Friday marked the 70th anniversary of the Allied invasion of Europe and the beginning of the end of Nazi tyranny and murder in World War II. A perfect combination of full moon (for nighttime aerial navigation purposes), low tide (so that German mines in Brittany would be exposed) and light winds were necessary to give the invasion any reasonable chance of success.
Thus, days on which the tides and phase of the moon were optimal were known some weeks in advance. As late May arrived, it became increasingly clear that choosing among those optimal days for invasion would depend crucially upon the weather and the ability to make an accurate forecast of weather conditions.
In 1944 there were no satellites and no weather radar. In addition, there was no such thing as numerical weather prediction by high-speed computers. Thus, a one-day forecast for western Europe, with the Atlantic Ocean stretching endlessly to the west, was informed only by careful analysis of surface observations and a few upper atmospheric observations near Iceland and Greenland.
The Allies had a rather unorganized approach to the forecasting enterprise, employing a British and an American team of forecasters. These two teams used decidedly different techniques to make their forecasts, and the differences came to a head on June 4 when, in the face of very different forecasts, Group Capt. James Martin Stagg, Gen. Dwight D. Eisenhower’s chief meteorologist, advised the general to delay the invasion one day, from June 5 to June 6.
The British forecast team bet that there would be a sufficiently calm period between two of the endless collection of storms that battered western Europe in June 1944 to allow the invasion to proceed on June 6. They turned out to be right.
While riding to the Capitol on his inauguration day in 1961, President John F. Kennedy asked President Eisenhower why the Normandy invasion had been so successful. Eisenhower answered, “Because we had better meteorologists than the Germans.”