Mountain events could improve safety with ultra-high resolution weather models

At the end of May 2021, 172 runners embarked on a 100 kilometer (62 mile) ultramarathon in northwest China. At noon, as runners made their way through a rugged, high-altitude portion of the course, temperatures plunged, high winds whipped the slopes, and freezing rain and hail battered runners. By the next day, the death toll from the sudden storm had risen to 21.

A new study looks back at the fatal event with the aim of testing how hyper-local modeling can improve the accuracy of predictions for mountain events. The runners got into trouble as the hourly weather forecast for the race underestimated the storm. The steep mountain slopes had very localized effects on wind, precipitation and temperature on a scale too small for weather predictions of the event, according to the new study published in the journal AGU. JGR atmospheres.

Hourly forecasts for the 2021 race were based on relatively large-scale atmospheric processes, with models operating at three-kilometre resolution – sufficient for most regional forecasts, but too coarse to capture ‘hyper-local’ weather like the storm that hit the price, says Haile Xue, a climatologist at the China Center for Earth System Modeling and Prediction CMA and lead author of the new study. Although a wind and cold weather advisory had been issued the previous night, it lacked the resolution needed to identify danger areas on the course.

“An apparent temperature forecast based on a high-resolution simulation can be useful” in addition to general regional forecasts, Xue said. Conditions like the 2021 storm are common in mountains at extremely high elevations, such as Mount Everest and Denali, the document says. Although less common at lower elevations, when such storms do occur they can strike suddenly and result in injury and loss of life.

The new study uses topographic data from the course, at tens of meters of resolution rather than kilometers, to model the hyper-local weather patterns created by the mountains. With a resolution two orders of magnitude finer than the original forecast for this weekend, as well as detailed considerations of the mountainous topography, the model accurately recreated the storm conditions of the race and even offered better insight. of what might have happened that day.

The initial forecast included a large-scale cold front, which would have brought temperature drops and stronger – but not extreme – winds with only a low-level wind advisory issued. The new study found that the apparent temperature could have dropped as much as -10 degrees Celsius (14 degrees Fahrenheit), about 3 degrees Celsius cooler than the original models predicted.

The model also generated an “impact prediction” including apparent temperature, which could have dropped even lower as it takes humidity into account and would ideally include the effect of wet clothing or skin on temperature. bodily. Including them in forecasts, Xue says, could help mitigate the risk of hypothermia.

Besides the weather, race planning and riders’ equipment needs were discussed after the event. Many endurance events require many layers to protect against heat and rain; these were suggested but not required, which could have contributed to the loss of life. Accurate weather forecasts and equipment requirements are essential for an event to be safe.

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Materials provided by American Geophysical Union. Note: Content may be edited for style and length.