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A new modeling tool from INSTAAR provides weekly snow-water equivalent estimates for the entire Western US.��

Last week, INSTAAR’s��Mountain Hydrology Group ������𲹲������its fifth near-real-time report on snow-water equivalent (SWE) in the Western US in 2025. In essence, the report provides a snapshot of how much water is stored in snow on the landscape—water that will feed our rivers and streams in the months to come.����

The end-of-March report is of particular interest for water managers in the West, because it arrives around the time that snow in the region reaches its peak. Last week’s report will help managers adjust plans for the spring, summer and fall.��

“It helps inform how much water storage they might have and when that might come down into their reservoirs,” INSTAAR PhD student and report co-author��Emma Tyrrell said.

Other tools for visualizing the snowpack exist, such as, which plots various SWE-measuring stations. But, the Mountain Hydrology Group’s reports take a uniquely comprehensive approach. The team combines multiple data sources and modeling tools to estimate the amount of water stored in snow across the entire landscape.��

The skinny

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A map showing the percent of the long-term (2001 to 2021) average snow-water equivalent in major regions of the Western United States as of March 31, 2025.��

Here in the Front Range, the report shows SWE totals lagging behind the 2001 to 2021 average. However, the overall trend doesn’t hold at all elevations. While the plains and foothills have less snow than average, many mountainous areas, like the headwaters of the ����ֱ�� River, sport average or higher-than-average snowpacks.��

“Where you might go skiing, we’re seeing around 100% of normal,” Tyrrell said.��

If you zoom out to the entire Western US, the report shows some anecdotal regional trends. The Desert Southwest has had a dry winter, with many regions dipping below 50% of average SWE and some in the single digits. On the other hand, a pocket of mountainous regions in the Northwest, stretching from Western Wyoming to Oregon, is experiencing an unusually robust spring snowpack.

“We’re seeing a somewhat typical north to south gradient during a La Niña cycle,” ��senior professional research associate Leanne Lestak told INSTAAR.

An experiment, a product

The Mountain Hydrology Group, led by INSTAAR faculty fellow Noah Molotch, has been producing SWE reports for the Sierra Nevada Mountain region in California since 2012. There, water managers and river forecasters have come to rely on the reports.

“We work really closely with the California Department of Water Resources." Lestak said. “The hydrologic engineers use our data in their forecasts, and they really rely on what our reports have to say. It’s such an honor to work with these folks.”

The west-wide report is a newer endeavor—the group put out the first of its biweekly reports this February. Like the Sierra Nevada reports, the west-wide reports draw on a mix of satellite imagery, remote snow sensors and statistical modeling to arrive at its estimates. When they can, the team also calibrates their results by comparing them to “Airborne Snow Observatories,”—intermittent snow surveys conducted via manned aircraft�� and��.

“We consider them a ground truth,” Tyrrell said. “It’s a patchwork of data that we can use to bias correct.”

While the methodology that the ����ֱ�� team uses for the Sierra Nevada reports has been refined by years of tweaking, the west-wide methodology is still new—it’s an experimental product. It will take a few years for the team to refine the model and build trust with stakeholders.

Locally, the project has already garnered some interest.

“Denver Water and other local cities are interested,” Lestak said. “There aren’t a lot of products here on the Front Range.”

We may have reached peak SWE for 2025 here in the west, but the Mountain Hydrology Group will keep issuing reports until mid summer. All the while, they will work to refine their tools.��

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If you have questions about this story, or would like to reach out to INSTAAR for further comment, you can contact INSTAAR Communications Specialist Gabe Allen at gabriel.allen@colorado.edu.