In June 2003, Austrian mountaineer Gerlinde Kaltenbrunner found herself stuck at the base camp below Nanga Parbat, the ninth-highest mountain on Earth. She was not alone: A number of world-famous mountaineers, including Ed Viesturs and Jean-Christophe Lafaille, had come to Pakistan to climb the notoriously difficult mountain. But now they were tent-bound due to persistent snowfall. Proceeding from base camp and getting caught in bad weather high on an 8000-meter peak—one of the most remote and savage environments known to humans—is often tantamount to a death sentence, so the climbers were forced to wait for better conditions.
Fortunately, Kaltenbrunner had, for the first time, brought a satellite phone with her. She phoned Karl Gabl, an Austrian meteorologist recommended by her then partner, fellow climber Ralf Dujmovits. “I had never met Karl in person, but he agreed to let me call him during the expedition,” recalls Kaltenbrunner. Gabl told her that the following Friday would be a good day to climb to the summit, with light winds and clear skies. This meant she would have to climb for a few days in bad weather on the lower parts of the mountain to take advantage of the short “weather window” for the summit day.
After the call, Kaltenbrunner exchanged information with the other climbers, who had accessed multiple weather reports from the US and France. “At that time, Karl was just as unknown as I was, and I was almost laughed at for planning the summit on Friday,” says Kaltenbrunner. “The weather reports of the others did not predict passable summit weather for that date.”
Spanish climber Iñaki Ochoa de Olza was the only one who decided to join her. As planned, they started in bad weather, only to reach the summit amid perfect conditions on Friday, exactly as the Austrian meteorologist had predicted. “Back at the base camp I was asked whether I could pass Gabl’s telephone number,” says Kaltenbrunner, who in 2011 became the first woman to climb all 14 of Earth’s 8000-meter-plus mountains without the help of high-altitude porters and supplementary oxygen.
During the last 30 years Gabl, the former head of the Innsbruck meteorological office and a mountain guide himself, has helped hundreds of mountaineers assess the weather during their high-altitude expeditions and plan their attempts to summit. He has continued providing forecasts even though he retired a decade ago, and he has never collected a cent for this additional work. “I see them as my friends, even children,” says the 75-year-old meteorologist, who often goes by the name Charly. “And you don’t charge your family.”
Such is Gabl’s reputation in the mountaineering world that Italian alpinist Simone Moro, the only person to climb four 8000-meter peaks in the winter, almost religiously believes in his predictions, readily abandoning ambitious expeditions in bad weather if the Austrian meteorologist cannot foresee any improvement in conditions. “Karl Gabl is never wrong,” Moro has commented on more than a few occasions.
When the weather is personal
Growing up surrounded by mountains in the Austrian ski resort village of St Anton am Arlberg, Gabl was immersed in nature from an early age. He comes from a family of mountain lovers: His uncle Franz Gabl won an Olympic silver medal in downhill skiing in 1948, and his cousin Gertrud Gabl was the first overall winner of the skiing World Cup in 1969.
Gabl received his PhD in meteorology from the University of Innsbruck in 1976 and went to work at Vienna’s Central Institute for Meteorology and Geodynamics. In 1978 he became head of the Innsbruck regional meteorological office.
Although Gabl remembers being intrigued by weather-driven catastrophes even as a child, it was the tragic death of Gertrud in an avalanche in 1976 that prompted him to act to help prevent mountain accidents. He was a mountaineer himself; by the end of the 1970s he had been part of teams that accomplished the first ski descent from the top of 7492-meter Noshaq in Afghanistan and the first ascent of the south spur of 6768-meter Huascarán in Peru. As such, he was painfully aware of how neglected the mountain environment was in weather forecasting.
“A friend of mine and his wife died on Mont Blanc [in the Alps] due to a sudden weather change,” recalls Gabl. “I calculated later that they had started from the Aosta Valley in Italy in perfect weather, but a massive cold front was moving over the Atlantic Ocean, and one day later they got hit by a storm with winds up to 130 kilometers per hour and temperatures of –20 °C,” says Gabl. Unable to move in those conditions, they died together on the top of the mountain.
At that time in the Alps region, France was the only country that provided specialized weather forecasts for the mountains. It was also impossible in the Alpine countries to get a weather forecast by phone in more than one language. Collaborating with the German and Swiss national weather organizations, Gabl helped establish a phone service for mountaineers to get weather reports in three languages. In 1987 he started issuing an Alpine weather bulletin for the Austrian and German national Alpine associations. Subsequently he began teaching basic weather courses to mountain guides and helping climbers on high-altitude expeditions.
A major improvement in meteorology, says Gabl, came with the availability of more precise global numerical prediction models in the 1990s. The new resource came in handy for his first forecasts for the Himalayas, which he made for Dujmovits in 1995.
Keys to the forecast
Even today, with the ubiquity of sophisticated computer atmospheric models, predicting the weather on Earth’s tallest mountain ranges is never simple. Mountains force approaching air masses to rise, resulting in the cooling of the air and more precipitation, especially on the windward side. Generally, the higher the mountain, the heavier the snowfall, although local terrain differences also heavily influence precipitation amounts.
Home to 10 eight-thousanders, including Mount Everest, the Himalayas are prone to seasonal weather changes influenced by the subtropical jet stream (STJ), a belt of high-speed westerly winds in the upper atmosphere that blow atop regions of subtropical high pressure. The STJ “is an extremely important driver of winter weather over the Himalayas, in much the same way as the North Atlantic jet stream is for western Europe,” says Kieran Hunt, a senior research scientist in tropical and Himalayan meteorology at the University of Reading, UK. “Cyclonic storms travel along this jet, intensifying until they reach the Himalayas, where they effectively take moisture from the Arabian Sea and dump it as heavy snowfall over the mountains.” The STJ usually stays over the Himalayas from late autumn to early spring. Its movement much farther north in the summer marks the beginning of the rainy monsoon season.
Climbers in the Himalayas in Nepal and Tibet usually choose to ascend in the spring and the autumn months, with milder winds and less precipitation. In the neighboring Karakoram range in Pakistan, home of K2 and three other eight-thousanders, summer is the main season to climb because the monsoon doesn’t reach those slopes. Still, some mountaineers go to the Himalayas and Karakoram in winter, intentionally seeking a bigger challenge. For them, the problem is not only heavy snowfall and temperatures as low as –50 °C but also hurricane-strength winds that the STJ regularly brings. Even at base-camp altitudes of about 5000 meters, the climbers often must cope with wind speeds up to 130 kilometers per hour.
When producing forecasts in winter, Gabl says, it is very important to know where the STJ is positioned. For example, if the jet shifts slightly north, explains Hunt, it increases the distance between disturbances from the west and their moisture source (the Arabian Sea), so they precipitate less. Even knowing the STJ position, there are so many other variables that huge discrepancies frequently arise among different model predictions. It’s not uncommon, says Gabl, that one model shows 40 centimeters of fresh snow and another predicts zero.
As a result, Gabl usually starts looking at models a few weeks before an expedition, learning how well they match actual conditions. “For example, I find the American GFS [Global Forecast System] model more accurate when it comes to information about convective cells, but the ECMWF [European Centre for Medium-Range Weather Forecasts] model is much better in terms of moving fronts and their development,” says Gabl. Due to the Himalayan heights, Gabl also relies on high-level weather charts used for aviation, which show wind, temperature, and humidity patterns at higher altitudes.
To verify the situation, he regularly checks the data from radiosondes deployed in India and China. The small devices, equipped with sensors and carried aloft by weather balloons, transmit pressure, temperature, relative humidity, and GPS position every second. “You can see the current meteorological conditions from the bottom to 9000 meters and compare it to the model,” says Gabl.
An “additional member of the expedition”
Although his meteorology credentials are impeccable, Gabl attributes a large part of his popularity among hardcore climbers to his mountaineering knowledge. After all, he has climbed a few dozen peaks above 5000 meters. He has visited the Himalayas 20 times and has spent days fighting cold and wind while trying to climb two eight-thousanders. He knows which questions to ask climbers about current conditions or how long will it take them to get from one camp to another. Most important, he knows how many hours of a weather window are needed for a summiting attempt. “I’m like the additional member of the expedition,” Gabl says. “I know what it means to make decisions in the mountains.”
The climbers he has advised praise Gabl for never forcing them into a decision. “He always leaves the final decision to me,” says Dujmovits. Even so, the combination of the complexity of the forecasts and the potentially life-and-death consequences has kept Gabl awake on many nights. And there have been harrowing episodes. The one that first comes to his mind occurred in 2011 when Moro and his two partners made the first winter ascent of 8035-meter Gasherbrum II in Pakistan. For the later stages of their ascent, Gabl had predicted 36 hours of good weather—just long enough for the team to reach the summit and descend quickly before heavy snowfall arrived.
At first everything went according to plan. “They started climbing during the storm, and the next day they managed to summit before noon,” recalls Gabl. But on the descent, the climbers faced heavy fog and had a hard time finding a feasible route. They had to stay one day longer on the mountain, as back home Gabl anxiously waited for news of their safe return. The weather window closed, and the climbers were caught in an avalanche just before reaching base camp. With luck and skill, they managed to survive.
“Charly’s forecasts are always part of decisions I make in the mountains,” says German alpinist Thomas Huber, who is known for his difficult first ascents in many parts of the world. He estimates that his chances of success would be halved without them.
In general, the era of more precise forecasts has changed mountaineering, improved outcomes, and saved lives, Huber says. In 2007, on notorious K2, the second-highest mountain in the world, Huber and his partners didn’t hesitate to turn around even though they were close to the summit. They knew they wouldn’t have had time to reach safety before 7:00pm, when Gabl predicted that stronger wind would arrive. “Charly is one of the best,” says Huber. “He loves the mountains and feels the passion of his clients. He is the first one that we call when we come down.”
Despite his age, Gabl not only continues to make weather forecasts but also still goes skiing and hiking. Four years ago, he almost died in a car accident during a trip to Bolivia’s mountains, suffering internal bleeding and sustaining 20 broken bones. He was attached to a mechanical ventilator for 10 days.
A year later he climbed Russia’s Mount Elbrus, the tallest European peak.