The most important weather forecast in history - D-Day 1944

Canadian Troops landing on the Normandy Coast, June 6, 1944

Friday is the 70th Anniversary of one of the most important dates of the 20th Century, D- Day, June 6, 1944. The invasion of the Allied Forces at Normandy would be the start of the liberation of mainland Europe and the eventual end of World War II. On this day, I want to express my gratitude to all those brave men and women who paid and continue to pay the ultimate sacrifice so that we can enjoy our freedom. Without them, none of this is possible.

It would be one of the most important weather forecasts ever delivered throughout history. Nearly 160,000 Allied Troops, including 14,000 Canadians, would be relying on its accuracy. The entire free world had a interest in this forecast being correct. It was the forecast for the English Channel during D-Day, the Normandy invasion, in June 1944.

Supreme Commander of the NATO forces, General Dwight D. Eisenhower needed nearly ideal weather conditions to launch the invasion. The perfect day would have a full moon, low tides, clear skies, light winds and low seas. Two such periods matched the low tide scenario, but only one had the light of a full moon, June 5, 6 or 7, 1944.

Destroyed military equipment lies in the surf at Juneau Beach on D-Day, June 6, 1944

The prognostication fell on the backs of a team of forecasters from the UK and the USA, sprinkled with a few other Allied forecasters. The forecast team was lead by British meteorologist James Martin Stagg. Stagg lead three teams of forecasters who would argue back and forth for days testing each others abilities and theories to come up with the right day for the invasion of the Normandy Coast. The safety of the troops and the effectiveness of an entire campaign lay at stake.

It was up to the forecasters to give the best idea as to which 24-hour period would be best to launch the invasion. Early forecasts predicted stormy weather for the time frame in question. Eisenhower wanted a Beaufort Scale wind of 4 or less to give the go ahead. Force 4 winds are 13-18mph with 3.5 to 5 foot seas. Anything greater than that would swamp the landing craft and sink vital equipment. The challenges were many, so the hope was to give the landing forces the best chance possible. Any type of cloud cover would hinder air support and limit paratroopers.

American Troops landing at Omaha Beach, June 6, 1944

The massive Allied Force of nearly 200,000 troops, with over 6500 ships and hundreds of aircraft, began staging as early as June 3 in what had been up to that point a decent stretch of weather. That was about to change, as a series of low pressure systems and fronts travelling across the North Atlantic was about to bring very poor weather. By June 4th, the weather had turned with strong winds, low visibility, high surf and heavy rain. Stagg approached Eisenhower with his advice to delay the invasion and despite the US forecasters insisting the weather was acceptable for an assault, the General decided to wait 24 hours. Thousands of troops remained in place on ships in rough seas for an additional day. The armada was deployed instead in the early hours of June 5 for the 17-hour trip across the English Channel and a June 6 sunrise assault. Despite the 24 hour wait the weather was less than ideal with 5 foot seas, but a vast improvement over the 6 or 8 foot seas and poor visibility during the previous 24 hours. To show how devastating it could have been, even the lower wave action swamped several of the landing craft and left at least 2 dozen tanks submerged at Omaha Beach alone. This would lead to little ground support for Infantry, and massive casualties to the US forces.

The Germans were caught by surprise, as their forecasters had told German command the bad weather would last well into June and thus prevent any invasion. The rest as they say is history with the invasion succeeding but unfortunately at a terrible cost with as many as 10,000 casualties (dead & injured), including 1074 Canadians (359 Canadian deaths). Eleven months later Germany would surrender. You can never downplay the importance of D-Day in bringing World War II to an end. One can only imagine how much worse the invasion would have gone had Eisenhower decided to leave on the 4th while the cold front whipped up heavy rain and strong winds with very highs seas and low visibility. Stagg’s forecast to travel in the relative good weather between low pressure systems on June 5, 1944 no doubt lead to the success of the invasion, as well as saving countless lives.

By the time the initial battle came to an end, the sun was shinning along the Normandy coastline.