Matthew LaPlante often observes his research firsthand from his home in the mountains near Salt Lake City. After warm nights when temperatures remain above freezing, he notices the snow level receding, exposing more of the aspens he uses for syrup.
“It feels like a monster came and just in the middle of the night, took a bite out of a snowpack,” said LaPlante, a journalist and climate scientist at Utah State University.
Appropriately, scientists have coined the term “snow eaters” for these heat waves, characterized by unusually high temperatures in spring and early summer.
LaPlante contributed to a study published in Science Advances, which was the first to pinpoint conditions that define a “snow eater.” Unlike typical warm spells, these events occur when temperatures remain above freezing day and night for several days, usually three to five. This can accelerate snowmelt, leading to flooding and complicating water resource management.
“Snow eaters” are appearing earlier each year and are becoming more common in the Western United States as the climate changes. Since the 1850s, the area impacted by snow eaters has increased by around 40,000 square miles per century, with the first snow eater of the season arriving a month earlier per century.
The term “snow eater” has a complex history. By the 1880s, people in the West described “snow-eating” chinooks, mountain winds that rapidly melt snow. More recently, the expression “snow-eater heat wave” gained attention in March when an early heat wave swept across the West, quickly melting snowpack in the Colorado Rockies and California’s Sierra Nevada. Scientists hope this descriptive term will highlight these heat waves, as much remains to learn. The study focused on the Western U.S., but these heat waves likely occur elsewhere, LaPlante noted.
According to Noah Molotch, a geography professor at the University of Colorado Boulder not involved in the study, solar radiation is a significant but sometimes overlooked cause of snowmelt. When combined with heat waves, its effects intensify. As snow crystals heat up, they lose some of their structure and reflective properties, causing snowpacks to absorb more sunlight and melt faster. “It’s a little bit of a — no pun intended — a snowball effect,” he said.
This spring, the Western U.S. experienced record-low snowpack. Molotch noted that the anomaly was its wide reach. Colorado had less precipitation than usual, while California saw plenty of precipitation, but mostly as rain rather than snow. However, the common factor across the region was “above-average air temperatures,” Molotch explained.
These conditions likely contributed to severe wildfires in the West, from Utah to Spokane, Washington, where hundreds of homes were lost. “Drought stress for mountain forests around the Western U.S. is heavily dictated by the snow that accumulates each winter and then melts through the spring and summer,” Molotch said. “There is a direct connection there in terms of the water availability and drought stress that can provide one of the important ingredients for increases in wildfire intensity and frequency.”
Improved predictions of snowpack changes could aid water managers in planning for future needs. Early or rapid snowmelt creates challenges for managing water resources in the West, where snowpack is a vital fresh water source during dry summer months. “Water that would otherwise be stored as snow comes out early, and then we have to deal with it as a hazard instead of a resource at our reservoirs and along the rivers and streams,” said Ben Hatchett, a co-author of the study and scientist at Colorado State University’s Cooperative Institute for Research in the Atmosphere.
Snow-eater heat waves may also pose risks to skiers, hikers, and others in mountain areas. They could be linked to hazards such as avalanches, glacial collapses, and permafrost melting, Hatchett noted, although these connections are still under investigation. Living in the Sierra Nevada, he has noticed one clear change over time: the soundscape.
“At night, it used to be quiet,” he said. “And now it’s not quiet, because everything’s melting all the time.”
