Weather forecasting was based on hand-drawn maps and observations taken by men and women in the 1940s.
Assistant State Climatologist, Pete Boulay laughs, "It would have been a challenge being a meteorologist back then, that's for sure."
The Allies needed calm seas and low tides for boats and minimal cloud cover for planes and paratroopers. In a very stormy period, a small break in the weather made June 6th D-day based on the forecasting of British and American meteorologists.
"Some things haven't changed, in order to make a good forecast you need lots of data. Without that data its harder to forecast," he continues.
The Allies had data that the Germans did not.
"The Germans didn't have sites in the Atlantic Ocean and Greenland and Iceland where they could see fronts coming in," explains Doug Bekke, Curator of the Minnesota Military Museum.
Boulay adds, "So in a way its was lucky that the weather was so poor because it fooled the Germans into thinking there wasn't going to be an invasion that day."
"The German weather predictions were such that they thought it was going to be impossible for an Allied landing," continues Bekke.
The weather didn't end up being ideal, but it was good enough.
Bekke finishes, "It worked, Ultimately it worked."