Sierra sees best start to the snow pack since 2010

The California snowpack was 109 percent of average for this time of year on Dec. 19, 2019. The California snowpack was 109 percent of average for this time of year on Dec. 19, 2019. Photo: DWR Photo: DWR Image 1 of / 64 Caption Close Sierra sees best start to the snow pack since 2010 1 / 64 Back to Gallery

With nonstop storms barreling across the Sierra Nevada and Cascade ranges since Thanksgiving week, the snowpack is off to a healthy start.

As of yesterday, the snowpack was 109 percent of average for this time of year, and 30 percent of the April 1 average.

The April 1 percentage is considered the most important of the year because it's when the snowpack usually peaks, experiencing more loss than growth. The sun is at its highest point, temperatures are warming, and storm activity subsiding.

"The snowpack is off to a good start," says Chris Orrock, an information officer for the California Department of Water Resources. "If we’re comparing the 19th of December with past years, we haven’t had a larger percentage of snow since 2010. It’s only going to continue to add up with the next couple of storms in December."

Last year, the snowpack was 82 percent of average on Dec. 19, and in 2017 it was 37 percent of normal. The last time the percentage was similar was in 2012 with 94 percent on Dec. 2019. The last time it was higher was in 2010 when the snowpack saw an especially impressive start at 169 percent of normal.

The snow percentage encompasses the amount of snow in the Sierra and Cascades and is calculated using readings from about 130 gauges spread throughout the mountains.

Snow water equivalent is another important measurement. This is the depth of water that theoretically would result if the entire snowpack melted instantaneously. It's a key number used by water managers across the state to estimate anticipated spring runoff.

The snow water equivalent in the Sierra right now is roughly 6.1 inches. A measure higher than this hasn't been taken since Dec. 19, 2015, when the reading was 6.1 inches.

Ski resorts are seeing similar promise with this year's snowfall. In the Tahoe Basin, Squaw Valley-Alpine Meadows has recorded 134 inches since September 1. At this time last year, the ski resort had recorded only 84 inches. "Last year, we didn't hit 134 inches until January 7," says Squaw-Alpine spokesperson Liesl Hepburn.

Hepburn says the most recent years when the resort saw a similar base of snow on the mountain in mid-December was 2012 and of course the banner year of 2010.

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The snow season got off to a slow start in 2019 with October and the first three weeks in November mostly dry. Thanksgiving week, the storm door finally opened and storm activity has been nonstop. A similar scenario unfolded last year and Orrock says this year's percentage is higher mainly because the storms have generally been cold, rather than warmer atmospheric rivers that develop in the waters near Hawaii and deliver more rain than snow.

The Sierra snowpack is one of California's most important water sources, with its spring and summer runoff feeding rivers and reservoirs, watering crops, filling bathtubs and water glasses. Mountain snowpack provides about 30 percent of the yearly fresh water supply for California, according to NASA.

State water managers and farmers are dependent upon knowing the amount of water the snowpack holds. Their plans for the year ahead are based on the results of a snowpack survey conducted around April 1, when snow levels peak.

While this year's numbers show promise, Orrock says it's still too early to make any conclusions about the overall season. If a ridge of high-pressure develops over the state and sticks around for several weeks, as has happened in other years, dry conditions will persist and the snowpack will fall behind.

"We just have to wait and see," he says.

Amy Graff is a digital editor for SFGATE. Email her at agraff@sfgate.com.