Clambering through a snowy meadow with drifts up to the tree branches, California’s water managers measured the state’s vital Sierra Nevada snowpack Thursday at a drought-busting and welcome 173 percent of average. Runoff from the overall Sierra snowpack, which provides arid California with a third of its water in a good year, stood at the highest level since 1995 for this point in the year, California’s Department of Water Resources said.