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Measurements adopted across the Sierra Nevada show that snow packs in California, which typically provide nearly a third of the state’s water supply, are now at 85% of the average for this period.
Additionally, the latest status data shows that the amount of snow in the mountains varies dramatically from region to region. The Northern Sierra has a lot of snow in most areas, while the Central and Southern Sierras are much less than average. This brought Northern California, leaving Southern California dryers, when it brought Southern California heaviest atmospheric river storms.
In addition to these primarily random weather conditions, scientists also see trends related to human-focused climate change. This year’s snowman is significantly smaller at many low-elevation sites in the mountains after months of warmer than average.
“It’s a really warm temperature signature,” said Daniel Swain, a climate scientist at UCLA. “There was a lot of rain in the mountains, but it’s more like rain than snow for most of the season.”
Crossing the central and southern Sierra Mountains, average temperatures over the past three months ranged between 2-5 degrees Fahrenheit F, than the 30-year average. Swain said that snow buildup is less in areas below about 7,000 feet above sea level, despite some high lift locations recording above average snow.
In a study published in 2023, scientists predict that if snow lines in California mountains have already crept in high due to rising temperatures and do nothing to slow the pace of global warming, the mountain could lose more than half of its seasonal snow cover.
Swain said the shift to lower elevation snow was “what we’ve seen more and more in warmer climates,” highlighting the ongoing need for California to change the way it adapts to water.
The current snow pack levels that state water managers will discuss in their monthly snow survey on Friday represent one of several metrics for measuring California’s water surface. The other is the amount of water stored in state reservoirs, well above average levels.
The extremely rainy weather of 2023 and moderately wet 2024 filled the reservoir. At the time, California’s water storage supply was in a relatively good shape towards spring and summer.
Lake Shasta, the state’s largest reservoir, is located at 78% of its capacity, with the second largest lake Oroville at 84%. Both reservoirs are expected to fully fill spring as they are replenished with rain and run out of the rain.
Other large reservoirs from Lake New Melons to San Luis Reservoir are similar to those above average levels during this period.
“We’ve had two previous rainy years so we’re in good condition,” said Jeffrey Mount, a senior fellow at the Institute of Public Policy at the California Water Policy Center.
Southern California’s Metropolitan Water District provides supply to 19 million people across six counties, with 3.8 million acre feet of banks depositing in various reservoirs and underground storage facilities. This is about three times the total amount of water the district has supplied each year in the past few years.
“At this point, there is no immediate concern about the city’s water supply,” Swain said.
The snowpack is below average, but has improved after a series of atmospheric river storms. A month ago, Sierra Snowpack averaged just 65%.
More storms are expected to arrive in early March, bringing more rain and snow before the rainy season ends. Swain said it appears to be a “decent storm cycle.”
Throughout winter and early spring, state water officials use a network of snow sensors combined with manual investigations throughout the Sierra Nevada to measure snow packs. The final snow survey of the season is scheduled for around April 1st, when snow usually reaches its peak.
This winter, atmospheric river storms followed things like “corridors” in Northern California and southern Oregon, Swain said.
This has created a permanent pattern of unusually wet, snowy weather in Northern California and unusually dry weather in most of Southern California and the Southwest. Swain said the current state of La Niña, a cool phase in the tropical Pacific waters cycle, probably contributes to this pattern.
As of Thursday, snowpacks in the northern Sierra measured 106% of date average, compared to 81% in the central Sierra and 69% in the southern Sierra.
“There’s a huge gap from north to south,” Swain said, adding that this pattern of north-south “dipole” is likely to last.
This week, the US drought monitor website shows that almost 42% of states covering Southern California and the San Joaquin Valley are experiencing at least moderate drought conditions.
Drought conditions in California
About 25% of the state experienced at least moderate drought on February 25th. This has increased over a year ago when there is no drought in the area.
There is no drought
It’s abnormally dry
Moderate drought
Serious drought
Extreme drought
February 27, 2024
February 25, 2025
US drought monitor
Los Angeles Times
There is also a continuing severe drought throughout the Colorado River Basin, another major source of water that Southern California cities and farms rely on. Lake Mead, the river’s largest reservoir, is 35%, and snowmen in the Upper River Basin of Colorado is below average this year.
Over the coming months, Swain said the drought situation is likely to spread and intensify across the lower Colorado River and across Southern California.
However, he said snow and rain elsewhere would likely limit drought progress in central and northern California.
“If we start to enter another drying period and the reservoir levels are still above average, that’s good news,” he said.
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