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How did weather forecasting influence the timing of the Normandy invasion in 1944?

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Weather forecasting Doppler radars, such as this one operated by the U.S. National Weather Service at New Underwood, South Dakota, extract the Doppler frequency shift of the echo produced by a moving target by noting how much the frequency of the received signal differs from the frequency of the signal that was transmitted.

Weather forecasting played a decisive role in the timing of the Normandy Invasion in 1944. While the operation was originally scheduled for early June, the invasion was heavily dependent on specific meteorological conditions to ensure the safety of the amphibious assault and the effectiveness of Allied air cover.1

In the days leading up to the planned June 5 launch, the English Channel experienced severe weather, including high winds, stormy seas, and low-lying rain clouds. These conditions threatened to disrupt the landing craft and ground Allied aircraft. Consequently, General Dwight D. Eisenhower made the difficult decision to postpone the invasion by 24 hours, even requiring the recall of ships that had already departed for the crossing.12

The final decision to proceed rested on the advice of chief meteorologist James Martin Stagg. On the night of June 4, Stagg informed Eisenhower of a potential temporary break in the weather. Relying on this forecast, Eisenhower authorized the invasion for June 6, a window that allowed the operation to proceed without serious weather-related disruption.12