It was 82 years ago that General Eisenhower’s chief meteorologist issued one of the most important weather forecasts in history.
D-Day speech called on World War II allies to save the world
More than 70 years ago, General Eisenhower addressed thousands of World War II Allied soldiers before storming Nazi forces on the beaches of Normandy, France.
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Should I go or not?
June 2026 marks 82 years since Col. James Martin Staggroup, General Dwight D. Eisenhower’s chief meteorologist, issued one of the most important weather predictions in history. Over the objections of his colleagues, he advised Ike to postpone the Normandy landings by one day from June 5 to June 6, 1944, due to unstable weather conditions.
This momentous decision is the subject of the new film Pressure, starring Brendan Fraser as Ike, now in theaters. The real-life D-Day was a herculean effort to take back key areas of Europe from the Nazis and change the course of the most horrific war the world had ever seen.
Stagg (who was actually a geophysicist by training) and his fellow British and American meteorologists worked without any of the technology and equipment that today’s forecasters take for granted, such as satellites, weather radar, computer modeling, or real-time communications.
Relying primarily on ground observations by military and civilian weather observers in the British Isles and Western Europe, as well as a small number of military observers at sea, it was impractical to predict the weather at the time more than a day or two in advance.
Additionally, weather forecasts in the UK and Europe were much more complex than those in the United States, especially before the advent of satellites. In the United States, even in that era, weather systems could be tracked for several days after they reached the West Coast and moved east, whereas European forecasters often operated “blindly” across the western sky.
The D-Day Forecast states that predicting the precise timing, course, and strength of these storms has placed Captain Stagg and his colleagues under almost unimaginable pressures and conflicts, with the fate of the war and perhaps the world at stake.
In the days leading up to D-Day, meteorologists were troubled by the parade of storms that would sweep across the Atlantic and into the British Isles, any of which would stir up the treacherous waters of the English Channel where the fleet was assembled and provide unwelcome cloud cover for the Normandy raids.
The invasion was originally scheduled for the morning of June 5, but the weather was so bad that Stagg advised Ike to postpone it for a day, despite the protests of his fellow meteorologists who thought the weather was good enough for the mission.
Why was weather forecasting so important to the invasion?
According to meteorologist and weather historian Sean Potter, like many military operations, the success of the Normandy landings on D-Day was largely dependent on the weather. But D-Day was no ordinary military operation. Each component of the invasion (navy, air force, ground forces) had its own weather requirements.
“For example, a forecast that implies ideal conditions for bombers may not take into account the need for a seaborne invasion,” Potter told USA TODAY via email. “Invasions also depended on a limited combination of tides, moonlight, cloud cover, wind, and sea conditions and occurred only during limited opportunities.”
How difficult was forecasting using 1940s technology? How does it compare to forecasting today?
While weather forecasting has seen significant improvements in the two decades leading up to D-Day, particularly with the development of polar front theory about how storms develop, there are still limitations that make predicting D-Day a real challenge, Potter explained.
“Today’s forecasters utilize advanced technology, including radar, satellites, and other numerical weather forecasts, to make accurate predictions. None of this was available to D-Day forecasters,” he added.
Another challenge was that one of the three Allied forecast teams that contributed to the D-Day forecast, led by American Irving Crick, relied primarily on a technique known as analog forecasting, which compared immediate weather conditions to similar scenarios in the past to determine what would happen.
“By 1944, analog forecasting was viewed with skepticism by many meteorologists and was being largely replaced by other, more modern methods,” Potter said.
Looking back, how accurate were your predictions?
Forecasters eventually identified a critical break in the weather that made an invasion possible, but conditions remained rough, far from ideal, and not entirely as expected.
Potter explains: A 2020 paper published in the Proceedings of the American Weather Society suggests that the D-Day forecast was essentially “right for the wrong reasons.”
The study’s author, Swedish meteorologist Anders Persson, reviewed transcripts of telephone conversations between coalition forecast teams and concluded that forecasters had accurately predicted the weather break on June 6, but had misunderstood why it would occur. They believed that the storm system that delayed the invasion would recede and be replaced by higher pressure and improving conditions.
Instead, the storm remained over the invasion area but weakened slightly, providing weather that was still acceptable for Eisenhower’s decision to march, albeit slightly.
How accurately does the new film depict the events of the time?
Overall, Potter said the film is a very accurate depiction of the role weather played in planning D-Day and the challenges forecasters faced in predicting it.
“Some liberties were taken, such as suggesting that Eisenhower’s chief weather advisor, James Stagg (played by Andrew Scott), was not involved in the D-Day forecast until days before the invasion, when in fact he was involved for months. It also likely over-dramatizes the tensions and conflicts between Stagg and his American counterpart Irving Crick,” Potter said.
“While there were disagreements, they were largely kept to a technicality. One of the things this film does very well is convey the sense of uncertainty that Stagg had in the weather forecasts he presented to Eisenhower. Understanding the uncertainty in weather forecasts is still an important part of making decisions when weather is a factor.”
What would have happened if they had delayed D-Day?
As mentioned above, although far from perfect, the weather on the morning of June 6 was sufficient for a successful invasion.
If the mission had not ended on June 6th, the next period would have been two full weeks later, with suitable tides and moonlight. Two weeks later, the invasion would have failed due to a completely unexpected strong wind.
Author John Ross wrote in his book D-Day Forecast that if the invasion had failed, the secret of when and where Allied forces would land would have been lost, victory in Europe would have been delayed by a year, and the Soviet Union might have taken control of the continent.
Years later, President-elect John F. Kennedy, on his way to the Capitol for his inauguration, asked President Eisenhower why the Normandy landings were so successful.
Ike’s answer: “Because we had better meteorologists than the Germans!”
Contributors: Phaedra Trethan and Janet Loehrke
Doyle Rice is a national correspondent for USA TODAY, focusing on weather and climate.
