California’s statewide Sierra Nevada snowpack — the source of nearly one-third of the state’s water supply — is at its lowest level in a decade, a major turnaround from last year when huge storms ended a three-year drought and buried ski resorts in massive amounts of snow. On Tuesday, the snowpack was just 25% of its historical average for Jan. 2. A year ago on the same date, it was a staggering 185% of normal. The last time there was less snow at the beginning of a new year was 2014 when it stood at just 19%. The lack of snow so far this year is due to fewer big storms hitting the state than …