SONOMA, Calif. — More than 40 percent of California has emerged from a punishing drought that covered the entire state a year ago, federal drought-watchers said Thursday, a stunning transformation caused by an unrelenting series of storms in the north that filled lakes, overflowed rivers, and buried mountains in snow.

The weekly drought report by government and academic water experts showed 42 percent of the state free from drought. This time last year, 97 percent of the state was in drought.

Southern California, also receiving welcome rain from the storms, remains in drought but has experienced a dramatic reduction in the severity. Just 2 percent of the state, a swath between Los Angeles and Santa Barbara, remains in the sharpest category of drought that includes drying wells, reservoirs, and streams and widespread crop losses. Forty-three percent of the state was in that direst category at this time a year ago.

California will remain in a drought emergency until Governor Jerry Brown lifts or eases the declaration he issued in January 2014, while standing in a bare Sierra Nevada meadow that one of the state’s driest stretches on record had robbed of all snow.

State officials said this week that Brown will likely wait until the end of California’s winter snow and rain season to make a decision on revising the drought declaration.

For Northern California, at least, the onslaught of storms that brought the Sierras their heaviest snow in six years and forced voluntary evacuations of thousands of people as rivers surged will likely make it a much clearer call for the governor, water experts said.

Associated Press