The biggest blizzards are over. But as state water officials head into the Sierra Nevada on Thursday for the annual April 1 snowpack reading — the most important of the year for planning summer water supplies — California still has a huge amount of snow covering its highest mountain peaks, an avalanche that has buried the state’s punishing drought. On Tuesday, the statewide Sierra snowpack stood at 164 percent of its historic average, a massive accumulation of new water. It’s the largest snowpack since 2011, when it was 171 percent of normal on April 1.