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Vol. 16 No. 10 · 26 May 1994
Diary

The Most Important Weather Forecast in the History of the World

Lawrence Hogben

1853 words

‘Everything on the Normandy beachhead will hang on your weather,’ said the D-Day planners, assuming that we meteorologists had total control of the elements. ‘Just name us five fine, calm days and we’ll go.’ A hundred years of weather records suggested there was no hope of their getting this. They limited their demand to ‘a quiet day with not more than moderate winds and seas and not too much cloud for the airmen, to be followed by three more quiet days.’ On top of this, the military insisted on a late full moon for the parachutists, plus a tide that would be high three hours after pioneer forces had landed at dawn to clear paths through the beach mines and other obstacles. Tides and moon being fully predictable, they would determine possible dates. July would be too late, and May too early. That left just four possible days: 5, 6, 19 or 20 June. We worked out the odds on the weather on any one of these four dates conforming to requirements as being 13 to one against. So meteorologically, D-Day was bound to be a gamble against the odds.

The planners had originally wanted to know how far ahead a correct weather forecast could be made and who should make it. ‘We can make it, one, perhaps two days ahead,’ said the Meteorological Office. ‘We can make it up to five days ahead,’ said the American Air Force. ‘But do they know anything about the sea?’ asked the Royal Navy, who made no promises. To satisfy pride, and to get the best possible forecast, the solution was to form a committee made up of the three groups. However, fear that loud-mouthed Americans might shout down mild British civil servants, or even battle-hardened naval officers, brought about an administrative compromise. The D-Day forecast became a telephonic affair: the six forecasters would stay in three separate centres, joined to one another, and to Eisenhower’s headquarters, by GPO telephones (which worked). A non-forecaster ‘presenter’ would moderate our debates and then explain our agreed forecast to Ike and his staff. Today’s TV weather presenter has a single source of information, but poor James Stagg had three, sometimes hotly divergent views to harmonise. Knowing little about forecasting, he was astounded to discover that, despite all the scientific expertise simultaneously available on his phone, an agreed forecast never emerged easily, even after hours of discussion.

Nevertheless, the three pairs of top forecasters turned out to be a solid mixture, with enough confidence, diffidence, pragmatism, initiative, foresight, hindsight, optimism and pessimism to produce a valid forecast which clearly read ‘go’ or ‘no go’. We all analysed the same hundreds of observations, including decoded German ones, teleprinted to us and plotted on large maps stretching from the Urals to Newfoundland and Greenland. We drew pressure maps for the days ahead, and based our predictions mainly on these – with hunch and experience as our dangerous but necessary allies.

None of us proved to have a monopoly on rightness or wrongness. Our two West Coast Americans from the California Institute of Technology were used to forecasting for Hollywood. Ben Holzman was full of liberal optimism and Irv Krick, a salesman to his fingertips, had total faith in his own five-day forecasts. C.K.M. Douglas, the senior Met Office forecaster, was a good counterbalance, full of wise ‘buts’ and pessimistic ‘ifs’, plus a complete lack of confidence in any forecast that predicted the weather more than about a day in advance. With him, from Norway, where modern synoptic meteorology was born, was Sverre Petterssen. He had emigrated to the Massachusetts Institute of Technology, disliked the West Coasters and argued interminably against them. The Royal Navy provided two sailors who had taken part in earlier Allied landings in North Africa: Geoffrey Wolfe, an urbane Cambridge man from Hove, on the English Channel, who not surprisingly turned out to be quite the most consistent forecaster of the six, and the youngest, myself, a New Zealand Rhodes Scholar and the first ever Naval Instructor to have won a DSC in battle.

Eisenhower and his commanders had about a month to make up their minds about the quality and timing of their weather advice. During the pleasant weather of May 1944, our five-day forecasts proved to be terrible, but our presenter was able to give Ike 18 substantially correct two-day forecasts of suitable invasion weather. So the vital decision on the choice of a D-Day would have to be based on one-and-a-half to two-day forecasts.

Unfortunately, at the beginning of June, forecasting became more difficult when a steady Azores anti-cyclone started to misbehave, and a series of depressions threatened to run across the North Atlantic, with associated fronts menacing a hitherto sheltered Channel. Up to Friday, 2 June, it was still peaceful, but we suspected the calm was near its end. Then began the forecasters’ and the Supreme Commander’s nightmare: a calm period ending – to be replaced when, and by what? We speculated on Friday that the big change might arrive around Tuesday, 6 June. However, by the Saturday morning, our three forecast centres all agreed that the change was upon us, while disagreeing on what it would turn out to be, or when. On Saturday evening the moment for our crunch forecast arrived. The Americans were still relying on the Azores high pressure: they were for ‘go’ on Monday the 5th; the cautious Met Office were for ‘no go’; so were the pragmatic Royal Navy. Ike considered a postponement. Then, during the night, our observations showed that a stormy front was sweeping towards the Channel and, unwillingly, Caltech yielded. At a hairy 4 a.m. meeting on Sunday morning, faced by a unanimous prediction of strong winds, low cloud and rough seas for the Monday, Ike postponed the operation for 24 hours, only two hours before the main body was due to sail. So Monday was out, and the troops in their landing-craft tossed uncomfortably at moorings. The decision had been an emotional drain on all the participants, military and meteorological, and the whole nerve-racking process had now to continue for yet another day.

The telephone debates went on furiously if inconclusively. We all agreed that the key depression whose front had caused the postponement would move north-east and threaten no more. But what would it leave behind? And how quick and how real would the clearance be after the storm? Tricky meteorological questions! On the Sunday evening, in the fine weather which preceded a still-to-happen Monday storm, we had to stop arguing and forecast for Tuesday the 6th. The Americans were again for ‘go’. The Met Office initially hesitated; Sverre said: ‘This is not the invasion weather we envisaged.’ The Royal Navy, this time, opted for ‘go’. So the ‘go’s had it, and it was time to draft a psychologically suitable forecast of wind, wave and cloud, to be passed on to Channel-crossers and their commanders. After hectic interrogation of the presenter, with all the high-ups participating, a provisional decision to ‘go’ on Tuesday was taken by Eisenhower at the 9 p.m. Sunday meeting, although he had no promise of good weather for after D-Day. Our forecast firmed up favourably overnight and at 4 a.m. on Monday, Ike rapidly gave the word. So, irrevocably, Tuesday the 6th it was. Asking one another whether we might be shot at dawn on Wednesday, we forecasters waited to see the actual Monday weather. Our storm, quite a severe one, arrived more or less on time, fully justifying the postponement. Then it cleared from the West, with wind, sea and cloud slowly lessening. This enabled the bombers to bomb overnight, the moon to guide the parachutists, and the 3000 ships, with their seasick thankful for improving seas, to make for the assembly-point in the Channel, and go on to the assault on the beaches.

The gamble that the weather would be both suitable and forecastable had come off. It was the adoption of the untried, apparently cockeyed telephone committee method of forecasting that got the predictions right, aided by the discovery in the course of May that out five-day forecasts were virtually useless. Suppose, for example, that the Americans had been given, as they originally sought, sole responsibility. Their five-day forecast, confirmed by a short-range one, could have fixed D-Day on the stormy Monday the 5th, with disaster to follow. If, similarly, sole responsibility had lain with the Met Office it might not only have said ‘no go’ to the 5th, but also, lacking contra-opinion, to the 6th, thus opening the way to the next possible date, the 19th. The 19th, as it happens, would have been a meteorological disaster. On the 17th, forecasting for it, we unanimously predicted calm, quiet weather – it would have been a ‘go’ forecast. But in the event a persistent, unforecast gale on the 19th destroyed one artificial Mulberry harbour and just spared the Arromanches one – a large army being already, thankfully, ashore. Although my naval colleague and I happened to forecast correctly for the two critical days, our forecasts were as much the fruit of our discussions with the others as of any singular ability. The team forecasts saved us, and the invasion.

Unlike the Allies, German generals had faith in long-range forecasts, to which they had become attuned, perhaps by Hitler’s weather-aided successes in Poland. On Sunday, 4 June, Major Lettau, Rommel’s chief meteorologist, said that there would be no invasion in the next fortnight. ‘The enemy has not made use of three periods of fine weather in May for his invasion and further periods of fine weather in the coming weeks cannot be reckoned on.’ Rommel went home on leave; Admiral Krancke took a trip to Bordeaux; General von Salmuth went hunting in the Ardennes; General Feuchtinger and his chief of staff went on manoeuvres in the Paris night clubs; while on D-Day itself three more serious-minded German generals were conducting a mock invasion exercise at Rennes.

Would today’s weather forecasters do any better now than we did in 1944? They certainly should, with their satellites, computers and weather models. Fifty years ago our only satellites and computers were in our heads and we could find no analogue in our past records for what the Americans afterwards described as ‘a meteorological situation unique in the annals of June weather’.

I am sure that in weather like that of May 1944 today’s experts would improve on us, and make reasonable five-day forecasts. But when one type of weather is changing to something radically different, as it did the following month, I am not so sure. I have been a knowledgeable consumer of Met Office and Météo France one or two-day forecasts for many years and my observation is that the timing and nature of a total change in the weather continue to pose questions which often are not satisfactorily answered. For shorter periods, the accuracy of today’s forecasts is most impressive. In 1944 we only just got the most important weather forecast in history right. But we steered the invading army away from a potential disaster at sea and helped to make ultimate victory feasible.

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Letters

Vol. 16 No. 12 · 23 June 1994

John Bayley refers (LRB, 26 May) to the American ‘occupation’ of Britain in the last war and goes on to deplore the fact that ‘miles and miles of the best East Anglian farmland were devastated to provide a concrete home for the B17s and 24s which, unlike the RAF Lancasters (which none the less carried more bombs), could not be allowed to rest their massive wheels on grass.’ What an awful picture. Poor little England, occupied by Americans presumably as the Channel Islands were by Germans, and buried in American concrete for the benefit of their monstrous bombers, in comparison with the good little green British Lancasters, which nestled in the grass like plover.

Well, I was a Lancaster navigator during the war and I can assure Bayley that these aircraft and the green grass were not the best of friends. On one of the very few occasions on which my Lancaster did touch the grass, the result was nearly fatal. We were coming in to land at Syerston in Nottinghamshire (concrete runways and dispersals). We made an error of judgment and omitted one step in the cockpit drill, with the result that we overran the extent of the concrete, went off the end of the runway and charged towards a steep drop into the Trent. The landing wheels, however, dug into the mud up to the axles and brought the Lancaster to an abrupt stop with not very much weight on the tail wheel.

There were a lot of American runways in East Anglia but there were a lot of British ones too, and the British bomber runways were to be found all the way from Cambridge to Darlington as well.

Noble Frankland
Eynsham, Oxfordshire

There have been a number of accounts of the problems faced by Allied meteorologists in forecasting the weather during the build-up to the invasion of France, and for the actual D-Day landings themselves. It is unfortunate that we do not have the same level of knowledge about events on the other side of the Channel. Lawrence Hogben (LRB, 26 May) reiterates the account given by H.C. Butcher in My Three Years with Eisenhower that the forecasts made by the German meteorologists indicated that the weather would be quite unsuitable for a seaborne assault during early June, and that on 4 June Rommel was advised by Major Lettau, his chief meteorologist, that there could be no invasion during the next fortnight. It is alleged that as a result of this advice he decided to return home for a spell of leave. However, the accounts given by Lettau himself, and by the head of the Zentrale Wetterdienst Gruppe, Werner Schwerdtfeger, suggest that whatever failings there may have been on the German side, they were not meteorological. Indeed, Schwerdtfeger’s own account claims that the Channel coast forecasts for 6 June that were issued by ZWG were, in fact, correct. Unfortunately no relevant official ZWG documents survived the war so it is impossible to settle this point, but an appropriate level of doubt concerning Butcher’s account should be noted.

After the war Schwerdtfeger and Lettau both moved to Madison in the United States, where they became professors at the University of Wisconsin. Professor Schwerdtfeger died in January 1985. My last contact with Professor Lettau was in December of that year, at which time he was still living in Madison.

J.M.C. Burton
Ilkley, West Yorkshire

Vol. 16 No. 13 · 7 July 1994

Heinz Lettau, Rommel’s chief meteorologist (Letters, 23 June), did not move directly to Madison. I admired, and still admire, his meteorological research and I visited him in Cambridge, Massachusetts in 1954. He was at that time a keen player of badminton. He recalled that, after his capture by US forces, he and his fellow prisoners of war habitually drank Aqua Velva aftershave, the only alcohol they could put their hands on. Professor Lettau is still alive and in retirement in Madison.

John Philip
Trinity College, Cambridge

Vol. 16 No. 16 · 18 August 1994

J.M.C. Burton (Letters, 23 June) is quite right to find excuses for the German D-Day meteorologists because Zentralwetterdienstgruppe data for the period, whose existence Burton denies and which I have examined, demonstrate that their short-range forecasts of the weather elements were reasonably accurate. But for operational success, more than this was needed – the implications of a forecast for action purposes had to be clear. German meteorological weaknesses lay not in the forecast but in, among other things, faulty operational interpretation by naval and military executives who lacked suitable criteria on which to base their orders and actions. For example, the German Navy set the outside wind limit for the Allied landing-craft at Force 4, whereas in fact Admiral Ramsay accepted a Force 5 with an occasional 6. This error was important, because the Germans were reading their wind Force 5 forecast for 6 June as meaning ‘invasion not possible’ while we, with a fairly similar forecast, were saying ‘marginally possible’. So we surprised them. If like Eisenhower they had put a couple of real sailors in their forecasting team they might have done better, but being badly briefed, and unmilitary and unnaval, they can, I think, be excused. The main lacunae were naval and military, not meteorological.

Their confident long-range forecasts were, however, less excusable. Before June 1944 the Allies had found that our own five-day efforts were operationally unacceptable. But the German High Command still actually believed such long-range views as Lettau’s, mentioned by Burton, which anticipated no invasion in the weeks ahead. Scientifically unsound and operationally naive, this gave no fewer than five of the High Command an excuse to absent themselves in body and spirit from Normandy. To make such a long-range operational forecast was unwise and to believe it was military folly.

Is the following quotation relevant? ‘When riding en route to the Inauguration ceremonies Jack Kennedy asked Ike about D-Day. To his surprise Ike didn’t credit his success to the epic’s grand design. Instead Ike said the Allies probably prevailed because they had superior meteorologists.’ We meteorologists thought it was because of superior soldiers and sailors, but who are we to query what Ike said?

Lawrence Hogben
Soyans, France

Vol. 16 No. 17 · 8 September 1994

I am intrigued by Lawrence Hogben’s statement that he has examined the forecasts issued by the German Zentralevetterdienstgruppe (ZWG) for the period of the D-Day landings (Letters, 18 August). The late Werner Schwerdtfeger, at that time head of ZWG, has stated quite categorically that no ZWG documentation survived the end of the war. According to Schwerdtfeger, ZWG headquarters moved from Potsdam to Neubiberg in Upper Bavaria during February and March 1945, and later to the vicinity of Berchtesgaden, where it was disbanded. All ZWG records were left under the care of another eminent meteorologist, Hermann Flohn, at Neubiberg, where they were captured by advancing US forces. Flohn was taken prisoner but was unable to persuade the local American commander of the value of the records under his charge. Schwerdtfeger gave a poignant account of how he later found out that these valuable documents were being used as wrapping paper. I would be grateful to Mr Hogben if he could say where the ZWG documents he studied are located since I, and doubtless others, would very much like to see them.

That being said, I feel his account is rather less than fair to the German meteorologists. Schwerdtfeger recorded from a diary note that the forecast issued at noon on 4 June 1944 for 5-6 June ‘specified prevailing winds of Beaufort Force 5, varying between 4 and 6, equivalent to 15-23 knots’. This was similar to advice provided by the Allied forecasters at 0415 on 4 June, which was modified at 1745 that day. The Supreme Commander’s briefing at 2100 indicated winds of Force 3-4 for Monday evening (5 June) along the French coast. In fact, actual winds over the Channel and Normandy beaches were recorded as Westerly Force 4-5 at the start of Monday 5 June, decreasing 3-4 overnight but increasing 4-5 again by the evening of 6 June, D-Day itself.

Schwerdtfeger also gave an account of the forecast he was pressurised into making the following December, prior to the launching of the German counter-offensive in the Ardennes. He was ordered to provide a forecast of five continuous days with weather below operational limits for the Allied air forces. Such a sequence had never been recorded there at that time of year but, and quite unexpectedly to Schwerdtfeger himself, his forecast succeeded in satisfying its unrealistic specification. The result of this admitted fluke was instant promotion.

J.M.C. Burton
Ilkley, West Yorkshire

Vol. 16 No. 14 · 21 July 1994

My letter of 7 July took on faith J.M.C. Burton’s account (Letters, 7 July) of Heinz Lettau as Rommel’s chief meteorologist responsible for D-Day forecasts; but faith has been shaken. My friend Dr Paul Frenzen tells me that, according to Lettau’s son, Heinz’s quite different charge in the spring of 1944 was forecasting low-level winds affecting V-1 bombs aimed at London.

John Philip
Trinity College, Cambridge

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