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Alex Bailey/Focus Features

This story contains spoilers for the film Pressure.

Meteorologists are rarely the heroes of major Hollywood movies. Never say never.

The new film Pressure is a lightly fictionalized version of the actual lead-up to the D-Day invasion of France by Allied troops during World War II, and the crucial role of meteorologists in deciding when that battle would happen. And it stars some big names.

Andrew Scott, most recently of Ripley fame, plays James Stagg, a Scottish meteorologist who is tasked with pulling together a D-Day weather forecast for Gen. Dwight D. Eisenhower, played by Oscar-winner Brendan Fraser.

Stagg is stressed out, to say the least. The movie's title alludes both to barometric pressure, and to the enormous responsibility that the D-Day planners felt, given that so many soldiers were sure to die in the assault on Normandy's beaches. The Allied commanders also knew that, if the invasion failed, the Germans would have the upper hand.

There was a lot of pressure on meteorologists to get the forecast right, says James Taylor, the principal curator at the Imperial War Museums in the United Kingdom. "They had an absolutely key role to play in the planning of D-Day."

But the main drama in the film comes not from the interpersonal conflict between stressed-out weathermen in well-tailored uniforms, but from the science of weather forecasting itself. The movie depicts how a now-obsolete method of weather forecasting that was popular in the United States leading up to World War II was replaced by more modern methods that were taking root in Europe at the time.

"It's really a seminal moment for the entire meteorological community," says Louis Uccellini, who led the National Weather Service from 2014 to 2022. "And that was brought forward for societal benefit post-World War II."

Here are three things that Pressure gets right about modern weather forecasts, according to scientists and historians.

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WWII Weather Tip #1: The future doesn't necessarily look like the past

Until World War II, weather forecasting in the U.S. mostly relied on a simple principle: past weather patterns are similar to future ones. Basically, look to the past to predict the future.

In the movie Pressure, that school of thinking is embodied by the meteorologist Irving Krick, who led the American forecasting effort for the Allies. In the days leading up to D-Day, "Krick was doing trend analysis," explains Frank Blazich, a military historian at the Smithsonian's National Museum of American History in Washington, D.C.

The D-Day invasion was originally planned for early in the morning on June 5th, 1944. "Eisenhower needed a really strong weather forecast," Blazich says. "You need clear weather and a full moon to bring in aircraft at night," as well as clear skies and no low clouds, so ships could see targets on shore clearly.

Krick was looking back at weather patterns that had occurred on that date in the past, to predict what would happen in 1944. And, based on the past weather, he was certain there would not be a storm. "Mark my words, D-Day will be calm and sunny," Krick says in the film.

But other meteorologists disagreed. There were two other groups feeding weather information to Eisenhower, both of them staffed by European scientists. Their forecasts were based not on past patterns, but on real-time measurements of what was happening in the atmosphere from Newfoundland to Ireland. Those measurements clearly showed a storm headed for England and France.

In the end, the Europeans were correct, and D-Day was postponed to June 6.

After World War II, that new weather forecasting method took hold in the U.S., says Uccellini, and allowed for much earlier and more accura