Source: BBC News D Day and the weather crucial role | YouTube
Months and years of waiting were over.
In early June 1944 thousands of man and tons of equipment were massing on the shores of Southern England waiting for the moment to launch the D-day offensive, but there was one thing that was crucial to the success and timing of that operation - the weather.
Poor conditions would jeopardize the whole invasion preventing aircraft from flying and ships from landing troops on the Normandy beaches. There was enormous pressure on weather forecasters being asked by Eisenhower to predict up to five days ahead at a time when even a forecast of 24 hours was a challenge. The man at the sharp end at the whole forecast operation was Group Captain Stag.
The technical use weather just be able to pick up some little interlude which would be unknown to the enemy forces that would allow us to make use of it and catch the people on the other side unaware.
Meteorologist Stan Cornfo explained the huge difficulties that Stag had to overcome.
It was his judgment that was brought to bear among forecast which were often very very different because the subject wasn't anything like as advanced as it now is. There was a war on so you didn't get too much information, and yeah it was just his strength of character perception that got us through. Weather forecasting is pressured enough these days, but imagine seventy years ago when the decision to forecasters preparing aircraft like this one to head into D-day could actually decide the outcome of the second world war.
Even now we're still finding new information. These weather charts recently discovered by meteorologist Anders Person show that the Germans had much better knowledge of the weather over the Atlantic than previously thought.
The allied commander Eisenhower made the right decision from wrong information, but Rommel made the wrong decision with fairly correct weather information.
So it seems the Germans may have one the battle at the forecasts but if the invasion had been delayed until the next suitable tide two weeks later gales would have destroyed any chances of a landing and history would have been very different.
Peter Gibbs, BBC News