The weather forecast that shaped the course of D-Day

One of the most crucial forecasts ever made

Meteorologists have predicted the weather for some of mankind’s biggest and most significant historical events. Probably the most notable is the weather forecast for D-Day.

In June of 1944 German forces were expanding their reach across Europe. The need for an invasion of some kind was recognized by British Prime Minister Winston Churchill to help liberate France.

It was realized far in advance by Allied command that an accurate weather forecast would not only be ideal, but mandatory for the mission to be completed. In a time of no doppler radar, satellite imagery, or computer models, six allied teams of meteorologists led by American Chief Irving Kirk studied nearly 50 years of old June weather maps and history. They also used what limited observation stations they had access to at the time to make the most crucial forecast in American history.

The team of meteorologists had identified June 5th through the 7th as a possible window of opportunity to carry out the invasion. This is because they were planning around the tide cycle and moon phases, trying to hit the highest tide and brightest moon at the same time. That also meant the Allies only had 3 days a month where these conditions would be met. If the weather didn’t cooperate on any of these three days, that could have spelled big trouble.

On the morning of June 4, Allied meteorologists advised General Dwight D. Eisenhower that storms would plague the area the next day. Aircraft would struggle and naval guns would be tough to handle in the high winds and rain. Upon receiving that information, Eisenhower ordered the invasion moved to June 6, when the team thought a break between weather systems would arrive. Calm seas were desired for the Navy, while high tides were requested by the Army to shorten the amount of exposed beach as soldiers landed. After being briefed by Stagg, Eisenhower made the decision to invade June 6.

With some luck and a lot of hard work, the forecast verified almost perfectly, and the invasion was successful. The Germans were not ready, because the weather had been so bad on the 5th. German meteorologists failed to pick up on the weather patterns, because they severely lacked in knowledge and weather station data. The Germans had no clue the break in the weather was coming, but the Allies did, thanks to who Eisenhower called “the best group of meteorologists out there at the time.”