This week on Blue Dot, we look at how we measure the amount of snowpack in the Sierra Nevada. We hear from Steve Margulis, a hydrology professor at the University of California, Los Angeles, and Michael Durand, a professor at Ohio State University. They both help give us the numbers that tell how much water (we think) is in the Sierra Snowpack, how much meltwater we'll have to use as a state, and how long it will take the snowpack to recover from drought.