The Man Behind the Snowpack

Eric Larson loves the snow. As much time as he spends in the Montana mountains, and considering his job, he has to.

For more than a decade, Larson has conducted snow surveys for the Montana Natural Resources Conservation Service. With a background in civil engineering and a lifelong admiration for snow and skiing, Larson collects snowpack and hydrology data from measurement stations across the Treasure State. He writes monthly water-supply forecast reports from January to June, providing key data used by farmers and ranchers, recreationists, reservoir managers, and climate scientists, among others.

“Snow is highly important in the western U.S.” said Larson, the water supply specialist and outreach liaison for NRCS, an arm of the U.S. Department of Agriculture. “Particularly in Montana, around 80 percent of our water supply originates from our mountain snowpack.” In this MoJo interview, Larson discusses the importance of snowpack intel and how his team preps all summer for the extensive amount of data they collect. As Greater Yellowstone settles in for winter, close to 100 automated sites across Montana are set to measure another year of precipitation.

Mountain Journal: How did you become interested in hydrology and snow science, and end up in your job in Montana?

Eric Larson: I grew up in Minnesota and always enjoyed water in the summers and skiing in the winters. I was passionate about snow recreationally and realized the importance of it to everything from an early age. I moved to Montana in the early 2000s to go to school … [at Montana State University] for civil engineering and focused on water resources. I was familiar with the snow survey program at the time, using it … mainly for skiing. Professionally, I saw some job openings within the NRCS snow survey program and jumped into my first position in 2013.

MoJo: Why is snowpack data important to collect and what is it used for?

E.L.: In Montana and the western U.S., snowpack is a natural reservoir that builds throughout the winter, and water gradually releases during the spring and summer months. Our biggest consumer of water in the western U.S. is agriculture, so people rely heavily on our data, particularly for irrigation. We also work with water management reservoir operators to determine how much water is anticipated to flow into reservoirs and how much water they should release. 

E.L.: It’s not really within the scope of this program in terms of looking into trends. We just collect all the data and forecast based on current conditions. I have seen some really big [snow] years recently and I’ve seen some really low years. It fluctuates. There are a lot of groups using our data to make some of those forecasts, like the Montana or Greater Yellowstone Climate Assessments, that make predictions on what snowpack may look like mid-century.

MoJo: The Montana Climate Assessment forecasts a reduction in overall snowpack, more frequent drought years, and area precipitation falling more as rain than snow. What are the impacts of those forecasts? Are you concerned?

E.L: It’s concerning to think about a reduction in snowpack because, ultimately, that will be a major change in timing of the water we receive. If we had less snow, that's certainly concerning for the overall water supply during the summer growing season. In these hot, dry summer months, things really start drying up, and if there's no water running into our rivers from melting snow, that's a serious issue. In lower snow years there’s less water for irrigation, recreation, there might be river restrictions for fishing.

If we're receiving more rain rather than snow, particularly in the spring, that water is running through the system faster. Our water supply is mostly stored up in the mountains as snowpack—which melts and releases relatively slowly into our stream systems—but if it was rain, that water goes through the system more immediately. And if you have an above-normal snowpack in June, rain falling on snow melts snow very fast and can cause flooding, as we experienced in 2022.

E.L.: I think that the best path forward in terms of this program is to keep expanding the [SNOTEL] network, providing more data for folks managing that water, and monitoring lower elevation snowpack more as well to see how that’s changing over time. With population growth in the West, it’s going to be even more important to manage that water tightly. And that’s what we do: we provide that information that helps people plan for managing the water.

MoJo: How does your team prepare for the winter data collection?

E.L.: Operating this large network of mountain weather stations requires a lot of fieldwork, planning, logistics and getting out there to make sure they’re all running properly. Currently, eight of us go to all the SNOTEL sites each year and do routine summer maintenance and sensor calibration. In Montana, we have 96 SNOTEL sites, and across the entire Western U.S. network, we have 911 sites. The Montana data collection office also covers sites in northern Wyoming, so we actually have 135 sites that we maintain.

In the summer, we have to go to every single one each year to make sure it’s ready for winter. We swap out the fluid in the precipitation gauge, calibrate the sensors, and make sure to remove any extra vegetation encroaching onto the site.

E.L.: The sites range in elevation across the state. They’re generally located in mid-to-high elevation mountain bands, below alpine. It’s very hard to measure consistent snowpack in alpine areas because of the wind, so we have them in forested areas. The lowest sites in northwest Montana are about 4,200 feet elevation, and the highest sites in the Greater Yellowstone region are about 10,000 feet.

Anytime we’re going to a SNOTEL site, we have to bring all our calibration equipment, which is generally a couple hundred pounds, and tools to fix any equipment that’s broken. Lots of snow and harsh weather can bend equipment. Things can break from wildlife. Bears like to push things over.

So about 40 percent [of the sites] we access by ATV or UTV. We have several sites that are accessed by helicopter, a handful of sites where we can drive a pickup truck to, and then we do have some in wilderness areas on non-motorized trails that require horses to get into the field.

MoJo: How many times were you on a horse for work this summer?

E.L.: I went on a horseback trip to Two Ocean Plateau in Yellowstone National Park this summer. So that was one day riding in 26 miles, one day of work on the site, and the third day riding horses out. That was my only horsepacking trip this summer, but my coworkers went on other ones.

E.L.: Each SNOTEL site has a snow pillow, which measures the weight of the snowpack and gives you the snow-water equivalent. Next to the snow pillow there’s a tower about 20 feet tall, and there’s some hydrometeorological equipment on that tower to measure snow depth and air temperature. We also have a precipitation gauge, which measures both rain and snow. Those are the standard sensors, but we also have some sites with extra sensors like soil moisture, relative humidity and wind speed. And then there’s a shelter for housing all the electronics, which has solar panels on it for powering the equipment, and a transmitter for automated transmitting of the data.

E.L.: The SNOTEL network was originally established in the 1970s ... when technology became available for automatically collecting and transmitting data. One of the oldest sites in the west-wide network is near Bozeman, and that’s the Lick Creek SNOTEL. Prior to that we used snow courses, which are still around.

New sites are still installed today, and a big part of my job is network expansion. I [analyze] where we need new sites, so I go out and try to find these perfect spots at certain elevations, walking around the woods. We typically install one to two new sites per year. In 2020, Congress passed the Snow Water Supply Forecasting Program Authorization Act. We’re currently working on an extra push to install more stations and expand our staff.

E.L.: In the mid-1930s, Congress started realizing the importance of snowpack and water supply. But we didn’t have the technology or electronics for SNOTEL sites so everything had to be manually measured, and they established a program for snow courses, which are still around today. In Montana there are 104 snow courses, and 1,153 in the western U.S.

Snow courses are just a transect of snow sampling points, located in forests and similar spots to SNOTEL sites, out of the wind. We measure the exact same locations across that transect once a month and take the average, [then] get automated daily data from SNOTELS, and monthly data from snow courses. People go out there and measure them with snow tubes, which are basically 30-inch sections, an inch-and-a-half in diameter, lightweight and made of aluminum. You screw the sections together and you take a snow core. Then you weigh that snow core and can calibrate it to inches of water, and they also measure the snow depth.

Our staff isn’t large enough to measure all the snow courses, so we collaborate with different federal and state agencies, contractors and volunteers to get out and take those physical measurements, using skis, snowmobiles or helicopters.

MoJo: What was one memorable experience you had while doing fieldwork?

E.L.: This summer, a coworker and I were working at a SNOTEL site in the Beartooth [Mountains]. I was up on a tower next to the shelter, working about 20 feet in the air. My coworker was on the ground and I heard him yell, “Bear!” Then a grizzly walked over to the site. It was probably about 20 yards away from him. He was right next to the tower, so he just climbed up and joined me on top of the shelter. It was a little scary, but at the same time it was really neat to see that bear. It wasn’t aggressive or anything, just curious. It just walked through and moved on.