How accurate was the movie PRESSURE?

PRESSURE is based on a true story. The central themes, disagreements and scientific knowledge displayed on screen are a broadly accurate re-telling of one of the most important weather forecasts in history.

Group Captain Dr James Stagg was responsible for working with teams of meteorologists, both American and British, to deliver the forecast to the highest levels of military command on the potential impact of the weather on the D-Day plans.

The film’s producers, Working Title and STUDIOCANAL, took great care to bring the story to life and visited the Met Office during pre-production to collect resources and quiz subject-matter experts to help bring realism on to set.

Met Office Library and Archive Manager Catherine Ross said: “It was great to see the lengths the film crew went to in order to bring the historical reality of the D-Day forecast to the big screen.

“Scans of maps, reference books, output from teleprinters at the time. You name it, they wanted to see it. Such was the level of detail; they even sourced original printing presses from the time so each document would have the correct opacity and feel. While there’s inevitably some creative license to produce a film, what you’re seeing on screen is a great re-enactment of some of the tension, disagreements and people behind the most important forecast in the Met Office’s history.”

This blog will contain some minor spoilers for the movie and some of its plot points, though the outcome of D-Day isn’t technically a spoiler.  

Exercise Tiger

One of the earliest moments shown in the film is the depiction of the disaster of Exercise Tiger – one of the most important rehearsals for the D-Day landings. Communication problems and a lack of co-ordination led to substantial challenges during the exercise at Slapton Sands, Devon, with a number of friendly-fire casualties as well as an attack from a German E-boat during the exercise.

While the film doesn’t specifically mention the German attack during the exercise, the event did indeed loom large in the thinking of the commanders tasked with planning D-Day.

Who's who?

One of the central themes in the film is the disagreement between Stagg (Andrew Scott) and Lieutenant Colonel Irving P. Krick (Chris Messina), who was an American meteorologist.

Stagg joined the Met Office in 1924 and was a skilled meteorologist and expert in terrestrial magnetism. He was also no stranger to challenging environments, having led the British Polar Expedition of Arctic Canada in the winter of 1932/33. Appointed as Chief Meteorologist at the Supreme Headquarters Allied Expeditionary Force (SHAEF) - the Allied headquarters planning D-Day - Stagg was responsible for coordinating meetings between the three lead forecasting teams from the Met Office, US Airforce, and the Royal Navy. He was then responsible for presenting a single operational assessment to Allied commanders.

Interestingly, the often-gloomy depiction of Stagg in parts of the film is backed up by historical observations. Admiral Sir George Creasy, from the Royal Navy, famously remarked on Stagg: “Here comes six feet three inches of Stagg and six feet two inches of gloom.” The remark reflects the atmosphere in the run-up to D-Day with Stagg repeatedly bringing unwelcome news to Eisenhower and senior commanders.

Stagg, based at Southwick House during the invasion period, was directly responsible for the weather briefing for General Dwight D. Eisenhower (Brendan Fraser), who had ultimate responsibility for the decision-making on timings.

Not depicted in the film was Colonel Donald Yates, who was an American weather officer and was effectively Deputy to Stagg at SHAEF. Stagg and Yates worked together to consider assessments and present advice to the commanders.

While Stagg and Yates were based at Southwick House in the build-up to D-Day, American forecaster Krick was actually based at Bushy Park, working with fellow forecaster Ben Holtzman using their analogue forecasting method. They were in frequent direct communication with Stagg about their forecast and the forecasting disagreements between the different teams are well documented.

Other forecasters working on the D-Day forecast from the British side not depicted in the film were Charles K. M. Douglas, Senior forecaster at the Met Office headquarters in Dunstable, and Sverre Petterssen, a Norwegian meteorologist also based at Dunstable and worked closely with Douglas and the Met Office during the war. Petterssen was a pioneer on work around understanding upper air observations during the war. The Royal Navy also had forecasting teams looking specifically at sea conditions and joined the daily telephone conferences with Stagg.

Meteorological methods

At the time, forecasting methods varied and had different levels of success in different scenarios.

It’s true that the American and British meteorological teams disagreed on the suitability for D-Day to occur on 5 June. Krick’s American team favoured analogue forecasting, which compared historical patterns to current conditions and favoured a go-ahead for 5 June. However, the British approach, which looked at synoptic evolutions of fronts and upper-air conditions, indicated more dangerous weather on 5 June.

The central disagreement is accurate, but Stagg’s role was a little more nuanced, effectively working as a coordinator between the teams, including naval forecasts from the Royal Navy, to determine the precise forecast. The forecast itself was a collaborative process between all the teams, with Stagg and Yates ultimately reporting directly into SHAEF and Eisenhower.

The understanding of the jet stream – which is still communicated in Met Office forecasts today – was in its relative infancy at the time, but the British forecasters were fully aware of the importance of upper-air observations and the interaction between that and conditions at the surface, as shown in the film.

The maps and charts displayed on screen throughout the film are accurate, with a pre-production crew visiting the Met Office’s Library and Archive to capture as much of the historical reality as possible.

Working on the D-Day forecast

One of the primary differences to the historical accuracy is fairly early on in the film. PRESSURE implies that Stagg was hauled in to work on the D-Day forecast with just 72 hours until the planned invasion of the Normandy coast.

The reality is that Stagg had been working in wartime meteorological support since the start of the Second World War in 1939 and became Chief Meteorologist to SHAEF and ‘Operation Overlord’ – which was the D-Day plan – in November 1943, seven months before the invasion.

What is accurate in the film is that the forecast for D-Day itself would only have taken shape at relatively-short notice ahead of the planned date, so the stakes and pressure to be accurate for the day against demanding deadlines depicted in the film were indeed true.

The highly unseasonable and stormy conditions in early June 1944 that form such a key aspect of the film are also true. Such conditions had rarely, if ever, been seen in the British Isles in June making an accurate forecast even more challenging for Stagg and the D-Day meteorologists.

Forecasting in the 1940s was considerably more challenging than it is today – particularly beyond a day or two - and the latest observations, from sites and ships around the UK, Ireland and Europe, were crucial for meteorologists to work out the forecast. The film depicts the process of collecting observations and plotting them onto maps accurately. It’s these maps that ultimately helped determine and communicate the forecast.

Once the ‘weather window’ was identified to proceed with the invasion on 6 June, Stagg remarks in the film, “they’ll never see it coming,” which could refer to the fact that the Allies had more dense observations across Europe because the Enigma Code had been broken. In contrast, the German charts from the time were largely blank when it came to UK-based observations.

The image shows a weather chart for 5 June, 1944.

This difference in observing coverage contributed to German forecasters assessing the weather as unsuitable for an invasion. While the German forecast broadly anticipated continued poor weather, Allied forecasters identified a short interval of more favourable conditions on 6 June.

Maureen Sweeney and Blacksod Point

There's a reference to a crucial observation from Blacksod Point in County Mayo, Ireland. Maureen Flavin (later Sweeney) was an Irish postmistress and volunteer weather observer and some of her observations would prove critical in the forecasting for D-Day.

The observations at Blacksod Point were of such importance on 3 June that officials called directly to confirm them. While Sweeney herself wasn’t a forecaster or would have had any knowledge of the D-Day plans, her observations from the site were a crucial part of the puzzle for meteorologists.

The Met Office's most important forecast

PRESSURE is an accurate re-telling of the stakes, issues and disagreements had between expert meteorologists in the run-up to D-Day. The film takes some decisions to place characters in the same room who in reality were often located at different forecasting centres and communicating through secure telephone links, teleprinters and formal forecast discussions.

The film depicts real debates at the time and the genuinely unsettled and unseasonable weather of early June 1944. It also highlights the crucial role of Met Office defence forecasting during one of the most important days in history.

In addition to the work determining the timings of D-Day, meteorologists were also embedded in almost every aspect of Operation Overlord and providing the weather intelligence to make the invasion possible. Observers were also a crucial part of the ongoing operations, with weather-related experts working on every front in the war.

This involvement with defence still rings true for the Met Office today, with defence meteorologists stationed across the UK and overseas, and the Met Office’s deployable Mobile Met Unit (MMU), an RAF Reserve Unit, continues to support operations and exercises in the UK and around the world.

Find out more about the Met Office Library and Archive, including the Digital Library and Archive.