‘Snow Eater’ Heatwaves Are Arriving in Western US

Rocky Mountain National Park. Photo by James Coffman on Unsplash.

“Snow Eaters” are a new type of heatwave that’s becoming more widespread across the western United States.  It presents unusually warm conditions rapidly melting mountain snowpack earlier in the year. Scientists called it so, because temperatures remain above freezing both day and night for several days, accelerating snow loss. These events can roughly double the rate of snowmelt, as found by a new study published in Science Advances. Moreover, this increases the risk of flooding while reducing the amount of snow available as a natural water store for the drier months. 

The problem is becoming more widespread and occurring earlier in the year as the climate warms. Since the 1850s, the area affected by snow eater heatwaves has expanded by about 40,000 square miles per century, while the first snow eater of the season is arriving about one month earlier per century. Rapid snow loss can put pressure on water supplies, increase drought stress in mountain forests and contribute to conditions that fuel more severe wildfires across the West. 

What is Happening? 

• A new heatwave category, the “Snow Eaters”, is emerging: they occur when temperatures remain above freezing during both day and night for roughly three to five days, causing snowpack to melt rapidly. 
• Snow is disappearing faster: These events can roughly double snowmelt rates, turning snow that would normally be stored for later into early runoff. 
• Snow eaters are becoming more widespread: Since the 1850s, the area affected has increased by an average of about 40,000 square miles per century. 
• The season is starting earlier: The first snow eater is now arriving about one month earlier per century, giving snowpack less time to remain stored in the mountains. 
• Water supplies are at risk: Mountain snowpack acts as a natural reservoir, releasing water gradually through spring and summer. Earlier melting means more water arrives when it may be harder to store and less remains for the dry season. 
• Wildfire risk can increase: Reduced snowpack can leave mountain forests drier for longer, increasing drought stress and contributing to conditions that can intensify wildfires. 

Why This is Getting Worse 

The “Snow Eater” heatwaves are becoming more likely as the climate warms. Warmer temperatures mean more winter precipitation falls as rain rather than snow, while existing snow melts earlier thanit’s supposed to. Research across the western US has documented declining snowpack and earlier snowmelt, reducing the amount of water naturally stored in the mountains for summer. 

This is also part of a changing polar climate. The Arctic is warming nearly four times faster than the global average, a phenomenon known as Arctic amplification. Research suggests that rapid Arctic warming and sea-ice loss can influence atmospheric circulation, including the jet stream, potentially affecting weather patterns across the Northern Hemisphere. 

The implications are significant because mountain snow provides water for around 1 billion people globally.  

At 42% of snow monitoring stations, the share of annual snowmelt occurring before April increased by about 3.5% per decade, meaning more water is being released earlier rather than stored for the warmer, drier months. Combined with increasingly rapid “snow-eater” heatwaves, this could put greater pressure on summer water supplies, agriculture, ecosystems and wildfire preparedness. 

What This Means for People

• Water security: Earlier snowmelt can reduce water availability during the dry summer months, affecting households, agriculture and ecosystems. 
• Flooding: Rapid snowmelt can increase runoff and contribute to flooding in rivers and streams. 
• Wildfires: Less snow stored in the mountains can increase drought stress in forests and contribute to more intense wildfire conditions. 
• Agriculture: Farmers and communities that depend on mountain snowmelt for summer water supplies may face greater uncertainty over water availability. 
• Outdoor recreation: Rapid snow loss can shorten ski seasons and increase risks for people in mountain environments. 
• Mountain hazards: Rapid melting may contribute to hazards including avalanches, glacial collapse and permafrost thaw. 

The Urgent Response Needed 

What needs to change: 

• Improve snowpack monitoring and forecasting so communities can better prepare for earlier and faster snowmelt. 
• Strengthen water storage and management to capture more runoff when snow melts earlier than expected. 
• Prepare communities for flood and wildfire risks linked to rapid snowmelt and increasing drought stress. 
• Improve climate-resilient water planning for agriculture, cities and ecosystems that depend on mountain snow (e.g., irrigation water, drinking-water reservoirs). 
• Plan for earlier snowmelt: Cities, farmers and water agencies should account for earlier snowmelt when planning seasonal water supplies. 

What YOU Can Do:

• Use water efficiently, especially during dry summer periods and local water shortages. 
• Support water-resilience measures such as improved storage, conservation, efficient irrigation and watershed protection. 
• Stay informed about local flood, wildfire and water-supply warnings, if living near mountain watersheds. 

Read more: Extreme weather events | Health risks | Climate Risks Daily 

Original source: https://www.science.org/doi/10.1126/sciadv.aeb3361