The mapping project at NASA's Jet Propulsion Laboratory known as the Airborne Snow Observatory gathers measurements made by specialized instruments aboard a plane. From these measurements, scientists have been able to gain an unprecedented understanding of the amount of water present in the Sierra’s snow. This year, after California’s very wet winter, the totals have been remarkably big.
Using the NASA data, this year's snowpack can be compared with that of 2015, when the state was in the grip of drought. In the above images, the top taken in 2015 and the bottom in 2017, the white areas had a meter, or 3.3 feet, or more of snow on the ground in March. There are some notations on the map that provide a sense of snow depth.
The maps are of the area crossed by the PCT from Smedburg Lake, Benson Pass, and the Matterhorn Canyon in the north portion of Yosemite National Park. These images are part of a larger article in the NY Times this past Sunday (see link below).
https://www.nytimes.com/interactive/2017/03/22/us/california-measuring-snowpack.html?emc=edit_nn_20170326&nl=morning-briefing&nlid=38480872&te=1&_r=0