Record-Breaking Everest Blizzard Explained | Scientific American

The science behind the record-breaking Everest blizzard that trapped hundreds

By Stéphanie Pappas edited by Jeanna Bryner

A snowstorm that trapped hundreds of hikers on the north slope of Mount Everest last weekend made headlines because of its proximity to the famous peak. But less appreciated was the truly bizarre nature of the blizzard: the amount of snow that fell in 12 hours was 3.5 times greater than anything previously measured on the mountain.

“It’s out of the ordinary in terms of a six-year record that we have Everest weather stations,” says Tom Matthews, a climatologist at King’s College London, who co-led the expedition to the world’s highest weather station, Everest in 2019. He uses a human-size comparison to drive home the strangeness: “In the last six years,” he says, “the tallest person tallest person you saw was someone 6 feet tall who came to base camp; [October] 4, a 23-foot-tall giant coiled up.

About 900 hikers and guides were rescued in the days after the storm, according to the Associated Press. These individuals were hiking to and around the base camp on the northern slope of the mountain in Tibet during the Chinese National Day and Mid-Autumn Festival holidays. In Nepal, precipitation fell as rain, causing widespread flooding and landslides that killed at least 47 people, according to Al Jazeera.

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The severe blizzard dropped about a meter of snow in Tibet’s Gama Valley last Friday and Saturday, according to reports. This occurred during a typically dry and mild period in the region. The monsoon season in Tibet and Nepal lasts from May to mid-September. Most climbers attempt to climb Everest in the spring, before the monsoon begins. The few climbers who attempt to reach the summit in October are attracted by smaller crowds and generally clear skies.

But it was not the mountaineers who were most affected by the storm. The people who were trapped by the snow that fell on October 3 and 4 were tourists trying to view the mountain from its base in Tingri County, Tibet. A popular four to five day trek takes adventurous tourists from Old Tingri village to Everest’s North Base Camp, located at an altitude of approximately 17,000 feet. People can also now drive to North Base Camp, says Kent Moore, a professor of atmospheric physics at the University of Toronto Mississauga who studies mountain meteorology. Last weekend the route may have been busier than usual due to the holiday.

“It’s easy to put yourself in a very dangerous situation right now,” Moore says. Twenty years ago, the event would have been a “Nothingburger,” he adds, because no one in the area would have been there. But improving infrastructure in Tibet has attracted more and more people to the north slope of Everest. And because it’s easy to get to the northern base camp quickly, these tourists may not be as accustomed to high altitudes as hikers heading to the mountain’s southern base camp in Nepal, which requires about two weeks of hiking from Kathmandu.

“A snowstorm at sea level is no big deal,” Moore says. “But when you’re at 5,000 meters [16,440 feet]everything is just harder to do.

According to the Department of Hydrology and Meteorology (DHM) of Nepal, a low pressure system in the Bay of Bengal intensified the monsoon which triggered the rainfall. Hikers also reported near-continuous wind and lightning on Everest’s north slope. Meteorologists are always analyzing weather conditions, Matthews says. But two low pressure systems, one on either side of India, may have contributed to this event by channeling high levels of water vapor from the Bay of Bengal into the Everest region. The fact that the surface of the Bay of Bengal is currently two degrees Celsius warmer than its historical monthly average may have exacerbated the problem, Moore says. Warmer water evaporates more easily, producing more vapor which could then condense into snow.

Heavier precipitation is expected to increase as the climate warms, Moore says. “This is simply because when the air is warmer, it can hold more water vapor,” he adds. “Water vapor is what causes storms and precipitation. »

Since October 6, the monsoon had retreated from the region, according to the Nepalese DHM.

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