Ever since a series of winter storms began dumping rain and snow in Northern California last year, officials have been looking for tangible signs that all those storms were making a dent in the state’s four-year drought.

This week delivered some pretty powerful evidence. The latest storms over the weekend pushed California’s biggest reservoir past its historical average for mid-March and put the second-largest one at its historical average, officials said. The rising reservoirs, along with growing snowpack in the Sierra Nevada, are important because both are key sources of water for California.