D-Day Operation Overlord Weather Group Captain John Stagg was appointed chief meteorologist to SHAEF in November 1943 to co-ordinate ‘the meteorological arrangements for disseminating weather information and advice to the naval, army, and air forces, US and British under the Supreme Allied Commander’s control. Each of the forces already had its own forecasters, but Stagg’s job was to analyse their predictions and present the overall picture in a succinct form. His deputy was Colonel Donald N. Yates of the USAAF. Stagg travelled to Portsmouth from ‘Widewing’ on Sunday, May 28, where he and Yates shared office space with Admiral Ramsey’s chief weather officer, Instructor Commander John Fleming in a Nissen hut behind Southwick House. Group Captain John Stagg Meteorological requirements for the assault Navy. Surface winds- not exceeding Force 3 (8-12mph) on shore, Force 4 (13-18mph) off shore during D-Day to D+2 (Force 5 bearable in open sea but for limited periods only.) No prolonged periods of high winds in the Atlantic causing substantial swell in the Channel. Visibility- not less than 3 miles. Air Force. Air Transport. Cloud ceiling at least 2,500ft to and over target. Visibility 3 miles at least. Heavy Bombers. Not more than 5/10ths cloud below 5,000ft, cloud ceiling not below 11,000ft over target. Medium and Light Bombers. Cloud ceiling not less than 4,500ft over target, visibility at least 3 miles. Fighters and Fighter Bombers. Cloud base not less than 1,000ft. Bases. Cloud not below 1,000ft. Army. Airborne Landings. Surface wind over target area not to exceed 20mph and not gusty. Half moonlight at least. Ground Forces. Ground dry enough to take heavy vehicles off the main roads. Procedure. January 1944: Directors of Meteorological Service for Air Ministry: Royal Navy, United States Forces and Chief Meteorological Officer at SHAEF began joint consultations. They devised a routine procedure each week for issuing a forecast for a period of five days. i.e. for five days ahead. First conference February 1944 (from mid-April conferences everyday). They found after the first conferences that it was extremely difficult to predict more than 2 or 3 days ahead. During May (when the weather was mainly settled) the experts forecast 18 days on which the weather was suitable for Invasion. Final Conferences Sunday, May 28th. Meteorological report to Supreme Commander that the ‘mainly quiet wind conditions would continue during the coming week’. (Risk of a gale seemed rather small.) Monday, May 29th. Meeting with Supreme Commander etc. At Portsmouth. 1000hrs. Forecast for the five days up to June 2nd. Mainly quiet wind conditions- not more than Force 4- except for wind of Force 5 in western Channel on last two days of the period. Variable cloud conditions average 5/10-7/10 but increasing. Risk of deterioration. Wednesday, May 31st, 0830hrs. ACS/G3 SHAEF (General Bull) was advised that prospects were not favourable for weather after Sunday, June 4th. ‘There were indications that the Azores high pressure area was beginning to show signs of weakness; but no evidence yet that the wind would exceed Force 4.’ Friday, June 2nd, 1000hrs. (With Supreme Commander etc.) ‘ There is now indication that the present that the relatively quiet weather may end Tuesday.’ Winds will be westerly mainly not above Force 4 but Force 5 at times especially in western Channel on Monday 5th, and Tuesday 6th. Cloud conditions-variable-7/10-10/10 early morning. Visibility-moderate to good but risk of fog patches. Friday, June 2nd, 2130hrs. No substantial change. Eisenhower enquired whether improvement likely for the 6th or 7th. Reply-No: in fact danger of Force 5 winds on the 6th. Cloud conditions poor with periods of 10/10 at 1,000ft. Saturday, June 3rd, 0830hrs. Bull was advised: no improvement-risk of Force 5 winds now forecast for Monday and even late Sunday. Cloud forecast uncertain-most likely 7/10-10/10 base 1,000ft. Saturday, June 3rd, 2130hrs. (Supreme Commander etc.) ‘The high pressure area over the Azores is rapidly giving way and a series of depressions across the Atlantic is moving rapidly eastward; these depressions will produce disturbed conditions in the Channel and assault area. Winds will be W-SW, Force 5 on the English coast, Force 3-4 on the French coast from early Sunday until a cold front trough passes. That passage is timed to be sometime on Wednesday, June 7th. From Sunday morning onwards, cloud will be mainly 10/10 with base 500-1,000ft in the morning hours. Visibility will be mainly 3-4 miles but there is a risk of fog spreading from the West up the Channel. After Monday, this risk of fog will decrease. During Wednesday, a front associated with a depression now off Nova Scotia and New England will probably pass through the assault area. Conditions over enemy buses on Monday will, on the whole, be better than over bases in England which were likely to be blanketed with 10/10 cloud at 500-1,000ft.’ Nevertheless, Eisenhower commented that the situation seemed slightly better since the previous night but the experts replied that ‘the balance has now swung too far to the unfavourable side for it to be counteracted.’ Following the presentation of this information the assault was provisionally postponed for 24 hours. Sunday, June 4th, 1415hrs. (Supreme Commander Etc) No new evidence- the only small change is that the front which was expected to clear the Channel areas of low clouds “during Wednesday” is now expected in the first part of Wednesday. Winds will be Force five in the channel from Monday morning onwards: cloud 10/10 at 500-1000ft from Sunday –Tuesday. Postponement confirmed. Sunday, June 4th, 1745hrs. Bull was advised that ‘there has been a substantial change in the situation since the early morning. It is now likely that there will be a fair interval starting about midday today and lasting till about dawn on Tuesday. During this fair interval, and particularly from Monday evening to Tuesday morning, cloud amounts will probably be substantially smaller than given in the forecast this morning: winds will also moderate temporarily, particularly on Monday night and at first on Tuesday. A deterioration will probably set in again during Tuesday; weather on subsequent days will continue unsettled and disturbed.’ Sunday, June 4th, 2100hrs. “Since the statement made before the meeting on Saturday evening, there have been some rapid and unexpected developments in the weather situation over the Atlantic. A front from one of the deep depression in the NW Atlantic has moved much further south than was expected and is now traversing the channel areas. It is almost over Portsmouth now and will clear the eastern Channel, at least on the English side, overnight. When that front has passed there will be an interval of fair conditions which, from evidence we now have, should last at least until dawn on Tuesday”. Wind Speeds by Monday evening should decrease to Force 3-4 on the French coast and cloud will become mainly less than 5/10 with base 2,000-3,000ft. After the interval, lasting until Tuesday morning, cloud will probably increase to 8/10-10/10 from the West during Tuesday afternoon and will continue so over Tuesday night’ ‘Wind will be mainly Force 4 on the English Channel coasts and Force 3-4 on French Channel coasts; in sheltered stretches of the French Channel coast, period of Force 2-3 could be expected. Wind direction throughout will be westerly.’ In reply to Eisenhower, the experts said: ‘Considering the time of the year and the evidence we now have, there is reasonable prospect of the weather slowly improving after Friday if the present trend continues.’ In reply to Leigh-Mallory, they said that ‘good though not uninterrupted conditions for visual bombing for heavy and medium bombers could be expected from Monday evening till early forenoon Tuesday.’ Provisional instruction given for assault on Tuesday, June 6th. Monday, June 5th, 0415hrs. No substantial changes in information given at previous evening’s meeting. ‘The fair interval had now begun in Portsmouth and will probably last into the forenoon of Tuesday. During this interval, cloud will be mainly less than 5/10 with base 2,500-3,000 ft. Wind on the beaches in the invasion area will not exceed Force 3 in this interval and will be westerly. Visibility will be good.’ ‘During Tuesday, clouds will very probably increase again, from the West, giving a period of overcast sky with cloud base at about 1,000 ft in the assault area later in the day. These cloud conditions will continue overnight Tuesday-Wednesday. Winds will be westerly Force 4 on the English coast and mainly Force 3 on the French coast’ ‘Conditions will probably continue unsettled after Tuesday and it is difficult to time the changes... The situation even after Wednesday must continue to be regarded as disturbed: a quiet settled spell cannot be expected to start immediately after such an intensely disturbed situation. But the time of year suggests that changes after Wednesday may be expected to be in the direction of improvement rather than renewed and further deterioration to the present intensity.’ Following this presentation, the final and irrevocable decision was made to launch the assault on Tuesday, June 6th. Group Captain J.M. Stagg Notes on report to SCHAEF, June 22, 1944
Ramsay ‘Admiral Kirk must be told within the next half hour if “Overlord” is to take place on Tuesday. If he is told it is on and his forces sail and are then recalled, they will not be ready again for Wednesday morning; therefore a further postponement would be for 48hrs.’ Eisenhower ‘Conditions are almost ideal up to a point, even if the operations of the heavy air may be held up later. Suppose you (to ANCXF) give orders tonight that Tuesday is on; should we meet again in the morning?’ Montgomery ‘The only decision the weather experts could give at 0400hrs tomorrow would be the position of the next depression.’ Smith ‘Looks to me we’ve gotten a break we could hardly hope for.’ Leigh-Mallory said he thought it would be likely to be only a moderate night and that Bomber Command would have great difficulty in getting their markers down and in doing useful bombing. This brought the response from several members present that ‘You are referring to another day, in fact you are a day out.’ L-M’s statement brought the following response from the Supreme Commander-‘Don’t be that pessimistic.’ Smith ‘Our apprehension now concerns spotting for Naval gun-fire and the second mission for the heavies. It’s a helluva gamble but this (The decision to go ahead) is the best possible gamble.’ Tedder mentioned that it would be a question of making best use of the gaps between the trailing fronts brought along by the series of ‘lows’. ‘Agree with L-M, the operations of heavies and mediums are going to be chancy.’ Eisenhower ‘We have a great force of fighter-bombers.’ (To Montgomery) ‘Do you see any reason for not going on Tuesday?’ Montgomery ’I would say – Go!’ Eisenhower ‘The alternatives are too chancy. The question, just how long can you hang this operation on the end of a limb and let it hang there. The air will certainly be handicapped.’ Leigh-Mallory ‘Hell of a situation if the German night bombers can operate and our night fighters cannot get off. At Dieppe...’ Eisenhower ‘If you don’t give the instructions now, you cannot do it on Tuesday.’ Tedder (To Leigh-Mallory) ‘If the later forecast shows a deterioration earlier (i.e. during Tuesday night), putting on the night bombers at an earlier might be considered.’ Eisenhower ‘Well, I’m quite positive we must give the order; the only question is whether we should meet again in the morning?’ ‘Well, I don’t like it, but there it is.’ ‘Well boys, there it is, I don’t see how we can possibly do anything else.’ Southwick House 2130 Hours, Sunday, June 4th, 1944 Memo by Air Vice-Marshall James Robb
Monday, June 5th, 0815hrs: Up at 7.30 and back to Southwick for breakfast and personal talk with Dunstable before speaking to General Bull. I got Harding just going off duty. He confirmed that no major change in ideas had taken place at Dunstable since 0300hrs. Except that they now thought that Tuesday’s warm front may be deferred to Tuesday night. 0845: Phoned General Bull and told him we stuck to our story given at 0415: I added that information from France showed that the front which was passing Portsmouth between 2200 and midnight last night was covering the assault area hinterland during most of the night and that 10/10ths low cloud was the accompaniment. When we got back to lunch, the sky was 10/10ths, some of it very low, 800-1,000 ft it seemed, and wind force up to 5-6. What the mischief was going wrong? I got in touch with Dunstable: Douglas said we must expect 10/10ths late evening and some cloud up to 5/10ths persisting in the target areas. The air unstable with inversion at 7,000 ft cumulus spreading out and filling the sky: there would not be much dissipation until dusk but it would break up. I felt slightly assured. 1930 Conference: Still conflict between Dunstable and ‘Widewing’. Krick holds for less than 5/10ths overnight while Petterson and Douglas hold for continuing cloudiness up to 10/10ths at times interspersed with fair breaks. The SC and Admiral Creasy come into office before the conference worried about the 10/10ths cloud and high wind (it was still Force4-5). ‘What do you think Stagg?’ said Eisenhower. ‘I hold to my forecast, Sir, breaks after dark tonight.’ He clapped be on the shoulder and said, ‘Good, Stagg, hold to it’, and went out smiling. 2100 Conference: (It continues 10/10ths with only very slight breaks; the wind has gone down.) A long dreary conference. I was too tired to concentrate: finished at 11pm the upshot was to accept a cloudy picture. But when Yates and I went to see General Bull at the War Room at the Command Post we stuck to our early forecast. Light winds; breaks tonight. We waited in the War Room for news of recce flights. Any reliable reports we got showed the same conditions likely over there. To bed at 1am still cloudy but calm. Excerpts from the diary of Group Captain J.M. Stagg June 1944
http://www.bbc.co.uk/news/uk-scotland-27237226 The weather forecast that changed D-Day It has been called the most important weather forecast of all-time. In June 1944 thousands of Allied troops would land at five sites across France in the largest amphibious invasion ever. The ambitious plan, entitled Operation Overlord, would see over 160,000 troops being deployed in what would prove to be one of the decisive actions of the conflict. Despite months of meticulous planning, there was one aspect that military commanders could not fully legislate for and which would play a crucial part in deciding whether the massive invasion would succeed. The weather. Due to the size and logistics of the operation the invasion could only be launched on certain days, each of these days providing a small window of opportunity to launch the massive mobilisation of Allied forces. A team of meteorologists would advise Operation Overlord's overall commander, Gen Eisenhower, on when would be the correct time to launch the invasion and help decide the fates of thousands of soldiers' lives. Forgotten hero Now, a new play running at the Royal Lyceum Theatre the aims to tell the story of Scottish meteorologist James Stagg's role in the historic invasion. Pressure tells the true-life story of Scottish meteorologist James Stagg who had to advise Gen Eisenhower on when conditions would be suitable to launch the invasion. Group Captain Stagg helped persuade the operation leaders to delay the launch of the operation by a week to allow the weather to improve. He did this despite being put under pressure from senior Allied military figures, who felt that any delay could impact on an element of surprise which was seen as being essential to the operation's success. The decision to delay proved to be the correct one and one which saved thousands of soldiers' lives. 'A complex character' The play has been written, and stars, David Haig. The actor has has previous experience in writing for the stage when he wrote and starred in the play My Boy Jack, which featured Harry Potter actor Daniel Radcliffe. The versatile actor said writing the story had taught him how to script, and play a complex character. He said: "I've learned that slow burning characters are the most interesting. "He (Stagg) had a superficial veneer of reserve and seriousness but underneath he had an integrity and honesty which hopefully evolves through the play." Performing in front of a Scottish crowd has presented a unique challenge for the actor, which he did not fully realised before he made the decision to star in the play. He joked: "I'm speaking in an Edinburgh accent on stage in front of hundreds of people... no pressure there I suppose." The production is directed by Lyceum Associate Artist John Dove and is set to run at the Royal Lyceum Theatre from 1 May to 24 May before it moves for a residency at the Chichester Festival.
David Haig was interviewed on BBC's Front Row about the play, which sounds interesting Of course they tried to make out that Stagg's story was hitherto unknown-that is unless you've read any book or watched just about any film or documentary about D-Day of course!
Gp Capt Stagg published his own account in the book ' Forecast for Overlord' in 1971, I have an ex public library copy in my collection. The sequence of synoptic is interesting and they highlight just how brave the decision to go was.
Good thread this and takes you back to the time Andy posted some interesting stuff before he lost his way..
Or read Miles Foden's "Turbulence"... or watched "The World At War"... Were I a commissioning editor for TV documentaries (I am available for hire....) I would chuck out anything titled "The Secret..." "The Hidden..." "The Unknown..." and think awhile on anything called "The Forgotten...." Which means I won't be getting a job on Channel 5 any time soon. Radio 4, hang your head in shame.
