Typically, weather systems are on the move. A convective storm comes and goes within a matter of hours, a blizzard might last a day or so, or a cold front could extend a few days. Sustained, intense weather events lasting several days often result in more significant damage to communities and the natural and built environment than shorter events.
Research Scientist Alan Rhoades led a collaboration that identified a new category of heat waves, called “snow-eater” heat waves — defined by an abnormally sustained, persistent high-pressure system lasting three or more consecutive days and capable of causing snowpack to melt twice as fast as expected. A paper recently published in Science Advances defines these types of heat waves that, by influencing rapid snowmelt, can ultimately undermine water supply reliability, increase flood risk, and contribute to drought stress.
In this Q&A article, Rhoades discusses the science behind these heat waves and the importance of studying them as they become more widespread across the Western United States and beyond.
How do snow-eater heatwaves form?
Snow-eater heat waves are caused by the buildup of an abnormal, persistent high-pressure system that diverts storms, acting like a boulder diverting water in a stream. This buildup of high pressure leads to warmer and drier conditions that can sustain above-freezing conditions throughout the day and night. When these conditions persist for several days, snowpack melts twice as fast as is typically expected during the spring and early summer.
What makes snow-eater heat waves distinct from other types of snow melt events?
When typical warm spells occur, their temperatures are highest during the day, but then drop to lower temperatures that allow snow to refreeze at night, which helps reduce snowmelt. Snow-eater heat wave temperatures, however, are consistently above freezing throughout the day and night. This means that the persistent high-pressure system continuously melts snow for over three days, as opposed to other, shorter melting events that reduce snowmelt with nighttime cooling.
Are there any examples of recent snow-eater heat waves?
Snow-eater heat waves have occurred often over the last few centuries, but a particularly impactful one just occurred in March of 2026. This event compounded an already bad situation throughout much of the mountainous Western United States, where drought conditions–particularly snow drought–persisted for most of the winter. After the snow-eater heat wave occurred, the already-meager amount of mountain snowpack rapidly depleted.
This resulted in the 2nd lowest inflows on record to Lake Powell, our nation’s largest reservoir, at a time when Colorado River water managers were hoping for a “miracle March” to alleviate stress on the Colorado River. However, by the end of the water year 2026 (October 1, 2025 through September 30, 2026), water levels in Lake Mead and Lake Powell had fallen to historic lows.
How can your research help better predict snow-eater heat waves?
To better forecast snow-eater heat waves and their magnified impacts on snowmelt behavior, we used a snowmelt model developed by the U.S. Army Corps of Engineers and the National Weather Service, and combined it with a dataset that provides global weather estimates back to the 1800s. We then optimized this model to infer potential changes in snowpack measured at longstanding SNOw TELemetry sites throughout the mountainous Western United States.
The model showed that over time, snow-eater heat waves have increased in area and frequency, decreased in duration, and shifted to occur earlier in the melt season. Since this is a new heat wave classification, documenting these types of patterns can inform planners of what to expect and how best to prepare for when they occur, in addition to any actions that could help mitigate their effects.
Why are these heat waves important to research?
These events can occur during a time of year in which water resource managers have already started to quantify, plan, and budget water resources. When snow-eater heat waves occur, they can significantly reduce how much water is available for communities, agriculture, industry, and more, when they need it most. This water loss occurs through rapid depletion of existing snow, to the atmosphere or to recharge parched soils and groundwater, or through abrupt and punctuated rather than gradual and sustained snowmelt. Identifying, monitoring, and forecasting snow-eater heat waves can allow us to better account for their effect on water resources to mitigate potential consequences and improve water allocation plans.
But the effects go beyond water supply. Our study found that seven of the past 11 superfloods in the Western United States coincided with a snow-eater heat wave, suggesting they could increase the risk of severe flooding. And this type of rapid, widespread snow loss creates drought conditions. We also posit that they could be tied to avalanches, glacial collapse, and permafrost thaw in other mountainous regions, but more research is needed. Studying snow-eater heatwaves can help us better understand and plan for their compounding consequences.
Can you apply this model to predicting snow-eater heat waves in other mountain regions?
Other mountainous regions, such as the European Alps, could potentially benefit from the modeling framework we have put together. The Alps have experienced several periods of abnormally warm, sustained, and above-freezing conditions in the spring season that rapidly melted snowpack covering their iconic glaciers or even the glaciers themselves. Additionally, during these periods, the ice in permafrost layers locked in mountain faces has melted, allowing the rocks that were once “glued” together to become more mobile, resulting in dramatic rockfall and mass movements. We think these events could be linked to snow-eater heat waves, but we have yet to explore this.
