LAKE TAHOE (CBS SF) — According to new data released by NASA, the snowpack levels in the Sierra are currently larger than the last four years combined.

The Sierra snowpack is a major source of water for the San Francisco Bay Area and California’s Central Valley. NASA’s Airborne Snow Observatory (ASO) measured the Tuolumne Basin snowpack on April 1.

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The critical annual measurement of snow for states and their inhabitants released on Tuesday revealed the snowpack was at 1.2 million acre-feet (1.5 cubic kilometers). According to NASA, that is enough snow to fill the Rose Bowl in Pasadena nearly 1,600 times.

To put that into perspective, NASA released a model showing the water content of snow in the Tuoloumne River Basin in 2015 and 2017.

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The 2017 California snowpack is close to the largest on the record, NASA said. Those records consists of decades’ worth of snow measurements made at ground level. ASO mapping showed that Tuolumne Basin’s snowpack is twice the volume of last year’s snowpack and 21 times larger than the snowpack of 2015, which was the lowest on record.

The Airborne Snow Observatory is the only program that measures snow depth, snow water equivalent or the water contained in snow, as well as how much sunlight snow reflects over an entire basin. The program using two scientific instruments — a scanning lidar and an imaging spectrometer — on a King Air aircraft.

All other snow-monitoring programs sample only a few locations on the ground or give an average over a broad area, according to NASA.

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