Image: AP Photo/Associated Press
The forecast for northwest France on June 6, 1944 stands as history's most important weather forecast. Conditions at Omaha Beach and the other landing zones within about 50 miles of Normandy, France had to be just right so as to allow troops to parachute to their landing zones, as well as maneuver their way onshore via amphibious vehicles.
With so many military assets being deployed â€" more than 5,000 ships, 13,000 aircraft and 160,000 Allied troops â€" the weather forecast, at a time when modern meteorology was still in its infancy, was crucial to the success of the mission.
Fog, strong winds or high waves could have proved disastrous.
Allied Forces' D-Day weather map showing weather observations in western Europe.
Credit for the accurate forecast belongs to a Scottish geophysicist named James Martin Stagg, a group captain in the Royal Air Force and chief meteorological officer at Supreme Headquarters Allied Expeditionary Force. According to the U.K. Met Office, where he worked, as well as a new book called The Forecast for D-Day, Stagg helped convince allied leaders to postpone the invasion by one day due to inclement weather conditions.
Other weather forecasters at Supreme Headquarters disagreed, thinking the weather on June 5, the original date for the invasion, was good enough.
The UK Met Office says the invasion took place during a generally stormy period, with June 6 constituting a brief window of opportunity, albeit not a crystal clear, calm day. On its website, the agency says:
What troubled the meteorologists in the days leading up to D-Day was a parade of storms that barreled across the Atlantic and into the British Isles, any one of which would have stirred up the dangerous waters of the English Channel where the fleet was gathering, and provided unwelcome cloud cover for the aerial assault of Normandy.
To make an accurate forecast, the allied forces relied on observations from weather reconnaissance missions off the east coast of Greenland and Norway, and also used German observations (by then the Allies had cracked the Germans' encryption code, known as Enigma.)
German weather chart for D-Day, on June 6, 1944.
Weather forecasting was in a relatively primitive state in 1944 compared to the modern satellite and supercomputer-heavy approach of today. Forecasts were prepared using data from ships and land-based stations, as well as aircraft. Charts were hand-drawn every few hours, according to the Met Office.
The weather was considered a matter of national security. For this reason neither side issued public weather forecasts for the duration of the war. However, because the Allies had cracked the German Enigma code, the D-Day forecasters had access to German meteorological observations as well as observations from Allied observers and reconnaissance flights. This is shown on the weather charts held in the Met Office National Meteorological Archive in Exeter.
It wasn't until after the war that the Allies discovered they had a superior weather operation compared to the Axis. The German military's weather chart for D-day showed a lack of weather observations from the U.K. and Europe, as well as parts of the Atlantic.
German forecasters, operating with fewer observations than the Allied forces, missed the June 6 weather window entirely â€" instead predicting that conditions would remain too stormy for an Allied assault.
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