A little over 57 years ago, the second World War was in full swing, but the main protagonists could foresee the beginning of the end.
At Tehran, Churchill, Roosevelt and Stalin agreed that the Soviet summer offensive in the east would begin in June 1944. And in the West, Gen Dwight D. Eisenhower was more specific. He set June 5th as the date for an assault on Normandy "subject to last-minute revision in the event of unfavourable weather".
For surface operations in the English Channel, light winds, good visibility and relatively calm seas were a necessity. If the thousands of aircraft involved were to operate effectively, low cloud in any appreciable quantity could not be tolerated, and it was also desirable that the initial landings take place with the assistance of moonlight - to assist in identifying beach mines - and a rising tide.
It was calculated at the time that climatologically, the odds against experiencing these ideal weather conditions in early June were about 13 to 1, add on the moon and tide requirements, and the odds against were nearly trebled. As it happened, May 1944 was a very quiet month, but the weather of early June was unusually disturbed. Moreover, weather forecasting was difficult in those days, since the information available on which to base predictions was very sparse, and treated by both sides, within their own domains, as a closely guarded secret.
As Gen Eisenhower's designated D-Day of June 5th approached, it became obvious that a deep depression lay between Iceland and Scotland, and that its cold front was likely to be over the battle area at the crucial time, bringing rain, strong winds and low cloud to interfere with operations. On the advice of the meteorologists, operation "Overlord" was postponed to June 6th - 57 years ago today.
The depression to the north turned out to be one of the deepest ever to have affected these parts in June, with a central pressure of less than 980 hectopascals. And sure enough, it brought rain and winds of force 7 to the English Channel around the time for which the invasion had been originally planned. Had the landings gone ahead, the weather would have caused severe disruption, and might well have changed the course of history.
But all was well. By the morning of the new D-Day, the depression had lost much of its intensity. The channel was under the more benign influence of a light north-westerly breeze, and the weather was bright and clear. One of the most important forecasts ever issued had turned out to be correct - proving James Thurber's point that "He who hesitates is sometimes saved."