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The Toughest Weather Forecast Ever

It was probably the most momentous decision any sole individual made in the Second World War.

D-Day was originally planned for 5 June. Commitment had to be made two days before. Battleships in Scapa Flow had to sail south. Troops and tanks and other equipment had to be brought from inland bases to the ports and embarked. Airborne missions had to be set up, etc.

Eisenhower and his top commanders including his deputy, Tedder, Montgomery and Bradley had a small group of metrologists. At 2130 on 2 June the leader of the group was due to make his report. With the sun shining outside and the sky clear (double summer time), he spoke to his scattered team over the phone. There were of course very few weather reports from the Atlantic. That day there were indications of worsening weather in the Atlantic but no consensus among the group about what they meant. He hurried to the meeting. He followed his own instinct – “The whole situation from the British Isles to Newfoundland has been transformed in recent days and now is full of menace”. Several officers looked out of the window at the beautiful sunset bewildered. Eisenhower probed about 6 and 7 June and was told “I would be guessing, not behaving as your metrological advisor.” He left the meeting. In the room they decided there would be no change of the 5 June plan at least for the next 24 hours.

Early the next morning, 3 June, a weather station in western Ireland reported a rapid drop in pressure. At 2130 the team leader met Eisenhower et al again.”The fears we had yesterday for the next 3 or 4 days have been confirmed.” He described a gloomy picture of rough seas, Force 6 and low cloud (so debilitating passages for the landing craft soldiers, no air cover for the ships and the beaches, and a severe threat to the airborne landings.) Despite fine weather outside, Eisenhower felt compelled to order a postponement. It was calm all night.

At 0415 on 4 June there was another conference with Eisenhower. He decided the postponement must stand. Convoys were called back. Destroyers raced out to round up landing craft that had not acknowledged the radio signal. On 5 June it would be a full moon with spring tides, and at dawn it would be mid-tide, best disclosing obstacles and rising during the day. If the attack didn’t happen within a very few days the next window would be two weeks later, with a vastly increased risk the secret would get out and the Nazis could prepare.

By the evening of 4 June, the group noticed an approaching depression in the Atlantic had concentrated but slowed down. At the 2130 conference with rain and wind battering the windows, few felt optimistic. Eisenhower’s metrological advisor said that “since I presented the forecast last evening some rapid and unexpected developments have occurred over the North Atlantic”. There would be a brief improvement from afternoon of 5 June. Weather not ideal but it would do.

5 June Synoptic Chart

And so D-Day was on 6 June.

The leader was Dr James Stagg, who had been superintendent of Kew Observatory. He was given the rank of Group Captain to lend him the necessary authority in a military milieu. He made the most momentous decision made by an individual.

The value of using good weather forecasts!

Ted Sankey, Commodore

I am pleased to acknowledge Sir Anthony Beevor and his book “D-Day- The Battle for Normandy” for the information. Likewise, Wikipedia for information about James Stagg and the weather chart on  https://en.wikipedia.org/wiki/James_Stagg

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