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Historical meteorological documents show weather conditions ahead of D-Day invasion
9 September 2026
Historical documents detailing how weather conditions helped select the day of the Allied invasion of France in June 1944 have been discovered.
The original Second World War-era bound volumes of the Naval Meteorological Branch Periodical Letters (1939-1946) show the daily weather evaluations in the lead up to D-Day on June 6 and how they influenced the date of the invasion.
Written on June 22, 1944 the primary discovery among the documents is a since declassified report written by Group Captain James Stagg showing meteorological implications for the invasion, including strict weather limits for naval forces, air forces and ground forces.
It has statistical calculations proving the extreme rarity of acceptable weather conditions in June (ranging from 13-to-1 to 24-to-1 against) and details on the daily forecasting conferences held at 0630, 1730 and 2100.
Also reported are weather conditions experienced by assaulting forces and lessons and recommendations for military command, many of which still apply today.
The timely discovery at HMNB Devonport, in Plymouth, comes ahead of the release of movie Pressure which tells the story of UK Met Office Meteorologist Group Captain Stagg and General Dwight D. Eisenhower in the 72 hours before D-Day as they decide whether to launch the invasion.
The historical documents also detail the creation of the Admiralty Met Section in 1939 – a 24-hour operations division with instructor commanders, lieutenants and staff.
They show how the Royal Navy and meteorologists used complex statistical probabilities, early radar and scrambler telephone calls to advice Supreme Command on critical weather forecasts ahead of the crucial 1944 date.
The documents cover the meteorological section at Supreme Headquarters Allied Expeditionary Force, in Portsmouth, led by Group Captain Stagg (played by Andrew Scott in Pressure) and its daily coordination with the Naval Meteorological Forecasting Centre, Air Ministry Forecasting Central and the US Forecasting Central teams.
Key historic personnel named include Supreme Commander General Eisenhower as well as Instructor Commanders CT Suthons, TA Holden, J Fleming; Instructor Lieutenant Commander P Bracelin; scientific advisor HL Wright; and Instructor Commander WA Bishop.
Other reports included in the original official files and later lever-arch binders are Naval Meteorological Branch Periodical Letters (1939-1946) and Naval Weather Service Newsletters (1960-1970); internal Admiralty documents describing the creation of a 24-hour met section in the Operations Division; light-hearted historical material such as a 1943 Punch magazine extract titled The Met Man; and a declassified file detailing meteorological war plans in the Mediterranean dated 1935.
Lt Cdr David Gayle OiC Hydrographic, Meteorological and Oceanographic Training Unit (HMTU): "These documents provide a remarkable insight into the role meteorology played in the success of the D-Day landings.
“They demonstrate how critical environmental intelligence was to military decision making during WW2; an enduring truth that remains relevant to all military operations today.
“What makes this discovery particularly special is that it connects the meteorological specialists of D-Day with the METOC specialists we continue to train at HMTU, preserving an important legacy of operational excellence, scientific expertise and service to UK defence."