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.