D-Day could have been a total failure but for the forecasting and diplomatic skills of an RAF meteorologist. American and British weather forecasters had disagreed about the weather they expected on the Normandy beaches and in the English Channel on 5, 6 and 7 June 1944. Eisenhower and Churchill needed to know. Group Captain John Stagg (RAFVR) had to make the call.
Senior Meteorologist Group Captain J M Stagg RAFVR. © Met Office/Crown.
On the early morning of June 6, 1944, history witnessed the largest seaborne invasion ever as Allied forces stormed the Normandy beaches. Operation Neptune, part of Operation Overlord, commenced with over 100,000 troops from Britain, America, and Canada making their way ashore along a 50-mile stretch. The success of this critical mission hinged not only on military strategy but also on favorable weather conditions.
The invasion was originally planned for June 5, but the entire invasion depended on a forecast of acceptable weather. The allied commanders’ basic wish list of conditions for the invasion were:
• Quiet weather for 48 hours before D-Day to allow the assault convoys to sail from their base harbours and form up and three subsequent days of weather of Beaufort Force less than force 4.
• Less than 30% cloud cover below 8,000 feet (2,400 metres) with a minimum cloud base no lower than 2,500 feet to enable aircraft carrying parachutists and tugging gliders to deploy, and visibility more than three miles (5km).
• Low tide at dawn on D-Day itself.
• It should be between one day before and four days after a full moon.
Choosing the right date was crucial to synchronise with the Soviet summer offensive in the east, maximising pressure on German resources. After ruling out May due to logistical constraints, General Eisenhower, the Supreme Allied Commander, considered June. However, the odds of finding suitable weather conditions were slim—approximately 13 to 1 and even more challenging with the requirement of a full moon.
Group Captain James Stagg, a senior meteorologist at the British Meteorological Office, played a pivotal role in advising Eisenhower on the weather forecast. He coordinated with American and British meteorologists, considering their differing opinions and collaborating to reach a consensus. Providing a five-day forecast was a formidable task, given the limited forecasting capabilities of the time. Nevertheless, Stagg’s accurate advice was crucial for the invasion’s success.
A Mustang of II (Army Cooperation) Squadron is prepared for a mission over Normandy as part of Operation Overlord. © MOD/Crown
Initially, the forecast for June 5 seemed unfavorable, leading to a provisional postponement. However, a glimmer of hope emerged on June 4, suggesting a brief period of fair weather starting on the night of the 5th. The meteorologists agreed that a short-lived high-pressure system would bring acceptable winds and cloud conditions, albeit far from ideal. Stagg’s briefing confirmed fair weather on the morning of June 6, with the possibility of extending into the afternoon.
Although conditions were not perfect, Eisenhower made the final decision to proceed with the invasion on June 6. The first convoy departed in the early hours, facing challenges from cloud cover, missed drop zones for parachutists, and strong onshore winds. Despite these obstacles, conditions gradually improved throughout the day. The German commanders, unaware of the approaching invasion due to successful British deception plans and the bombing of radar stations, did not trigger their warning system.
The accurate weather forecast provided by Stagg and his team played a crucial role in achieving the element of surprise and saving countless lives. In retrospect, postponing the invasion until the next suitable tides, two weeks later, would have resulted in catastrophic weather conditions. The forecasters’ expertise and ability to make critical decisions under intense pressure proved to be one of the most important forecasts in history.
Without the sophisticated technology and forecasting models available today, the D-Day meteorologists demonstrated remarkable skill and resourcefulness. Their contribution, alongside the brave soldiers who landed on the Normandy beaches, ultimately changed the course of World War II.
Winston Churchill with General Eisenhower in Normandy just after D-Day, June 1944. © Alamy / Fremantle.
Air Mail
This article has been adapted from the October 2022 edition of Air Mail magazine which looked at RAF meteorology. To receive Air Mail, which is the RAF Association’s quarterly members’ magazine and looks at all aspects of the RAF’s work, now and since it was founded, become a member and opt for Air Mail as part of your membership.
