Story by Paul Shirk on 06/10/2019Seventy-five years ago, Allied forces began the task of opening the second front in Europe when they landed on the beaches of Normandy, France on June 6, 1944.
Weather was a key factor in deciding when and where the invasion would take place. There were competing priorities when selecting the desired conditions for the invasion.
"You have to think of all the many varied platforms that would be used to launch the offensive, each one needed certain conditions," said Kent Sieg, 557th Weather Wing historian. "Bombers needed clear sight to targets. Tides had to be low to expose obstacles, but could not be too low or troops would have too long a distance to get to shore."
Selecting a date that would be the best compromise for these requirements was the challenge. The time determined to be most favorable for an offensive was a full moon. Had Stagg and his team delayed the invasion until the next full moon, June 19, Allied forces would have faced one of the largest storms in the English Channel in almost 80 years and D-Day may have very well failed.
Two meteorologists were appointed to the invasion planning staff, one English and one American, Group Captain James Martin Stagg, who was commissioned in the Royal Air Force Volunteer Reserve after serving with the British Meteorological Office, was appointed to the senior position and the American representative was Col. Donald Yates, who joined General Eisenhower's planning staff in the deputy position after serving as the Army Air Force Deputy Director of Weather.
"The first week of June 1944 would be a good time," said Sieg. "This is based upon the lunar cycle and its impact on tides, as well as atmospheric factors including wind, precipitation and cloud thickness."
On June 3, the team decided that weather did not look favorable for June 5. Early the next day, there was enough information indicating that June 6 would have operationally-acceptable weather.
"There was rough weather coming in on June 5," Sieg said. "They had seen behind it a clearing, a brief area of high pressure between Iceland and Ireland, moving east, that would come through behind a significant active weather system."
German forecasts believed weather for most of early and mid-June was too poor to support an invasion and had relaxed their alert level. Field Marshall Rommel took leave from the coastal defenses to celebrate his wife's birthday.
"Of course the enemy might have known about the incoming front as well, but had lost much of its weather reconnaissance capability to Allied air superiority and had stood down," Sieg said. "The enemy's lack of preparedness became a key element of the D-Day story."
The decision to wait was the right one. A situation report June 6, from Eisenhower to Gen. George Marshall stated, "The weather yesterday which was original date selected was impossible all along the target coast. Today conditions are vastly improved both by sea and air, and we have the prospect of at least reasonably favorable weather for the next several days."