The Weather Forecast That Changed the Outcome of D-Day

The nation and the world commemorated the 82nd anniversary of D-Day on Saturday, June 6. While much has been said about the military strategy leading up to the battle that changed the course of history, what most people do not know is how the weather forecast was so important. Here is a look at the details of what ended up being one of the most significant weather forecasts in world history.

Six Meteorologists Held the Fate of D-Day in Their Hands

Meteorologists for the Allied troops spent the days leading up to the D-Day invasion of Normandy intently studying the weather forecast. It was up to the group of six Allied meteorologists to weigh in on the final go-ahead for the long-awaited invasion that would end up changing the course of the war, and humanity along with it.

Thousands of soldiers were depending on the Allied meteorologists to determine when the weather would be the most suitable for an invasion. Allied leaders had previously determined that they wanted to come ashore at low tide on the landing beaches. The military officials had also warned that the airborne units needed a full moon in order to have sustainable light for the drop.

In addition to the timing of the tides and the full moon, the Allied meteorologists were also looking at the forecast for sea conditions and winds. Rough seas and high winds could negatively impact the amphibious assault. Similarly, low clouds could be a hindrance to the necessary air support. Ireland's National Meteorological Service, Met Éireann, confirmed that the weather factors that would have the greatest impact on the success of the invasion were wind, cloud cover, and visibility.

James R. Fleming, president of the International Commission on History of Meteorology, detailed that six meteorologists were serving across three different teams on the Allied side. These teams were responsible for the D-Day forecasts.

The team of forecasters had decided by June 3 that June 5 would not be the best day for the invasion due to the weather. Most notably, a high-pressure system hovering over France would clash with an area of low pressure anchored to the northwest of Ireland. The clash of these two competing systems was forecast to produce strong southwesterly winds across the English Channel, making the seas too turbulent for landings. Met Éireann also noted that the cloud coverage would be too thick to conduct the planned bombing operations.

Just hours before the launch of the D-Day operations on June 4, British Group Captain James Stagg asked General Eisenhower to delay the invasion. Because the leaders wanted a full moon and a low tide at dawn, there were only a few possible dates to choose from for the attack. June 5 happened to be the first date in the slim three-day window.

The American meteorological team leaned on an analogue method that looked at both the current weather and historical conditions. Their forecast would most likely have ended in disaster for the Allied troops had they gone forward with the June 5 date, as a storm roared across the coast of France. Fortunately, Eisenhower followed Stagg's urging to postpone the invasion.