring, the next best option is to try to moderate their impacts. Here we do have options.

Research is now focusing increasingly on winter storms like Eowyn, with the aim of understanding the mechanisms involved and improving the accuracy of storm warnings.

Better and more accurate forecasts will enable more effective short-term responses to be put in place, for example evacuation, property protection, restrictions on travel, and the mobilisation of local authority support services.

Note: This assumes that local and national government have, or are developing, contingency plans to cope with projected climatic disasters (and that is a significant assumption).

Long-term planning requires that specific climate-hazard-related risks are identified and located, for example flash flooding and vulnerable coastal defences.

Work needs to be done now to develop more effective means of protecting property and infrastructure against wind hazards.

Historically, governments have been reactive in dealing with natural hazards. Planning for hazards, such as flood protection, has been based on historical data. This approach needs to change. Designing wind-proof or flood-proof structures to withstand a 25-year or 50-year event has been made increasingly irrelevant by the pace of climatic change. What happened in the past is no longer a reliable guide to the future.

Going forward, disaster planners need to think differently. That means imagining the worst possible scenario and planning for that outcome. Otherwise, in terms of disaster preparedness, we will always be playing catch-up.

The storm season lasts from early September to the end of August the following year. Storm Floris battered the UK with gusts of over 80 mph in early August, so perhaps it is not just winter storms we need to be concerned about.

For more information and discussion on the likely impact of global warming on winter storms, see Geography Factsheet 513. Winter Storms: Are They Getting Worse?