Even after storm, San Francisco faces its third driest period since 1849

An atmospheric river that swept California last week soaked the valleys with much-needed rain and piled up impressive amounts of snow in the mountains, but the Sierra Nevada continues to lag behind the average, and the precipitation was not enough to make up for the San Francisco Bay Area's deficit from last year's dry season and this year's slow start.

The Sierra snowpack is one of California's most important water sources, with its spring and summer runoff feeding reservoirs, watering crops, and filling water glasses. The depth and breadth of it in winter are gauges of the state's future water supply.

At the start of the last week in January, the snowpack stood at 40% of average for that time of year. After the storm that buried the Tahoe Basin in more than 5 feet of snow and dumped nearly 9 feet to the south in Mammoth across multiple days, it jumped up to 70% as of Feb. 3.

"The recent atmospheric river provided a significant amount of precipitation to many areas of the state and contributed to the growth of the seasonal snowpack," said Mike Anderson, California's state climatologist. "Our regional indices and statewide snowpack average from the automated sensor network indicate that conditions have improved from one-third of average to somewhere between half and two-thirds of average."

As an example of the boost to the snowpack, Anderson noted the Central Sierra five-station index, a measure of the snow in the region that includes Yosemite Valley and Mammoth, increased by 6.6 inches to a seasonal total of 12.4...