Several moisture-laden storms supplemented water levels at many of California's major reservoirs last month, though some still fall behind by comparison to this time last year.
A bomb cyclone brought dangerous weather conditions across the Pacific Northwest last month, causing power outages for more than a half-million people and killing at least two. Several atmospheric rivers pummeled California at about the same time.
A bomb cyclone occurs when a storm's pressure drops quickly, which intensifies the storm and ramps up wind gusts. Atmospheric rivers are a "long, narrow region in the atmosphere—like rivers in the sky—that transport most of the water vapor outside of the tropics," according to the National Oceanic and Atmospheric Administration.
The deluge contributed to a sudden rise in several California reservoirs, including Lakes Shasta and Oroville, the state's two largest reservoirs. The California Department of Water Resources (DWR) publishes a daily graphic depicting the performance of 17 of the state's major reservoirs. Some of them are highlighted below.
Lake Shasta Water Levels
Lake Shasta, California's largest reservoir, is in the northern part of the state. It reached concerningly low levels following a yearslong drought that affected the Golden State. But its levels recovered significantly during the 2023 water year, which began in October 2022. Much of the recovery was attributed to multiple atmospheric rivers that hit the state that winter.
As of Wednesday, Lake Shasta's water level elevation was at 997.57 feet, 69.43 feet below full capacity. The lake saw a stark increase during November from the heavy rain that hit California, though its levels are still behind where they were on December 4, 2023.
The most recent DWR data shows Lake Shasta is at 61 percent capacity, which is 113 percent of its historical average. This time last year, Shasta was at 67 percent capacity, or 124 percent of its historical average.
Lake Oroville Water Levels
Lake Oroville, California's second largest reservoir, also saw a significant increase during November, nearly 18 feet, one of the biggest water level changes the lake has ever seen during November.
Despite rising earlier than it has in recent years, Lake Oroville had higher water levels this time last year. Recent DWR data shows Oroville is currently at 56 percent capacity, or 109 percent of its historical average. Last year on December 4, Oroville was at 68 percent capacity, or 132 percent of its historical average.
"For the 2024 Water Year, Lake Oroville saw steady increases starting mid-December 2023, with higher elevation gains in late January 2024 due to weather," a DWR spokesperson told Newsweek. "Half of California's annual precipitation falls December through February, making those the key months for water managers."
Trinity Lake Water Levels
Other lakes are performing better this year than they did last year.
Data from Monday shows Trinity Lake was at 68 percent of its capacity, which is 118 percent of its historical average. The lake, which is in northwest California, experienced steady increases during the atmospheric rivers in November.
Last year, Trinity Lake was lower, at only 49 percent capacity, 86 percent of its historical average.
Diamond Valley Lake Water Levels
Diamond Valley Lake in southwest California also is performing better this year. Data from Monday shows the lake is nearly full, at 97 percent capacity, or 140 percent of its historical average. The lake also performed above average in 2023, though it was at only 90 percent capacity at this time of year.
Millerton Lake Water Levels
Millerton Lake in Central California has seen an increase in its water levels, compared with this time last year. Though it is still performing below average, recent data shows the lake at 40 percent capacity. This time last year it was at 36 percent capacity.
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