Meteorologist James Stagg gave what many regard as the most important weather forecast in history in June 1944. The fate of more than 150,000 Allied troops preparing to invade the Normandy beaches on D-Day and the future of the war in Europe depended on Stagg and his forecasting teams. Get the forecast wrong and an already perilous invasion might not succeed, prolonging the war. In the briefing room at Southwick House near Portsmouth, waiting for the forecast, sat General Dwight D. Eisenhower.