There’s still a month left, but this winter in California so far can be summed up in two words: Roller coaster.
It began so dry that Lake Tahoe ski resorts couldn’t open for their usual Thanksgiving kickoff. Then 10 feet of snow fell around Christmas, saving ski season and bringing totals up to historic averages. But five weeks of warm, dry weather followed. Then in mid-February blizzards dumped another 9 feet in five days, contributing to deadly avalanche conditions.
On Thursday, the statewide Sierra snowpack — which provides nearly one-third of California’s water supply — stood Thursday at 68% of its historical average and falling, with at least more two weeks of dry weather forecast.
“It’s a weather-whiplash scenario,” said Andrew Schwartz, lead scientist at UC Berkeley’s Central Sierra Snow Lab near Donner Summit. “We are going from warm and dry to really intense snow storms, and right back to dry within a few days. It’s been chaotic.”
With dry weather forecast for the next two weeks, the chances are low of reaching 100% of normal by April 1, typically the date that ends California’s winter snow season, Schwartz added.
“We have a long way to go to get back to average, and not much time to do it,” he said. “The likelihood of big storms coming through in the second half of March and April is not high.”
In prior years water managers in cities and farm communities throughout California would have been nervous. But after a rare three wet winters in a row leading up to this year, reservoirs across the state began the winter with more water than normal and now are near full.
On Thursday every major reservoir in California was above its historical average. The largest, Shasta, near Redding, was 82% full, or 115% of normal; the second largest, Oroville, in Butte County, was 83% full and 129% of normal. San Luis, east of Gilroy, was 84% full and 105% of normal; and Southern California’s largest reservoir, Diamond Valley, in Riverside County, was 94% full and 127% of normal.
“The good news is that our reservoirs are in good shape,” said Jeff Mount, a professor emeritus at UC Davis and senior fellow at the Public Policy Institute of California Water Center in San Francisco.
“That’s our buffer. It is unlikely we will be seeing water restrictions this summer,” Mount added. “I don’t hear a lot of drought talk. But what happens next year matters. We’ll draw our reservoirs down and hope for the best next winter to keep them topped up.”
Mount and Schwartz agreed that if the Sierra Nevada snowpack is only about half its historical average by April 1, wildfires are probably more of a concern this summer than water shortages.
“Snowpack is so critical to maintaining soil moisture,” Mount said. “Without it everything dries out earlier. Low snowpack is a proxy for an earlier and longer and possibly tougher fire season.”
In years when California has had many major snow storms, summer wildfire season is delayed also for the simple reason that much the mountains and foothills are covered with snow later into the spring and early summer, and snow doesn’t burn.
This year, warm temperatures have been a major factor.
From November through the end of January, much of the American West, and large portions of the Sierra Nevada experienced their hottest temperatures since modern weather records began in 1895, about 3 to 6 degrees Fahrenheit warmer than the average from 1991 to 2020, according to data from NOAA, the National Oceanic and Atmospheric Administration.
So when storms were able to break through, much of the precipitation fell as rain instead of snow. And although none of California is experiencing drought conditions, according to the U.S. Drought Monitor, a weekly federal report issued every Thursday, all the other Western states are suffering through some level of drought, with conditions in Colorado and Utah particularly bad.
“We are going to be hearing a lot about worsening water crises on the Colorado River this summer, as well as about large forest fires in the Rockies and possible Cascades,” said Daniel Swain, a climate scientist with the University of California’s California Institute for Water Resources.
Water shortages on the Colorado River, which flows through seven Western states and includes two massive reservoirs, Lake Mead and Lake Powell, affect California, because the river and the reservoirs provide water to Los Angeles and other Southern California cities, along with irrigation water to Imperial County. When Southern California has limited Colorado River supplies, it puts more pressure for water to be pumped from Northern California through the Sacramento-San Joaquin River Delta, Mount noted.
Climate change appears to be playing a role in the all-or-nothing conditions California is seeing, Swain said.
“There are clear climate links to the record warmth, and the generally low and variable snowpack,” he said. “And modest evidence linking the recent “whiplashiness” and record-breaking rain events to warming as well.”
In addition to hotter weather that melts snow, warmer conditions often bring bigger more drenching storms and blizzards when they do occur, because more water can evaporate into storms from the Pacific Ocean. Climate studies that Swain and other scientists have published in recent years say more “weather whiplash” with drier dry periods and wetter storms, are likely to increase as the climate warms in coming decades.
“I actually just received a photo from someone in South Lake Tahoe this morning who received 3-4 feet of snow last week,” Swain said. “And it is now already completely melted.”
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