A massive storm in the Alps took climbers and skiers by surprise over the weekend and has killed more than a dozen people so far.

The storm followed several weeks of warmer-than-usual weather. The blinding fog and icy winds dropped temperatures to below freezing levels and caught many people on the mountains off guard. In all, the Italian newspaper La Republica reported that 14 people died during the storm, with victims reported in the Italian, French, and Swiss portions of the Alps.

The single-largest tragedy befell a group of 14 mainly European skiers, including an Italian guide, making their way along the Haute Route, a circuitous path that begins in Chamonix below Mont Blanc and ends just below the Matterhorn at about 10,000 feet. The group had set out on a six-day tour. On Sunday, as they approached the Vignettes Hut at the foot of the Pigne d’Arolla peak, the storm engulfed the skiers.

The group’s guide, Mario Castiglioni, went for help but he lost his way in the storm, fell over a cliff, and died. The rest of the group huddled down and had to spend the night outside in the blowing wind. “Hell can only be a night like that and cold like that,” one survivor, an Italian named Tommasi Piccioli told local media. When daylight arrived and the storm passed, the group found that one person had died in the night. They also realized they were only a five-minute ski from the hut. Helicopters flew the survivors to nearby hospitals, where three more passed away. By Tuesday, a total of seven of the skiers were dead, most from hypothermia.

Elsewhere in the Alps, two French skiers died in separate incidents. Two climbers went missing for a day and were later found after a days-long rescue effort. A Russian climber, still missing, has been presumed dead in the Valais Alps, a connected range just to the west. Two Swiss hikers were also found dead. A French hiker died after being taken to the hospital. And two French skiers died in an avalanche at the foot of Mont Blanc.

The Local, a Swiss news website, reported that it’s the deadliest few days in the Alps since 1999, when 12 people died in an avalanche near the Swiss city of Evolène.

At 15,777 feet, Mont Blanc is the highest mountain in the Alps and the tallest in western Europe. It’s also the most deadly. Estimates put the average death toll on the mountain around 100 per year. What makes Mont Blanc so deadly is not its height or technical climbing—it’s the easy access. Guides in the area sometimes advertise trips as if they were day hikes. As writer Lane Wallace pointed out in The Atlantic six years ago after another rash of deaths, gondolas even haul hikers up to 9,000 feet, dropping sometimes inexperienced people in an overwhelming environment. In the spring and summer, Mont Blanc and the surrounding mountains can seem unassumingly attractive to the would-be adventurous—some of whom may be unprepared for a freak storm.