Charting mountain snowpack
Editor's note: This story and the images of the SNOTEL sites were originally published in February 2025, when the amount of snow was much higher than this year. These images and video don't reflect February 2026 snowpack conditions, which are at record-lows in the area where Denver Water collects water.
Chances are when you’ve watched your favorite weather person on the local news you may have seen them put up a map of Colorado that shows the statewide snowpack.
If you’re a curious person you may wonder: Why do they show the map? What is snowpack? And where do they get all that information?
We’re here to help answer these questions.
First off, snowpack is the amount of water stored in the snow that blankets the mountains across our state. It’s important to measure the snowpack because the snow is where Colorado gets about 80% of its water supply for household and agricultural uses.
So now to answer the final question: Where does information about the snowpack come from? The data comes from SNOTELs.
OK, so what’s a SNOTEL?
Well, SNOTEL is short for “snow telemetry.” Think of it as just a fancy way of describing an automated weather station in a remote location that beams information back to a database.
“In Colorado, we have 117 SNOTEL sites, and there are over 900 sites across 13 western states,” said Brian Domonkos, a hydrologist with the U.S. Department of Agriculture’s Natural Resources Conservation Service. “These sites have been around since the late 1970s and provide critical information about the amount of water in the snowpack.”
SNOTELs use “snow pillows” to measure the water content.
Snow pillows are rubber bladders on the ground that are filled with water and ethanol (to prevent the water from freezing). The pillow then weighs the snow, like when you stand on a scale to get your weight.
The pressure on the pillow pushes an equal amount of the antifreeze liquid into a measurement tube, which converts the weight of the water contained in the snow into inches of water content. This measurement is the snowpack, which is technically called the Snow Water Equivalent, and also known as SWE.
A sensor reads the SWE from the tube and sends the data to the NRCS’s central database.
“Generally speaking, here in Colorado, 10 inches of snow melted down equals roughly about 1 inch of water,” Domonkos said. “The data is used to predict how much water will flow into rivers and streams when the snow melts in the spring.”
The information from the SNOTELs is used by farmers, ranchers, water utilities, environmental groups and recreationists. Communities also use the information to be aware of the potential for flooding during the spring runoff.
There are 15 SNOTELs in Denver Water’s collection area that are viewed daily by the utility’s water planning team.
“The SNOTEL network is the most important source of information we have to manage our water supply, and I honestly can’t image how we’d get by without them,” said Nathan Elder, Denver Water’s manager of water supply.
Elder’s team uses the data to make informed decisions about reservoir management and whether any water restrictions for Denver Water customers may be needed in addition to the regular summer watering rules.
Denver Water also monitors 115 SNOTEL sites upstream of Lake Powell to keep an eye on conditions in the Upper Colorado River Basin. Denver Water collects half of its water supply from rivers and streams that feed into the Colorado River.
“We use the SNOTEL data to provide insight into potential water rights calls that may impact our operations,” Elder said. “The earlier we have information, the better decisions we can make with our water supply.”
Denver Water also relies on manual snowpack readings collected on snow courses and from data collected in the spring from an Airborne Snow Observatory. Learn about these methods in this TAP story.
Domonkos said the SNOTELs are also critical in monitoring long-term weather trends across the western U.S.
“When you’re watching the news, you’ll see the various river basins showing a certain percent of the normal amount of snowpack for that date,” Domonkos said. “We always like to see the snowpack in the 100% to 120% range so it’s not too high that could lead to flooding and not too low that could lead to water shortages.”
Along with measuring the snowpack, the SNOTEL sites also measure all other forms of precipitation like rain, hail and ice. They also measure air temperature, soil moisture and soil temperature.
“These sites are very important for not only day-to-day weather information, but also for comparing snowpack year to year so we can keep track of any emerging trends,” Domonkos said.
All of the information is available for free on the NRCS website, which has a variety of data from each SNOTEL site. The information can be found on the NRCS website.