The Forecaster: The Man Who Decided D-Day

Planes on their way to the Normandy beaches

May 15 1944, Hammersmith, London (D-Day -21)

One by one, clutching the beautifully engraved invitations they had received a month earlier, they all filed into St Paul’s School in Hammersmith. Every invitation was carefully inspected by military policemen, every identity card checked. Admirals, Generals and Field Marshals received the same level of careful scrutiny as the lowliest staff officer.

With barely a murmur, the men who together represented the highest ranks of the Anglo-American conclave filtered into the school’s auditorium. The sense of anticipation was practically palpable.

At 10am precisely, General Dwight D Eisenhower, Supreme Allied Commander in Europe rose to speak.

“I welcome you,” Eisenhower said, “on the eve of a great battle.”

Two years previously, Ike reminded them, he had been charged with a mission — to plan and carry out the Allied invasion of Europe. It was a herculean task, one that would require a combined air, sea and land assault the likes of which the world had never seen. But finally, he told the audience, after months of planning and preparation they were ready to do it. OVERLORD would begin on June 5th 1944.

Eisenhower handed the briefing over to General Bernard “Monty” Montgomery. Four armies, Monty explained, would assault the Normandy area of France. This presented the best compromise between distance, terrain and likelihood of success. The Pas de Calais was nearer, certainly, but it was also where the German forces, commanded by Erwin Rommel, most expected an assault to come. This didn’t mean that Normandy was undefended — far from it — but it was hoped that by means of deception and guile the Allies could persuade the enemy that the attack on Normandy was merely a diversion, with a larger attack to follow in the Calais area. This would hopefully encourage the Germans to hold back from reinforcing the Normandy defenders, buying the Allies time to consolidate their position.

Using the maps and models that littered the room Montgomery went on to explain in detail the form that the initial attack would take. In the early hours of D-Day, a massive airborne assault would be launched along a wide stretch of the Normandy coast. Assisted by the French Resistance, SOE and the SAS, British and American paratroopers would blow up vital positions and seize critical bridges and towns in an effort to disrupt the German ability to respond to the coming attack. At dawn, a huge amphibious assault comprised of both infantry and armour would be launched along a fifty-mile front. Five beachheads — two American, two British and one Canadian — would be seized, whilst the combined navies of the Allied powers provided fire support from out at sea. Meanwhile, in the air above, Allied fighters would assert air supremacy preventing the Luftwaffe from interfering and Allied bombers would attempt to knock out German defences and reinforcements.

“Rommel is an energetic and determined commander.” Montgomery asserted, remembering his old desert rival, “He has made a world of difference since he took over. He is best at spoiling attack; his forte is disruption… He will do his best to Dunkirk us.”

They needed to get men off the beaches quickly, Montgomery stressed, get them reinforced and get them linked up with the airborne troops before those units became isolated. If they could do this — if they could avoid Rommel throwing them back into the sea — then the Allies had a chance.

His points made, Montgomery yielded the floor. Over the next few hours, more briefings were given and questions raised and answered. With that, the time for talking was over. The time for action was about to begin.

May 28 1944, SHAEF Advanced Headquarters, Portsmouth (D-Day -8)

Group Captain James Stagg was a worried man.

Group Captain James Stagg

At 39 Stagg had — until recently — been one of the rising stars at the British Meteorological (“Met”) Office. Stagg had started as a junior assistant at the observatory at Kew then gone on to manage various facilities and field offices. He’d also led polar and desert expeditions and was a geophysicist of some repute. Now he was Chief Meteorologist to the Supreme Headquarters Allied Expeditionary Force (SHAEF)

His appointment in November 1943 had caused a certain amount of controversy. As a geophysicist he wasn’t, strictly speaking, a weather forecaster himself and this had caused a considerable amount of grumbling from the genuine forecasters to be found in the British and American forces.

More importantly at the time of his appointment, he was still a civilian. This had gone down so badly with some in the high command that General Harold Bull, SHAEF’s Deputy Chief of Staff, conspired to have Stagg removed from his position. He wanted an American officer— Lieutenant-Colonel Donald Yates — appointed in his place.

Lieutenant-Colonel Donald Yates

For both Yates and Stagg this had been an awkward situation. By the time General Bull made his move Yates had already started working as Stagg’s deputy. Both men respected the other for the different talents that they brought to the table. Stagg’s demotion however was soon reversed. The British Air Ministry, who ultimately controlled the Met Office, were outraged at his dismissal so played their trump card.

When SHAEF was formed, they pointed out, it had been agreed that the Chief Meteorologist should be British, because a British Meteorologist would have a better feel for the nuances of Northern Europe’s ever-changing weather systems. Stagg was immediately mobilised into the RAF as a Group Captain, neutralising the General’s objections, and his command position restored.

None of this was what worried Stagg right now though. What worried him was the bloody weather.

May 28 1944, Senior Commander’s Briefing, Portsmouth (D-Day -8)

As Stagg prepared to deliver his daily briefing to Eisenhower, he thought about what the Supreme Commander would be hoping to hear. With only eight days to go until 5th June — D-Day — Ike and his staff would be looking for confirmation that the weather was going to be acceptable.

Just what “acceptable” meant in this context had taken Stagg and his staff months to work out. Every element of the combined amphibious assault brought different, complex weather restrictions into play.

The navy, for example, said that surface winds could not exceed Force 3 onshore or Force 4 at sea. Any more than that and the flat-bottomed landing craft carrying the infantry would be driven off course or swamped. The first wave of tanks, which were to be floated ashore from 5000 yards out using inflatable side-panels, would also likely flounder.

This wasn’t their only requirement. The tides also needed to be just right to allow mines and obstructions to be cleared. They also needed visibility of at least three miles if the battleships, cruisers and destroyers assembled offshore were to be used as artillery support. Finally, to have any hope of supplying and reinforcing the beachheads they needed the wind to remain low for at least D-Day +1 as well.

The demands of the air force were even greater. Fog in Britain would ground their planes completely and heavy clouds would cause a whole variety of problems. The fighters and fighter bombers needed a cloud base of no less than 1,000ft, whilst the medium and light bombers tasked with neutralising gun emplacements during the landings needed both visibility of three miles and a cloud ceiling not less than 4,500ft. The heavy bombers meanwhile, which were intended to disrupt German reinforcements and destroy infrastructure, ideally needed no more than 5/10ths cloud cover below 5,000ft and a cloud ceiling not below 11,000ft.

The list of demands didn’t stop there. Both air force and army agreed that for the transport aircraft carrying the paratroopers to find their targets they’d need at least a half-moon and a cloud ceiling of 2,500ft over their targets. Winds could also not exceed 20mph (roughly Force 5) or the paratroopers would be unable to jump. The gliders had similar limitations. Finally, the army pointed out, they needed the weather to be dry during and after the landing (without significant rain beforehand) else the roads and beaches would quickly become unusable.

Comparing these collected requirements with historic weather patterns in the Channel was, in part, what had led Stagg and Yates to originally inform Eisenhower that May, June and July represented the best hope for suitable conditions. May was too soon for Ike’s assembling forces though, so this meant a June invasion. Only two short periods in June would provide the right tide and lunar conditions though: June 5th — 7th and June 19th — 21st. If the weather failed to cooperate then the invasion would have to be pushed back until July, giving Rommel more time to prepare his Atlantic Wall and providing more opportunity for German Intelligence to determine both the day and the location of the assault.

Stagg finished updating the Supreme Commander on the current weather conditions — quiet and dry — and waited for the question he’d been dreading. He dreaded it because he knew that he didn’t have an answer. Yet it was one Eisenhower had begun asking daily.

“What’s the long term forecast, Stagg?” The General said immediately, watching his Chief Meteorologist carefully.

“I don’t have one yet, sir.”

May 29 1944, the Weather Hut, Portsmouth (D-Day -7)

Stagg sighed. The argument they were having right now was one of the reasons he was unable to provide Eisenhower with any certainty. On the end of the secure conference call were the three main weather centres to which he had access: ‘Widewing’, ‘Dunstable’ and the Admiralty…

…and they could not agree about the weather.

Widewing were the Americans, based in Eisenhower’s old headquarters in Bushey Park, London. Technically, Widewing was Lieutenant-Colonel Yates’ Command, but with Yates down in Portsmouth supporting Stagg the brash and charismatic Irving Krick effectively headed the team there.

Dunstable were the British. More specifically, the Met Office. Their nickname was a reference to the fact that the organisation had moved out of London during the Blitz and were still temporarily based in the small town of that name to the north of the capital. When Dunstable talked it was normally via the measured tones of Norwegian meteorologist Sverre Petterssen.

The Admiralty were the third and final weather centre. They were largely concerned with sea, swell and surf forecasting rather than weather specifically, but to do so the Royal Navy had amassed its own team of meteorologists and an awful lot of experience over the centuries. For that reason, they were considered worthy of a place at the meteorological table.

All three weather centres had access to the same extensive dataset, provided by the network of weather stations that criss-crossed Britain, Greenland and Ireland, as well as the various ships and planes in the Atlantic tasked with reporting on the weather. All three, however, were free to reach their own conclusions as to what that data meant.

Stagg’s problem was that Widewing and Dunstable had become locked in an increasingly fractious debate, triggered by Eisenhower’s request for a long term forecast. Put simply, Widewing had one, but Dunstable refused even to attempt one.

The problem of predicting the weather

Such an extreme difference in opinion may seem difficult to understand, especially between two parties with access to the same data. But in 1944 weather forecasting was still more of an art than a science, and Krick and Petterssen represented two very different ideological schools of thought as to how that art should be prosecuted.

Irving Krick

Krick believed that weather systems were entirely consistent and predictable. In fact, he had become a meteorologist with the goal of using that consistency to make money. He had become convinced that predicting long term weather patterns for American businesses would make him a wealthy man, and he had been working towards furthering that end when war intervened. A ruthless self-promoter and charismatic speaker, he had convinced many both in the US Army and outside of it that he — and only he — could provide accurate weather forecasts.

To do this he largely used the ‘analog method.’ This meant taking the current data and finding the closest possible match for that data in the past. This, he believed, would tell you not only what the weather would be like that day, but also what the weather would be like on the days immediately after — because it would be entirely consistent with that it had been like before.

Sverre Petterssen

Petterssen, by contrast, thought that predicting the weather over a long period of time required a level of scientific knowledge and data analysis that no one had yet managed to achieve. This was not to say that Petterssen was entirely pessimistic about mankind’s ability to predict the weather at all, simply that he felt that any forecasts would always be based on an incomplete understanding of the complex systems that powered the world’s weather. So, with data and experience, you could make forecasts, but they would only be accurate in the short term — just a few days at the most.

Indeed Petterssen believed that Krick’s methods were not just dubious, but downright misleading. He hadn’t been afraid to tell Krick that either, which hadn’t exactly improved cross-departmental relations.

Gentlemen.” Said Stagg, sharing a weary look across the table with Yates, “Can we perhaps for now just agree on what the numbers mean for today?”

On this at least Stagg was able to find some agreement. The weather was still good, with a small risk of deterioration.

“Possible or not possible?”

At that evening’s briefing, Eisenhower pressed him again for a long term forecast. How was Monday, June 5th looking?

“Possible or not possible?” he asked.

Stagg found himself squirming yet again for an answer.

“At this time of the year,” he reluctantly conceded, “continuous spells of more than a few days of really stormy weather are infrequent. If disturbed weather starts on Friday it is unlikely to last through both Monday and Tuesday; but if it delayed to Saturday or Sunday the weather on Monday and even Tuesday could well be stormy.”

Stagg stressed that this answer was based purely on generalising the weather so far in May — not on any specific data — but the assembled commanders seemed happy nonetheless. Stagg, however, could not shake the feeling that there was little real value to be found in his statement at all.

Same day. Task Force 24, Coast of Greenland (D-Day -7)

Admiral Edward “Iceberg” Smith was proud of his nickname. He’d earned it. He’d been at sea almost continually since he was 23 years old and for most of that he’d been in or around the arctic circle.

At first it was with the US Coast Guard, patrolling icy waters for ships in trouble, carrying out scientific missions and filing weather reports. When America had entered the war, however, he’d suddenly found himself in the navy. The job was still mostly the same, he mused, although there were some differences. For one thing, taking pot shots at German infiltrators trying to set up secret weather stations on Greenland was now a regular feature on his “to do” list. He also got to call himself ‘Admiral’.

Mostly though, he still spent his days out here watching the weather.

“Ready to report sir.” Said a young officer at his side, indicating that the latest weather readings could now be transmitted.

Admiral Smith nodded his approval.

The weather was changing for the worse, he thought, he could feel it in his bones.

May 31 1944, the Weather Hut, Portsmouth (D-Day -5)

Stagg frowned. He hadn’t been able to host the day’s conference call with the weather centres himself so Yates had taken his place. What the American was telling him now though just didn’t seem to make sense.

Over the last two days, reports and data from aerial patrols and Task Force 24 had begun to filter in and to Stagg none of it looked good. The opposite in fact. Bad weather was coming.

If this were true, then it was bad news indeed. If bad weather hit on Sunday it was unlikely to clear up for D-Day and that meant postponement. Yates had told Stagg that Dunstable agreed with that assessment, as did the Admiralty. Both were now forecasting a black weekend.

What was puzzling though was that Widewing disagreed entirely. According to Yates, Krick and his team had argued vehemently that the weather would improve. The coming weather front, they insisted, would traverse the Channel very rapidly and clear quickly. The invasion could go ahead.

Luckily, with Eisenhower locked in the final preparations for the invasion, Stagg’s next briefing with the Supreme Commander had been postponed until Friday. Stagg firmly believed that bringing two radically different views on the unfolding weather in the Channel to the General would be disastrous. He desperately hoped there that the centres would come to some kind of agreement before then.

June 2 1944, Blacksod Point, Republic of Ireland (D-Day -3)

Roughly 500 miles from Normandy on the west coast of Ireland stood Blacksod Point. Although technically neutral, since 1939 a secret treaty had existed between the Republic of Ireland and the United Kingdom allowing for the sharing of weather data. As the furthest western land-based weather station in the British and Irish Isles, this had suddenly made Blacksod Point lighthouse one of the most important locations in them.

Blacksod Point. Photo by Evita-Coyle.

This was all unknown to Tom Sweeney, Coast Guardsman and lighthouse keeper, as he made his latest set of weather readings. The barometer was dropping, he noted. Bad weather was coming.

Having jotted down his results he made the short walk over to the village post office — the only place with a phone — so he could file them. Whilst that might seem inconvenient, Tom didn’t mind. He knew Maureen Flavin would be on duty and, although he hadn’t worked up the courage to tell her yet, Tom was in love.

Later that day, the Weather Hut, Portsmouth (D-Day -3)

The sun had not even risen by the time Stagg and Yates entered the Weather Hut that morning. As the first of the day’s weather reports began to come in, they looked for some evidence for Widewing’s continuing insistence that the weather on D-Day would be fine.

They didn’t find it.

“In all the charts for the last 40 or 50 years I had examined,” Stagg wrote later, “I could not recall one which at this time of year remotely resembled this chart in the number and intensity of depressions it displayed at one time.”

It wasn’t just the weather ships in the Atlantic now that were reporting the coming inclement weather either, as the reports from Blacksod Point showed.

Yet a few minutes later, on the morning conference call, Widewing refused to modify their forecast. Indeed not only did they cling fast to their belief that high pressure was building, but also now insisted that this would buffer the Channel entirely from the approaching lows and their fronts.

On the other end of the phone, Dunstable were livid. What about the fall in barometric pressure reported by Blacksod Point? Petterssen demanded. How could that be ignored?! This suggested not only that bad weather was coming, but that on 5th June Force 5 winds and low-lying cloud would stream over the landing beaches. This was a potential disaster in the making.

Widewing insisted that Blacksod Point’s data was either faulty or an outlier. They refused to modify their forecast.

The continuing division placed Stagg in an enormously difficult position, especially as the Admiralty refused to make any prediction at all.

Stagg remained convinced that a divided opinion would be worse than useless. He knew he wasn’t the only one who felt that way. Somehow General Bull had gotten wind of the lack of agreement the day before. He had taken Stagg aside after a meeting for a quiet word.

“For heaven’s sake Stagg” Bull had said, more in worry than anger, “get it sorted by tomorrow morning before you come to the Supreme Commander’s conference. General Eisenhower is a very worried man.”

Stagg knew that Eisenhower’s worry stemmed from the fact that in order to meet the 5th June target date, now barely sixty hours away, the General had already begun to order his men and supplies to leave their bases and head to their embarkation points. Soon ships from ports as far away as Belfast and Scapa Flow would begin to move south to take part in the assault.

Both Eisenhower and Stagg were running out of time.

As Stagg prepared for that morning’s briefing, he realised that he might be forced to do something he didn’t want to do — pick a side.

Same day, Senior Commander’s Briefing, Portsmouth (D-Day -3)

The weather, Stagg told Eisenhower, was continuing to deteriorate. It was still impossible to predict accurately what conditions would be like on Monday and Tuesday, but the signs were that winds may be as high as Force 5 and the clouds low.

Eisenhower and his staff took the news without comment. They agreed to reconvene and discuss things further that evening.

Stagg avoided Yates’ gaze throughout the meeting. The two men had argued heatedly on the way over about whether they should reveal that the weather centres were divided in opinion. Yates insisted that Eisenhower and the others needed to know. Stagg overruled him and reluctantly Yates had agreed to comply.

As they left the meeting, Stagg made his excuses and broke away on his own. He needed time to think.

“Was it fair to the Supreme Commander to withhold the cleavage of opinion from him?” He wrote later when describing that lonely walk. “Yes. I argued with myself: ‘General Eisenhower has big enough problems of his own… We have no brief to make his task more arduous than it manifestly is.’”

The problem, Stagg realised, wasn’t just the lack of consensus. It was that he firmly believed, based on his own experience, that Widewing were wrong. For now, with the Admiralty refusing to take a position, he could at least argue that his own opinion plus that of Dunstable represented a majority view of sorts. If the Admiralty’s view shifted, however, then he would be forced to either side with the minority view, or deliver a forecast that he firmly believed would lead to catastrophe in the Channel.

Stagg was also worried about Yates. He trusted his second-in-command completely, but he knew that he was placing him in an increasingly difficult position. Widewing was Yates’ command, and he knew that the American both trusted their ability and felt duty bound to support them as their commander. Right now Stagg was asking him not only to go against that, but to trust in Stagg’s belief that they must present a consistent world view. It was an enormous ask of the man, one that grew larger by the day.

Pushing these thoughts to one side, Stagg returned to the weather hut. Dunstable had indicated they would be pushing for new data before another conference call that afternoon. Stagg wanted to spend as much time as possible running the numbers and trying to come up with a plan.

That Evening, the Weather Hut, Portsmouth (D-Day -3)

That evening, things got even worse for Stagg. As he listened, the Admiralty admitted that they now believed that Widewing might be partially correct. The high-pressure area that Widewing were so insistent would protect Normandy wouldn’t do so entirely, the Admiralty claimed, but they thought it might do enough to mean that only light cloud would cover the area.

Dunstable (and Stagg) were horrified. There were three depressions heading this way, Dunstable insisted, heading over the Atlantic past Ireland. The data suggested that these would develop over Scotland and sweep in with wind, cloud and rain that would mask Normandy right at the time the airborne troops were trying land and while the invasion fleet was at sea.

Stagg’s worst case scenario had happened. He firmly believed that Dunstable were right, but it was now two against one. Widewing and the Admiralty believed the invasion could go ahead. Dunstable disagreed. Across the table, meanwhile, Yates remained ominously silent.

For an hour and a half, the debate raged. No consensus emerged. In the end both Yates and Stagg had to sprint to make their evening briefing with Eisenhower.

In that meeting, Stagg made his choice and picked a side. He told Ike and his staff that the situation was unchanged. Stagg insisted that it was still impossible to make a call, but that it was more likely conditions would deteriorate than improve. As a noticeably uncomfortable Yates looked on, Stagg agreed that tomorrow he would provide a go/no-go forecast for D-Day.

After the meeting, Stagg went for another walk to clear his head. As he returned to the Weather Hut he overheard Yates on the phone to Widewing. Yates was begging them to ring Dunstable before tomorrow’s conference call and resolve their differences. From Yates’ reactions it was clear that Krick had no intention of doing so, but after much pleading Yates did manage to secure one vital concession — tomorrow Widewing would agree to accept, and back, Stagg’s decision on whether they should advise Eisenhower to postpone D-Day. Even if it conflicted with their own opinion.

That evening, as Stagg was heading to his quarters, he bumped into Lieutenant-General Morgan, Eisenhower’s Deputy Chief of Staff. One of the original planners of the invasion, Morgan knew just how critical the weather was to their chance of success.

“Good luck Stagg;” The General told him, aware that tomorrow would be the moment of truth for the meteorologist. “may all your depressions be nice little ones.”

“But remember,” He added cheerfully, after a slight pause, “we’ll string you up from the nearest lamp post if you don’t read the omens right!”

Stagg did not sleep well that night.

June 3 1944, HMS Hoste, West Coast Of Ireland (D-Day -2)

Of all the duties a destroyer could have, Lieutenant Hoare considered weather readings one of the most thankless. Especially, he noted, when taking them required spending a lot of time in an area of sea that German U-boats also seemed to enjoy spending a lot of time in.

At least today U-Boats would not be a problem. Overnight the weather, which had been looking ominous for a while, had finally closed in. As he ordered the latest set of weather readings broadcast back to the Admiralty he wondered absent-mindedly whether they were actually doing anything with these numbers. He hoped so. Otherwise it was a very poor reason for getting a man and his crew so wet.

That same morning, Blacksod Point, Republic of Ireland (D-Day -2)

The phone had been ringing for a while by the time Maureen got to it. When she answered she was surprised to hear the voice on the other end of the phone was English. She asked Maureen to confirm the weather readings that had been sent through in the early hours of that morning.

“I’ll need to get Ted,” she warned the voice, “stay on the line.”

Having located Sweeney she brought him back to the phone where he confirmed both the results and the methods he had used to collect them.

Barely an hour later though, the phone rang again.

“It was the same lady.” Maureen recalled, over 60 years later. “The lady with the English accent and she asked if we could please check and repeat the very latest weather observations we had sent from Blacksod. So Ted repeated those ones again.”

Both Ted and Maureen agreed that whoever this English woman was, she seemed awfully interested in the weather.

That Evening, the Weather Hut, Portsmouth (D-Day -2)

The Admiralty were the first to speak. Although they still didn’t subscribe fully to Dunstable’s bad weather forecast, they did now believe that cloud and winds over Normandy on the day of the landings was more likely than not.

Widewing continued to insist this was not the case. Yes, they admitted, the high pressure they had counted on to protect the beaches was not developing in the way they’d hoped, but they still firmly forecast that Normandy would remain protected from the weather. The invasion could go ahead.

There would be no consensus forecast. Stagg and Yates finished up the call and headed across the grounds to see Eisenhower.

The Moment of Truth

As Stagg waited in the hall for the Supreme Commander’s briefing to begin, he was approached by Air Chief Marshal Arthur Tedder, the man responsible for all air operations during OVERLORD.

“What the devil has been going on behind the scenes in recent days, Stagg?” He asked, “Will you please tell me?”

Tedder explained that he had been up at Bushey Park that morning to meet with General Spaatz, commander of the USAAF in England. Whilst he had been there the two men had decided to call in on Widewing. There, Krick had shown the two airmen their forecasts — forecasts that obviously ran counter to the general image of pessimism that Stagg had been presenting.

“Now tell me Stagg,” Tedder insisted, gently, “just what has been going on around you?”

Stagg’s blood ran cold.

“I’m afraid the weather centers haven’t quite been seeing eye to eye in recent days.” He answered, slowly and carefully. “Widewing’s techniques have led them to be more consistently optimistic than I have thought to be warranted, and I have taken the responsibility of toning down their contributions to the forecasts which I have been bringing you in there. I’m sorry if the Widewing people feel that I have not given their views the consideration they deserve; but I can assure you that nothing would have made me happier than if I could have accepted their forecast of weather for the weekend and Monday.”

Tedder looked at Yates, who was standing next to Stagg. Yates looked at his commander, then at Tedder. This was the moment, Stagg realised. Torn between his boss and his own command, if Yates was going to break ranks it would be now.

Yates looked at Stagg, then at Tedder. Then the American quietly nodded in support of Stagg.

“For everybody’s sake,” Tedder said to the two men, his voice level, “let’s hope it will turn out alright.”

21:30 June 3 1944, Senior Commander’s Briefing, Portsmouth (D-Day -2)

The weather, Stagg explained to Eisenhower and his commanders, had turned against them. The incoming depressions would cause disturbed conditions in the Channel and the assault area throughout the 4th and 5th of June. Winds of up to Force 5 would hit the beaches and surrounding area, and cloud would be low and thick with limited visibility. It would rain both on the British coast and on Normandy.

As he was talking, both Stagg and his audience could not help but keep glancing out of the large bay windows. It was a beautiful, clear, windless night.

All the staff, that is, with the exception of Eisenhower. Throughout the briefing, the General had remained quiet, his chin resting on his hands and his eyes firmly fixed on his meteorologist.

Stagg finished and silence descended.

Air Vice-Marshall Leigh-Mallory, in charge of the invasion’s air forces, broke it. He asked Stagg what the conditions would be for his bombers and fighters.

A 2,000ft layer of cloud would obscure the ground, Stagg told him, somewhere between 1,000 and 5,000ft. Another layer would exist at about 11,000ft.

Admiral Ramsay, the man who had overseen the Dunkirk evacuation on behalf of the Navy and who was now charged with getting the army back into France, asked whether there would be high winds on Monday and Tuesday. Stagg confirmed that this was his forecast.

Eisenhower listened to his staff’s questions and Stagg’s answers, and then turned to Stagg himself.

“Last night you left us, or at least you left me, with a gleam of hope. Isn’t there just a chance that you might be a bit more optimistic again tomorrow?”

“No sir.”

Thanking the forecasters for their input, Eisenhower dismissed Stagg and Yates and asked them to leave the room. As they turned to depart, however, Tedder spoke up.

“Before you go, Stagg,” he said, “will you tell us whether all the forecasting centres are agreed on the forecast you have just given us?”

Stagg paused. He remembered the phone call between Yates and Widewing the previous day. In that moment he realised just how much he owed to his deputy. By securing Widewing’s agreement to back Stagg no matter what, Yates had given him just enough leeway to be able to answer this question honestly.

He turned to Tedder and replied.

“Yes sir. They are.”

With that Stagg and Yates left the room. A few minutes later General Bull joined them and told them that inside they were debating a delay.

Stagg nodded wordlessly and stepped outside. As he did so, Tedder approached.

“He turned to me,” recalled Stagg later, “and, smiling, said, ‘Pleasant dreams Stagg.’”

04:15 June 4 1944, Senior Commander’s Go Briefing, Portsmouth (D-Day -1)

“The sky outside here at the moment,” Admiral Ramsay said, “is practically clear and there is no wind. When do you expect the cloud and wind of your forecast to appear here?”

Stagg had just finished delivering his morning weather briefing. He had told them nothing had changed. Indeed this was true in more ways than the senior staff knew. For the last hour and a half the weather centres had been in discussion and none of their positions had changed either. Dunstable and the Admiralty still said bad weather was imminent over the Channel. Widewing said it would remain clear.

There was one difference now though, although Stagg wasn’t prepared to reveal it yet. Another report had come in just minutes ago from HMS Hoste suggesting that the weather front was moving faster than expected. If that was the case then although the weather might be bad on the 5th June itself, things might clear briefly, and suddenly, straight after. It was too early to tell.

It was decision time now though — go or postpone. Acknowledging their role in the decision, Eisenhower permitted Stagg and Yates to stay in the room for the discussion.

“No part of the air support plan would be practicable.” Leigh-Mallory said. Tedder agreed.

Admiral Ramsay reluctantly concurred. If the forecast was correct, the seas would be too rough.

Of Eisenhower’s lieutenants, only Montgomery disagreed. He pointed out that ships and landing craft had already begun to depart. Various plans and deceptions had been laid around this date. To turn back now would risk chaos, he argued, or German discovery of their intentions. Forget the air operation and the airborne assault, he insisted, they should go.

“Jesus!” Eisenhower shouted at Montgomery, temporarily losing his calm, “You’ve been telling us for the past three or four months that you must have adequate air cover and that the airborne operations are essential to the assault, and now you say you will do without them?!”

The Supreme Commander regained his composure.

“No. We will postpone OVERLORD for twenty-four hours.”

The decision was made.

13:00 June 4 1944, Blacksod Point, Republic of Ireland (D-Day -2 [REVISED])

Ted had brought down another set of weather readings and they’d had a good chat again as he’d dried off by the fire. Maureen was starting to suspect he might be sweet on her. She didn’t mind. She hadn’t told him yet, but she was a bit sweet on him too.

The future Mrs Sweeney picked up the post-office phone and reported the readings. The barometer had now definitely stopped dropping. It seemed a break in the weather might be coming.

20:30 June 4th 1944, Convoy U-2A, The Channel (D-Day -2 [REVISED])

It had taken two destroyers frantically dispatched from Plymouth to catch Convoy U-2A and persuade it to turn round. The invasion vessels it comprised of had already been at sea when the decision to postpone the landings had been made, and they’d missed the signal to return. They’d been halfway to France by the time the destroyers caught up with them.

At first the sailors and men of the convoy had cursed the order. Now though, as night approached and the last stragglers struggled through the growing rain and wind into the shelter of Weymouth Bay, they were far more sanguine about it.

Stagg’s forecast had been right.

21:30 June 4th 1944, Senior Commander’s Briefing, Portsmouth (D-Day -2 [REVISED])

“Gentlemen,” said Stagg, “since I presented the last forecast some rapid and unexpected developments have occurred.”

As the rain and wind whipped against the French doors of the meeting room Stagg proceeded to explain. The reports coming in from HMS Hoste, Blacksod Point and elsewhere suggested that the bad weather was moving through the Channel faster than than expected. There was still more to come, but that was following slowly.

The weather now battering the coast would continue through Sunday and into June 5th as expected, he said. June 6th, however, would be clear. Indeed if their forecast was right, the conditions would be absolutely perfect. Just as critically, so would the day after.

Stagg knew that Eisenhower needed a two-day window. He told the supreme commander that this was it. Although he didn’t mention it this was, for once, something on which all three weather centres agreed.

The senior staff sat in silence for a while. More than a few glanced out the window again, this time looking out on a swirling rain storm. The French doors banged in the wind.

“Admiral Kirk must be told within the next half hour if OVERLORD is to take place on Tuesday.” Ramsay said, referring to the commander of the naval task forces that would need to set out once more.

“If he is told it is on and his forces sail and are then recalled,” Ramsay warned, “then they will not be ready again for Wednesday morning. Therefore a further postponement would be for 48 hours.”

Everyone in the room knew what Ramsay was saying. If they started and stopped again, then they would lose this window of opportunity. They would have to delay until the middle of June at the earliest, or more likely July. The whole invasion would be in jeopardy.

“Looks to me like we’ve gotten a break that we could hardly hope for.” Said General Beddell-Smith, Eisenhower’s Chief of Staff. “It’s a helluva gamble this.”

Eisenhower turned to General Montgomery.

“Do you see any reason for not going on Tuesday?” He asked.

“I would say…” replied Monty, pausing, “…Go.”

“Well boys, there it is.” Eisenhower said, firmly. “I don’t see how we can possibly do anything else.”

Ike watched the rain and the wind raging outside. The weather that, had they proceeded, would right now be wrecking his invasion fleet. Finally he turned to his Chief Meteorologist.

“Well, Stagg, we’re putting it on again.” He said, with a wry smile. “For heaven’s sake, hold the weather to what you’ve told us.”

June 6th 1944. D-Day.

Stagg lay on his bed.

Right now, he realised, 59 convoys, crewed by almost a quarter of a million men, were steaming towards Normandy. In their holds, and on their decks, were 130,000 soldiers and 2,000 tanks. In less than six hours they would arrive at low tide and the attack on the Normandy beaches would begin.

Above his head, he could hear the low drone of thousands of bombers, heading out into the clear dark night to drop bombs and paratroopers on an unexpecting enemy.

The liberation of Europe had begun, and the weather was perfect.

For the first time in two weeks, Group Captain James Stagg closed his eyes and slept like a baby.

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