[D-Day] Complete Broadcast Ep. 5 (06 Jun 1944)

Weather

The invasion planners determined a set of conditions regarding the phase of the moon, the tides, and the time of day that meant only a few days in each month were deemed suitable. A full moon was desirable, as it would provide illumination for aircraft pilots and have the highest tides. The Allies wanted to schedule the landings for shortly before dawn, midway between low and high tide, with the tide coming in. This would improve the visibility of obstacles on the beach, while minimising the amount of time the men had to spend exposed in the open.^[37] Eisenhower had tentatively selected 5 June as the date for the assault. However, on 4 June, conditions were clearly unsuitable for a landing; high winds and heavy seas made it impossible to launch landing craft, and low clouds would prevent aircraft from finding their targets.^[38]

Group Captain James Stagg of the Royal Air Force (RAF) met with Eisenhower on the evening of 4 June. He and his meteorological team predicted that the weather would improve sufficiently so that the invasion could go ahead on 6 June. After much discussion with the other senior commanders, Eisenhower decided that the invasion should go ahead on the 6th. Had Eisenhower postponed the invasion, the next available date with the correct combination of tides (but without the desirable full moon) was two weeks later, from 18 to 20 June. But, during this period, they would have encountered a major storm that lasted four days, between 19 and 22 June, which would have made the initial landings impossible to undertake. (Wikipedia)