Sometimes you need a weather forecast to save the washing. Sometimes you need one to save the world.
Eighty years ago, the Allied armies first landed on the beaches of Normandy, France, to begin liberating the occupied countries of Western Europe from Nazi Germany’s rule. A team of six weather forecasters was assembled to provide the Allied commanders with the best information for the D-Day landings on June 6, 1944. They had none of the technology of today – satellite imagery, computer modelling – just weather observations and an innate feeling and experience of how the weather would develop.
Leading them was Group Captain James Stagg, a by-all-accounts dour Royal Air Force officer. Among the six was a Kiwi: Royal Navy meteorologist Lawrence Hogben, an Aucklander who was on a Rhodes scholarship to Oxford when World War II broke out.
It’s fair to say the future of the Western world that June day hinged on the accuracy of the weather forecasts. Has there ever been a more important forecast, such a desperate need to get it right?
For many of us, checking the weather forecast in the morning is like eating breakfast or cleaning our teeth – rarely a matter of life or death, though it provides important information on which to base our day. But with climate change injecting extra energy into the atmosphere, the weather is getting increasingly severe: accurate forecasting is crucial to ensuring we are prepared for the worst. At such times, forecasters walk a tightrope between getting their warnings correct or appearing to be crying wolf.
In 1944, the forecasters brought together for Operation Overlord – the secret codename for the Battle of Normandy – were faced with the mother of all tightropes. The landing in France was scheduled for an early morning during the first week of June. All forecasters had to do was pick when the most suitable weather also fitted in with a full moon, low tides and the right sea conditions for a fleet to cross the English Channel.
Led by Stagg, the forecasters – two each from the Royal Navy, US Air Force and UK Met Office – worked in pairs, communicating and defending their findings by phone.
“A non-forecaster ‘presenter’ would moderate our debates and then explain our agreed forecast to Ike [Allied Forces Supreme Commander General Dwight Eisenhower] and his staff,” Hogben wrote many decades later. (Awarded a US Bronze Star for his role in the D-Day meteorological team, he stayed in Europe after the war, and died in France in 2015, aged 98.)
“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.”
Despite it being early summer, the weather was throwing all sorts of spanners at the forecasters. Frequent low pressure systems and cold fronts crossing the UK and Western Europe were bringing very unsettled and changeable weather. That meant the window of opportunity for the landing – when conditions improved enough between systems for a 12- to 18-hour period – was very narrow.
However, the Allies had a massive advantage. Thanks to the cracking of the German enigma codes by Bletchley Park cryptographers – ironically by recognising the pattern formed by the number codes used for transmitting weather observations – the Allied forecasters were able to draw much more accurate weather charts than the Germans could. From those, they could estimate lulls in the wind and potential invasion periods.
Based on this information and an approaching spell of quieter weather, Stagg, Hogben and colleagues advised the invasion commanders to delay the landings from the 5th to the 6th, to allow a cold front and low pressure system to move away. Stagg said even the 6th was marginal, but the invasion was on. The rest is history.
At the UK Met Office’s Exeter headquarters, the weather chart for 1pm on D-Day hangs framed in the foyer. Alongside is a memo from Stagg on which Eisenhower has scribbled: “Thanks – I thank the Gods of war we went when we did!”
Met Office archivist Catherine Ross says the chart on the wall serves as a reminder of “the most important forecast the Met Office has ever produced. The lives of over 150,000 Allied soldiers, sailors and airmen and the success of Operation Overlord depended on its accuracy. It represents our pride in our 170-year history.”
Heavy responsibility
New Zealand forecasters have never had to give advice on something as world-shaping as D-Day. However, their expertise is called on regularly for search-and-rescue missions, military manoeuvres, aviation and maritime operations, firefighting, protecting roads and electricity networks, and for weather-dependent work.
A precise forecast is essential for farmers, builders, pilots, those on the high seas and others whose work and wellbeing depend on the weather to ensure they, and those they transport, are safe and their business is profitable.
When the weather is settled, it’s easy to make fun of forecasts or treat them lightly. It’s when the weather is at its most dangerous that forecasts have to be spot-on. The responsibility weighs heavily on the shoulders of forecasters, who are well aware of the importance of getting it right.
Ask government agency MetService or private entity WeatherWatch what they consider their most important forecast in recent decades and the answer for both is February 2023′s Cyclone Gabrielle.
WeatherWatch head weather analyst Philip Duncan says the deadly ex-tropical cyclone was the most vital, and the most stressful, prediction he has had to nail in 15 years in the business.
“Gabrielle was so big and so serious-looking when it was already into the New Zealand area. Most of the modelling we look at usually sees them falling apart at Northland and we’re trying to work out, will they go further down the country? But we knew this was absolutely going to do that.
“Not only that, it was coming into the most populated part of the country, Auckland. When you see two million people in the firing line of one of the biggest storms we’ve seen in a generation or two, that’s a little overwhelming.
“I remember the video that I recorded on the Saturday, three days before it arrived, and I threw up before I recorded it. My brain was going, ‘This is going to kill people.’ That’s the worst thought that you can have as a forecaster.”
Eleven people lost their lives.
Duncan says the consistency of the computer models more than a week out in picking Gabrielle would hit New Zealand made it even more stressful.
“Seeing MetService put out an alert about a cyclone about a week in advance was something I’d never seen them do before.”
MetService meteorologist John Law says the clarity from the models had given forecasters more confidence to make early warnings.
“Thankfully, it’s a very rare occurrence to have fatalities from weather in New Zealand, and the reason we do the forecast is so we can minimise that kind of loss, so it’s at the forefront of our minds.
“As soon as we have situations like we had with Gabrielle, the communication and co-ordination of the message becomes much bigger, because it has the potential to affect many more people, and those impacts can be quite drastic.
“You’re really keen on making sure that the forecast goes out, that you’re giving people the information they need, but that you’re not unnecessarily scaring or spooking people, because you want to make sure that the terms you’re using for this once-in-a-lifetime event are heard.
“You don’t want to get into the situation where every warning is the same so every warning is ignored – you don’t want to build that warning fatigue.”