The Sierra Nevada snowpack is a classic example of what scientists call “high inter-annual variability.” Translation: whatever’s happening this year, don’t count on it next year — or ever.

Given the whipsaw nature of things, it could reasonably be considered a dicey proposition that California depends on the snowpack for about a third of its water supply. With the climate changing, it’s becoming even dicier. Scientists expect the snowpack to dwindle in coming decades, but within that general decline, higher highs and lower lows are likely.

It can’t get much lower than the winter of 2014-15, the nadir of California’s current drought. On May 1, 2015, water content of the Sierra snowpack stood at 1 percent of the long-term average — virtually nil. Using tree ring evidence, scientists estimated that to be the skimpiest snowpack in 500 years. This spring’s snowpack, while considerably more robust, was still below average. The official stance is that California remains in drought.

Use the interactive tools below to trace the highs and lows of the snowpack over time.

Visualization by Geoff McGhee, David Kroodsma, Erik Hazzard and Mitch Tobin for EcoWest, a collaboration of The Bill Lane Center for the American West at Stanford University and Sea to Snow.