Weather forecasting for Operation Overlord
Stagg was a "dour but canny Scot.. "[1] He had been given the rank of group captain in the RAF "to lend him the necessary authority in a military milieu unused to outsiders".
[2] The senior commanders were General Bernard Montgomery, Admiral Sir Bertram Ramsay and Air Marshal Sir Trafford Leigh-Mallory, plus Eisenhower's deputy, Air Marshall Arthur Tedder, his chief of staff Walter Bedell Smith and his deputy chief of Staff Major General Harold R.
British general Frederick Morgan (head of COSSAC) had half-jokingly said to him "Remember, if you don't read the runes (or signs) right, we'll string you up from the nearest lamppost".
[7] The American team was based at the USAAF facility Widewing used for SHAEF HQ at Camp Griffiss in Bushy Park near Teddington.
Landings had to be at about the same time on all beaches to avoid later arrivals meeting an alerted enemy, and Omaha had an exposed tidal flat of 300 yards (275m) to cross.
[28] The first coded messages (about 160; repeated on the 2nd and 3rd ) over the BBC's Radio Londres told the French Resistance that the invasion was expected in two weeks, e.g. the quote from Paul Verlaine's 1866 poem Chanson d'automne (sung by Charles Trenet): Les sanglots longs des violons d'automne ("The long sobs of autumn violins").
Commander's meeting at which main topic was the change for the worse in weather, affecting air (operations) generally and the carriage of airborne troops in particular."
He followed his instincts, overlooking the optimistic American team, saying "The whole situation from the British Isles to Newfoundland has been transformed in recent days and is now potentially full of menace".
Some officers glanced out the window at the beautiful sunset in slight bewilderment (on Double British Summer Time, it was still light; France was an hour behind).
He said to the commanders at 21:30 hours "Gentleman, the fears my colleagues and I had yesterday about the weather for the next three or four days have been confirmed" and gave a detailed forecast of rough seas, winds up to force six and low cloud.
Convoy U2A from Salcome and Dartmouth left on 4 June for Utah Beach but did not receive the broadcast recall notices, and was headed for France alone (panic in Southwick House ops room!).
[39] At the 21:00 (9 pm) meeting rain and wind was battering the windows but Stagg said "Gentleman, since I presented the forecast last evening some rapid and unexpected developments have occurred over the North Atlantic".
Ramsay made it clear that if Overlord proceeded on Tuesday he would need to issue provisional warnings in the next half-hour, but if they restarted and were recalled again there was no question of continuing on Wednesday.
[40] Ramsay wrote that "we decided to take a chance and go ahead; while the grounds were not good it seemed to be Tuesday – or not this week at all" and Eisenhower said "I'm quite positive we must give the order.
Ramsay noted 'this time the prophets came in smiling, and Hogben mused "I was scared of getting it wrong ... we knew we were making history".
Montgomery and Major General Walter Bedell Smith, Eisenhower's chief of staff, were eager to launch the invasion.
Admiral Bertram Ramsay was prepared to commit his ships, while Air Chief Marshal Trafford Leigh-Mallory expressed concern that the conditions would be unfavourable for Allied aircraft.
[42][46][47][48] At mid-day Eisenhower was playing a game of draughts in his trailer with his aide Harry Butcher; he was losing, but at 12:30 pm he managed a draw, which he saw as a good omen.
[30] The Verlaine message (intercepted at 9:33 pm) went to OKW in Berchtesgaden, but stopped on Jodl's desk; he distrusted the source (Helmut Meyer at 15th Army HQ in France) and did not send out a general alert.
Von Rundstedt in Paris thinks that there is no immediate prospect for the "Grossinvasion" and at 10 pm when General Blumentritt tells him that Fifteenth Army Intelligence (now under the SS) has received the second line of the Verlaine poem, he said that Eisenhower would not announce the invasion over the BBC and to pass it onto OKW and to Blaskowitz but not to order a general alert of the two armies along the coast: "No, especially not in this weather".
[58] Canadian troops landed on Juno Beach at 7:45, delayed from 7.35 by heavy swell and poor visibility; the amphibious tanks arrived 15 minutes after the infantry.
[60] The BBC announced that Allied Armies have started landing "on the northern coast of France" at 9:32 am, Read by John Snagge, the actual location was not given.
[62] Had Eisenhower postponed the invasion, the next available period with the right combination of tides (but without the desirable full moon for airborne troops) was two weeks later, from 18 to 20 June.
All we knew was that there were several storms blowing across the Atlantic towards us, any one of which would have whipped up the waters where the fleet was gathering, and provided unwelcome cloud over Normandy".
[67] In 2020, Maureen Flavin Sweeney was acknowledged by the United States government for her role in weather forecasting from Blacksod which directly influenced the schedule of the operation.
Sweeney's weather report from the 3 June 1944 showing rapidly decreasing pressure, led to the delay of the landings by 24 hours by Eisenhower.
Unbeknownst to Sweeney, the hourly weather reports she sent to the Irish Met Service from the post office she worked as an assistant were forwarded to Allied Expeditionary Force in England.
As the Luftwaffe meteorological centre in Paris predicted two weeks of stormy weather, many Wehrmacht commanders left their posts to attend war games in Rennes, and men in many units were given leave.
[73] When Rommel consulted meteorologist Major Heinz Lettau at Army Group B he was advised that there could be no invasion in the next two weeks because of the weather.
He discussed by phone on the 4th with meteorologist Major Hermann Mueller at von Runstedt's headquarters in Paris who had data suggesting that an airborne operation would be possible and a seaborne landing conceivable although Channel conditions were far from ideal.
