75 years since the most important weather forecast in history

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Allied forces weather map from the morning of June 6, 1944 showing a storm northeast of what is now the United Kingdom, and surface observations from the north Atlantic all the way to Russia... image courtesy of the UK Met Office

There have been many important weather forecasts over the last century and a half, but none likely more important than that of the D-Day invasion of June 6, 1944. One hundred thousand soldiers, 12,000 aircraft, 5,000 warships, and literally the fate of the world was in the hands of a few meteorologists.

Late May and early June 1944 proved to be a very stormy period for the western part of Europe with several storm systems rolling across the continent from the Atlantic. These storms could throw high winds, rough seas and low cloud cover at the invasion that could cripple any attack they would have on the Germans. So, the meteorologists were tasked with picking the day the invasion would occur based off of expected weather conditions.

While original plans were to invade on the 5th of June, that was scrubbed and delayed to the 6th, when three groups of meteorologists, led by James Martin Stagg, agreed there would be a brief lull in the storms long enough for their forces to make landfall. The Germans, however, were taken a little by surprise because their meteorologists did NOT predict this lull. It was this forecasting discrepancy that likely changed the course of human history.

The two images above are zoomed in handwritten archived drawings courtesy of the UK Met Office from the Allied meteorologists as well as the German meteorologists.

The Allied map on the morning of June 6, 1944 shows current observations from areas into the north Atlantic (likely from ships or aircraft) through the U.K., France and all the way to Russia. However, the German map only shows observations from German occupied territories or in locations they had spies.

Notice the lack of data from the U.K., Ireland, and the north Atlantic. It was likely this lack of data that ultimately led to the Germans inaccurate forecast, because in this part of the Northern Hemisphere, just like North America, our weather generally comes from the west.

Well, with no observations from the west, and no modern day satellites to be able to see that far away, the Germans were unaware of where any storms were located or where they would track. You can’t exactly forecast what you can’t see.

So how did the Allied forces have so many surface observations across Europe when they were controlled by the Germans?

The Allies captured and decoded their enigma machines giving them access to secret German information, which included weather reports. So, pretty much every mission leading up to that day helped the Allies beat the Germans. From then on, the United States, the U. K. and many other nations around the world considered weather forecasting as a national security matter and have invested tens of billions of dollars to get to where we are today.