– One Weather Forecast Changed
the Course of WWII –
by Meilan Solly | Smithsonian Magazine | May 28, 2026
A new movie starring Andrew Scott and Brendan Fraser dramatizes the tense 72 hours before the Allied invasion of Normandy, revealing how meteorology helped determine Operation Overlord’s success.
Here’s the real story.
In the spring of 1944, with Germany in control of much of continental Europe, the Allies pursued a long-anticipated path to victory: forcing the Nazis to fight a two-front war. From the east, the Soviets advanced on Berlin. Meanwhile, Britain, the United States and Canada sought to gain a foothold in France. To do that, they planned the largest amphibious invasion in human history—an event now known as D-Day. The success of this campaign relied heavily on the weather.
During a late April training run for the assault, tens of thousands of Allied troops had stormed a beach on England’s southwestern coast. Trouble dogged the exercise from the start. Friendly fire caused multiple casualties on April 27; the next day, German warships attacked one of the convoys transporting soldiers to shore. Approximately 639 men died as a result of Exercise Tiger, with some even drowning or succumbing to hypothermia while awaiting rescue after abandoning ship. The rehearsal was an unmitigated disaster.
Exercise Tiger serves as the opening scene of Pressure, a new World War II drama that explores what some might credibly see as a footnote of Operation Overlord: the weather forecast for the invasion. In the film, General Dwight D. Eisenhower (played by Brendan Fraser) surveys the devastation wrought by the rehearsal before letting out a scream of frustration.
As director Anthony Maras tells Smithsonian magazine, this moment “anchors the vulnerability and the doubt that Eisenhower goes through … which is as simple as this: If we get something wrong, and it might just be something very minor, it could lead to utter catastrophe.”
That fear undergirds the characters’ actions in Pressure, from Eisenhower himself to the general’s chief meteorological adviser, James Martin Stagg (Andrew Scott), who is tasked with presenting a forecast that will determine the timing of D-Day—and perhaps even the outcome of the war in Europe. As Stagg weighs possible scenarios for June 5, the day originally planned for the invasion, he must contend with competing claims made by American meteorologist Irving P. Krick (Chris Messina), who outlines a much milder forecast.
Unlike many World War II movies and television shows, Pressure has no “explicit antagonist on screen,” Maras says. Instead, “you’ve got a group of people who all want the same thing. They want to win. They want to keep their men safe. And they want as few casualties as possible.” Alluding to the film’s title, the director adds, “It ultimately amounts to this really high-pressure environment where everyone knows what failure looks like, and that is blood, and that is death and that is destruction. They don’t want that.”
Here’s what you need to know about the real history behind Pressure ahead of the film’s arrival in theaters across the United States on May 29.
The Making of Pressure
Pressure is based on a 2014 play of the same name by English actor and playwright David Haig, who also co-wrote the film’s script with Maras. Haig first learned about Stagg while researching potential subjects for a play “about an unsung Scots hero.”
Maras, who previously directed the 2018 thriller Hotel Mumbai, says he was drawn to Pressure after learning “that world history was decided, in many ways, by one huge decision that rested on something that no one would even necessarily think about, which was, ‘Are we going to have a storm or not?’” As Eisenhower says in the film, “The fate of the war hinges on this. There’s only one imponderable left. I need a forecast.”
Pressure takes place over three tense days in June 1944. Allied military leaders, including Eisenhower and British Field Marshal Bernard Montgomery (Damian Lewis), gather at Southwick House in England to discuss the final preparations for Operation Overlord, the overarching name for the invasion of Normandy.
In the film’s telling, Stagg is a late arrival to the meteorological team who immediately clashes with the more congenial Krick. While Krick assures Eisenhower that June 5 will be calm and sunny, Stagg bluntly asserts that in Northern Europe, any forecast beyond 24 hours is long-term and therefore of low reliability. Much of Pressure’s tension comes from these contrasting opinions, which Eisenhower must weigh against the demands of the pending invasion.
When Haig was researching the play, he found himself captivated by Eisenhower’s relationships with both Stagg and Kay Summersby (Kerry Condon), the general’s wartime secretary, driver and rumored lover. In Pressure, Summersby acts a confidante for Stagg and Eisenhower, protecting the former from the latter’s fierce temper.
In truth, evidence of a friendship between Summersby and Stagg is limited, although the pair likely crossed paths through their work. Their imagined dynamic is one of the biggest differences between Pressure and the historical events that inspired it. Another is the compression of the timeline to just 72 hours. The real Stagg was appointed chief meteorologist of the Allied forces in Europe in November 1943, so he was well acquainted with both Krick and Eisenhower by the time of the invasion.
Although the film portrays Eisenhower and Stagg’s relationship as highly contentious, John E. Ross, author of The Forecast for D-Day and the Weatherman Behind Ike’s Greatest Gamble, suggests otherwise. “Both were so well aware of the gravity of the moment that they behaved with utmost professionalism,” he tells Smithsonian.
According to Stagg’s 1971 memoir, Forecast for Overlord, June 6, 1944, Eisenhower often stopped by his office to “ask about the weather for the rest of the day” in the weeks before D-Day. Through these conversations, “Eisenhower developed a sense that he could really trust what Stagg had to say, and that was absolutely critical,” Ross says.
James Stagg versus Irving P. Krick
Described by Eisenhower as a “dour but canny Scot,” Stagg wasn’t the obvious choice to lead the D-Day forecasting team. A geophysicist by trade, his main forecasting experience was a two-year stint in Iraq in the 1930s. Stagg himself was surprised by the appointment, expecting the role to go to a colleague in the Meteorological Office (more commonly abbreviated as the Met Office). But he had apparently impressed the right people by ensuring that the weather services for the Royal Air Force and the British Army “worked effectively together,” as he wrote in his memoir.
Stagg approached the job with trepidation, in no small part because he knew that he would need to consult with multiple forecasting teams. As Stagg told the office’s director before finding out that he’d been chosen for the role, he failed to understand why the head meteorologist “cannot be allowed to make his own forecast, consulting whom he wishes or no one, as he chooses.”
While Pressure suggests that Stagg and Krick led two conflicting teams of meteorologists, in actuality, three independent bureaus reported to Stagg: the U.S. Army Air Forces, led by Krick and headquartered at Widewing in southwest London; the Met Office, which worked out of a base in Dunstable, north of London; and the Admiralty, operating under the auspices of the Royal Navy. Each center offered a forecast to Stagg, who drew on his own expertise to synthesize the data provided, then communicated this information to Eisenhower and the other Allied commanders.
Pressure’s depiction of the tense relationship between Stagg and Krick is relatively true to history, with the pair holding “completely opposing views on weather forecasting,” Ross says. Stagg “was a consummate scientist, and he really wasn’t at all interested in rank or aspirations after the war,” Ross explains. “His job was simply to come up with the best possible forecast.”
Krick, in contrast, was a natural salesman with a side hustle advising Hollywood studios. (He correctly predicted calm weather on the day that the crew of Gone With the Wind filmed the burning of Atlanta.) Krick and his American colleagues relied on analog forecasting, a method in which meteorologists look to the past to find answers about the future, poring over weather maps from previous years in search of patterns. As Ross writes in his book, “Krick held that if today’s weather map matched closely to one from the past that, generally speaking, the weather that occurred on the day following the historic chart would be very much like that which could be expected for tomorrow.”
Andrew Charlton-Perez, a meteorologist at the University of Reading in England, says that the analog method Krick used “is essentially what the new generation of machine-learning weather forecasting does.” To generate the forecast a person might find on their cellphone today, he tells Smithsonian, an artificial intelligence tool “looks at all of the previous conditions, and then it looks at the relationships between the variables—what happens 6 hours from now, 12 hours from now—and then it uses the neural network within the model to predict what might happen in the future.”
The British teams advising Stagg took a different approach to forecasting, basing their predictions on “a really evolving knowledge of atmospheric physics” influenced by the Bergen school of meteorology, Ross tells Smithsonian. As the New York Times explained in 2025, these bureaus “relied on hand-drawn charts, observational data and newer understandings of upper-atmosphere patterns.”
While the American team claimed to be able to confidently predict the weather four or five days out, the British “weren’t prepared to do [that], out of their understanding” of the unpredictable nature of British weather patterns, says meteorologist Martin Young in the production notes for Pressure.
A former deputy chief for the Met Office, Young led a team of meteorologists who advised the filmmakers on how to accurately convey the nuances of weather forecasting in the U.K. “During the initial discussions,” he says, “Anthony was keen to paint a picture of how the information got to the weather forecasters from where the observations were taken: on remote stations, out over the sea, weather balloons, all that sort of thing.”
The Forecast for D-Day
When Stagg first joined the forecasting team, Eisenhower had yet to be selected as supreme commander of the Allied forces in Europe. (He was appointed in December 1943.) With this role still empty, the timing of the invasion remained up in the air, but planners told Stagg that May 1944 “was the most likely time; it could be later but almost certainly not earlier,” as he recalled in his memoir.
Operation Overlord was slated to be a massive undertaking involving land, sea and air forces, each of which had competing requests for ideal weather conditions on D-Day. Although the Nazis expected the Allies to land at Calais, a spot closer to the English coast, military commanders decided on Normandy instead in hopes of taking the enemy by surprise.
As Charlton-Perez tells Smithsonian, Stagg had to balance a host of weather requirements to narrow down the timing of the invasion. Branches raised concerns regarding cloud cover, tidal conditions, wind speed and visibility, “so the invading forces could see each other and see the defenses as they landed.” The meteorologist adds, “If you think about it as a forecasting problem, these multiple conditions have to be met at the time of the landing, and, of course, the technology that was available to make those predictions was vastly different to the technology we have today.”
According to Stagg, “If every one of the requirements that I had been given was to be insisted on, it was easy to deduce that Overlord might not get underway for another hundred years or more.”
When none of the units volunteered to adjust their demands, Stagg was forced to come up with his own list of weather conditions that had to be met for the invasion to succeed. Wind speed was one of the most critical factors: Anything over Beaufort Force 4, the standard still used today, could spell disaster. Ultimately, Eisenhower pinned down the timing of the operation to two potential three-day windows—June 5-7 and June 19-21—before selecting June 5 as the preferred date.
From the start, Stagg recalled, “strong personalities and mannerisms of the participants” sparked disagreements among the meteorologists, with Krick and Sverre Petterssen, head of the Dunstable team, clashing the most. “Each was confident in his own diagnosis and prognosis, [and] each had an aptitude for dogmatic assertions, relaxation from which became harder as the discussion progressed,” Stagg observed. As historian Antony Beevor writes in D-Day: The Battle for Normandy, each bureau “received the same reports from the weather stations, but their analysis of the data simply did not match up.”
Beginning in early June, Stagg presented two daily briefings to Eisenhower and the other Allied commanders, doing his best to mask the disagreements that plagued the three forecasting centers. On June 2, Dunstable outlined an “unmitigatedly pessimistic” view of the coming days’ weather, Stagg recalled, predicting winds up to Beaufort Force 5 and generally stormy weather; Widewing offered a more optimistic forecast of light winds and clear skies. Stagg found the Dunstable outlook to be more realistic.
On June 3, Stagg delivered his forecast to the commanders, predicting that a high-pressure system over the Atlantic Ocean would lead to winds of up to Beaufort Force 6 at times, dense cloud cover, limited visibility and fog. Eisenhower said, “Last night, you left us, or at least you left me, with a gleam of hope. Isn’t there just a chance that you might be a bit more optimistic again tomorrow?”
Stagg’s response was straightforward: “No, sir. … Tonight the balance has gone too far to the other side for it to swing back again overnight tonight.”
Early the next morning, Stagg touched base with the forecasting centers to go over the latest weather data. “If ever in the history of weather forecasting there was an occasion for unanimity of view and confidence in the outcome, this was it,” he wrote in his memoir. “Instead, here was a deep cleavage and uncertainty.”
Over the protests of Krick and the American contingent, Stagg told Eisenhower that the outlook hadn’t improved. “Weighing all factors,” Eisenhower later wrote, “I decided that the attack would have to be postponed,” likely to the second window in June if poor weather persisted over the following days. The general recalled the thousands of men already in the Irish Sea and the Channel in preparation for the invasion, hoping to avoid alerting the Germans of the timing of the attack.
Later on June 4, the forecasters finally caught a break. New data suggested that a cold front would produce an unexpected lull in the severe weather on June 6, with winds around Beaufort Force 4, although the bureaus disagreed on the conditions that would follow in the days after that. As Stagg tells Eisenhower in Pressure, the Nazis will “never see it coming, sir, a gap like this in the storm.” He adds, “The weather won’t be perfect. But it will do.”
In his memoir, Eisenhower wrote that the uncertain forecast for June 7 onward posed difficulties for the invasion “because of the possibility that we might land the first several waves successfully and then find later buildup impracticable.” Still, he added:
The consequences of the delay justified great risk, and I quickly announced the decision to go ahead with the attack on June 6. The time was then 4:15 a.m., June 5. No one present disagreed, and there was a definite brightening of faces as, without a further word, each went off to his respective post of duty to flash out to his command the messages that would set the whole host in motion.
The Legacy of the D-Day Forecast
On June 6, 1944, nearly 160,000 Allied troops landed on the beaches of Normandy, supported by 23,400 airborne troops, 1,200 warships and 12,000 aircraft. By the end of the month, more than 850,000 Allied troops had arrived in Normandy, paving the way for the liberation of Europe. The Allies retook Paris in August 1944 and fought their way into the heart of Berlin in May 1945, bringing the war in Europe to a close on May 8.
Back at headquarters on D-Day, Stagg and his colleagues concluded that their “forecast advice to the supreme Allied commander had been vindicated.” (More recently, Dan Suri, a meteorologist at the Met Office, told the New York Times that the conditions the forecasters had predicted came to pass but maintained that they were off base regarding the causes of this break in the weather.) The timing of the attack took the Germans by surprise, as their forecasters had assumed that poor weather in the English Channel would prevent the Allies from landing any earlier than June 10.
If the Allied meteorologists hadn’t predicted a lull in the weather on June 6, the invasion would have been postponed until June 19. On that day, a “sudden and protracted storm … caused great havoc on the later buildup phase of the invasion,” according to Stagg. As Eisenhower wrote in the margins of a June 21 letter, “I thank the gods of war we went when we did.”
After World War II, Stagg returned to the Met Office. He was knighted in 1954 and published his memoir in 1971, four years before his death at age 74. Krick, for his part, claimed credit for the invasion forecast until his death in 1996. As early as 1954, he wrote that if not for his team, “all the mighty preparations for D-Day might have gone for naught, and the war in Europe might have gone on for years.” Krick remained a controversial figure in the meteorological community; at one point, several of his Caltech colleagues prepared a report stating, “He claims to do things that he can’t do. He claims to have done things he didn’t do.”
In his memoir, Eisenhower wrote, “Some soldier once said, ‘The weather is always neutral.’ Nothing could be more untrue.” Stagg would probably have agreed with this assessment. As he asks Summersby in Pressure, “How can the weather be boring? It feeds us. The weather can destroy us. It controls our daily life. I don’t think that’s boring.”
Source: Smithsonian Magazine