Eighty years ago today, on June 6, 1944, almost 160,000 Allied soldiers stormed onto the shores of Normandy, France. Now known as D-Day, Operation Overlord helped to change the course of World War II and was unprecedented in scale and audacity. The invasion took careful planning, secrecy and very particular weather conditions. The forecast played a pivotal and historic role in the execution and overall success of D-day.
The Allied forces needed a full moon and a low tide for optimal ship landing and navigation ashore. Easy to find the dates, but that was still only a few days in both May and June. Eventually, it was decided that D-day would be scheduled for June 5. While they had the date, the weather also needed to cooperate. Perfect conditions called for clear skies, calm seas and calm winds.
And the forecast for June 4-7 1944, proved to be a tricky one. It is important to remember the meteorological team was operating without the technology of today. Weather predictions of more than 24 to 48 hours in advance were unrealistic. In fact, most forecasts were made based on military and even civilian weather observers. Chief Meteorologist British Capt. James Stagg used the observations by a post office worker in Northwest Ireland, Maureen Sweeney to make his forecast. She first observed the storm that would make for rough seas and high winds on June 5, but she also reported a brief rise in barometric pressure, signaling a small window of calmer weather and an opportunity for the Allied Forces to invade.
The call to postpone the invasion was made on June 4. The other dates up for consideration were June 6 and June 7. Neither day was going to have perfect weather, but if the Allied forces waited any longer, they would have to wait another two weeks.
Using Sweeney's observations and Stagg's forecast, General Dwight D. Eisenhower decided to make the switch to June 6. The weather was still not ideal and caused major problems for Allied troops. Strong winds and rough seas caused paratroopers to land miles off their targets, and some boats were even capsized. However, German forecasters did not have the surface observations the Allied forces had. They believed that the stormy forecast would last for days, if not weeks and ultimately delay any invasion, taking the Nazis by surprise. This may have just been the most important forecast in world history and marked the beginning of the end of Nazi occupation in Europe.
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