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Breakdown: Why weather played an important role on D-Day

Updated: Jun. 6, 2021 at 3:19 AM CDT
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MEMPHIS, Tenn. (WMC) - Seventy-seven years ago, Allied forces landed in northern France as part of a military action that paved the way for the defeat of Nazi Germany, molding the course of world history.

Perhaps the most important weather forecast ever made was the one for D-Day.

Originally, the invasion of France had been scheduled for June 5, 1944.

It was one of just three days that month when the moon would be bright enough for paratroopers and pilots to see and work effectively. Additionally, the tide had to be low enough for the landing parties to clear mines, barbed wire, and other defenses on the beaches.

Finally, relatively clear skies and calm seas were necessary in order to make this invasion a successful one.

At the time, weather forecasting was a young science; there were no satellites, no radar, and no computer models.

A team of six meteorologists – from the U.S. Army Air Corps, the British Royal Navy, and the British Meteorological Office – worked for months sharpening their forecasting techniques before advising Allied commanders, led by General Dwight D. Eisenhower, the best time for attack.

As D-Day neared, the American meteorologists, based on a forecasting method that gave great weight to historical weather conditions for a given date and location, predicted fair weather for June 5 and they pushed for the invasion.

However, the British forecasters took a different approach by analyzing measurements of temperature, pressure, and humidity to try to map out weather fronts.

Unlike the American meteorologists, the British teams predicted low clouds and stormy weather on June 5. Therefore, on the evening of June 4, Captain James Martin Stagg, the highest ranking of the meteorologists, convinced Eisenhower to postpone the invasion by 24-hours.

It was a decision that would prove crucial as the British forecast ended up panning out. The weather on June 5 did, in fact, bring rough seas and 25-30 mph winds in the English Channel.

Below is a look at the weather map for June 5, 1944. Notice a weather front right near Normandy. That meant clouds, strong winds, and heavy rain.

D-Day weather pattern June 4-5, 1944
D-Day weather pattern June 4-5, 1944(WMC)

Due to the inclement weather, German soldiers were allowed to leave their posts at the beaches. According to NASA, German forecasters had predicted that gale-force winds would arrive on June 5 and persist until mid-June. The Germans were so confident that the Allies would not dare attack that they allowed many soldiers to leave their posts on the beaches and take part in war games in Rennes, France.

The challenges were many, so the hope was to give the landing forces the best chance possible, and the perfect moment occurred at 1:18 a.m. on June 6.

Had the invasion not occurred at that moment, the next opportunity for a full moon would have been two-weeks later on June 19. Which, that day, a severe storm hit the Channel and destroyed one of the two Mulberry harbors and damaged the other.

Still, that single day of June 6 cost the lives of 4,414 Allied troops, 2,501 of them Americans. More than 5,000 were injured. On the German side, several thousand were killed or wounded.

The Battle of Normandy, code-named Operation Overlord, accelerated Germany’s defeat less than a year later in May 1945.

This instance isn’t the only time weather played a dramatic role in the outcomes of wars. For example, a major turning point in the American Revolution was Washington crossing a frozen Delaware River on Christmas evening.

You can read a full account of the impact of weather on D-Day from NASA.

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