There’s still snow in Colorado’s mountains near the headwaters of the South Platte River, and Brian Domonkos has strapped on a pair of cross-country skis to come measure it.

He’s the Colorado Snow Survey supervisor, and knowing how much snowpack is left from the winter to runoff into streams, rivers and reservoirs this summer is crucial, especially in a year when much of the West is in extreme drought. As it melts, the snowpack here will become the primary source of water for millions of people in Colorado and across the West.