AI D-Day weather forecast falters under pressure
03 September 2026
Today's best weather computers would still have struggled to accurately predict the weather for the D-Day landings, University of Reading research shows.
The new research, accepted in the journal Weather ahead of the release of D-Day blockbuster Pressure, used AI models to produce 50 different forecasts of the storm that famously pushed back the Allies’ invasion of Normandy in June 1944.
The researchers checked how confident the AI model was about the weather Group Captain James Stagg had to forecast on 5 and 6 June. For 5 June, the day originally planned for the invasion, the model got the storm's position right and correctly predicted poor conditions over Normandy, matching Stagg's own analysis. For 6 June, the model predicted the storm would move towards Norway, bringing calmer weather, albeit much quicker than what really happened.
Professor Andrew Charlton-Perez, lead author of the study at the University of Reading, said: "Captain James Stagg had one of the hardest jobs in history. Get the forecast wrong, the invasion could have failed and the Second World War could have been lost.
“Some Allied meteorologists were insistent the weather would be fine for the invasion to take place as planned on 5 June, after weeks of hot weather. Our research shows Stagg would likely have defied his colleagues and made the same call to delay if he had the AI forecast to support him. The AI pointed to a real risk of dangerous winds on 5 June, enough to justify delaying the invasion by a day.
“The AI incorrectly predicted 6 June would be much calm and clearer than it really was, as soldiers faced more treacherous weather. Captain Stagg believed the conditions were fair enough on 6 June, leading to Eisenhower to give his famous order, "OK, we'll go."
“AI weather forecasts can process huge amounts of data in seconds, but they can still make mistakes. Having a trained meteorologist to make sense of all of the forecast data and make forecasts based on their knowledge and experience remains just as critical today as it was for the D-Day landings."
Where the model went wrong
The extraordinary story of how Captain James Stagg had to determine if the weather would be good enough to let 160,000 troops cross the Channel and storm the beaches of Normandy on 5 June is now the subject of a major Hollywood film called Pressure starring Andrew Scott as Stagg and Brendan Fraser as Eisenhower.
In the film, Stagg has to balance his advice between different forecasting teams who disagree about how a storm in the North Sea will affect the invasion.
Researchers compared the model against what actually happened over the Channel and the Normandy beaches, using weather records from the Copernicus Climate Change Service.
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The model showed the storm clearing away from Britain too quickly on the 6th June. This wrongly suggested that 6 June would be calm and clear, when on the day of the invasion some of the invading forces faced high winds and stormy seas.
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Underneath that overall confidence, the wind numbers told a different story. The model still showed a 30% chance the wind would break the safety limit for landing craft on 6 June, a real risk hidden behind its reassuring overall picture.
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The model also predicted clearer skies than actually happened on 6 June, adding to the false sense that conditions would be fine.
Filling in the gaps
Weather records from 1944 were limited, so the researchers also compare the forecasts with new paper weather logs for the Faroe Islands recently found in an archive at the Met Office. These islands sit close to the path the storm took on its way past Britain, so the readings kept there in 1944 capture the storm at a point the main records miss.
Turning these old paper logs into digital data made it possible to check the storm's strength more closely and showed it may have been slightly stronger than current reconstructions suggest. Digitising more of these historic logs from archives across Europe could let scientists test storms like this one even more precisely in future.
Pressure releases in UK cinemas on Wednesday, 9 September.
Notes to editors:
Professor Andrew Charlton-Perez is available for interview. Contact the University of Reading Press Office on 0118 378 5757 or pressoffice@reading.ac.uk
Images via Studio Canal.
Full reference: Charlton-Perez, A., Burt, S., Cloke, H., Hawkins, E., Lee, R., Simmons, A. and Volonte, A. (2026), Pressure: reimagining the D-Day forecast through machine learning. Weather, 81: 284-293. https://doi.org/10.1002/wea.70123
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