By Andrew Schwartz

Few people, if any, would have made the prediction in September 2022 that the upcoming winter would be contending for the top spot among the snowiest seasons on record. Three consecutive years of winters underperforming had left even the most optimistic expecting another dry and warmer than average winter that would contribute to further drought. Fortunately, this winter has been nearly the exact opposite of what was expected, with cold temperatures and deep snow that at times has been trying even for the hardiest and most seasoned of us.

Discussion has turned away from record-low reservoir levels and increasing water restrictions to record-high snowfall and snowpack water storage, often with nearly daily mentions of records being broken. But, what do these extremes actually mean, how can we put them in context, and, perhaps most importantly, what are the implications for our water resources and their impacts on the drought?

RELENTLESS RIVERS: Location, date, and severity of landfalling atmospheric rivers from Oct. 1, 2022 through March 28, 2023. These weather events have provided the bulk of rain and snowfall for California and have led to one of the wettest years across the state. Graph by Chad Hecht, meteorologist at the Center for Western Weather and Water Extremes at Scripps Institution of Oceanography, UC San Diego

When discussing where this year ends up in terms of records, it’s important to consider how we make and compare measurements in science. In a location like Donner Summit, where Central Sierra Snow Lab (CSSL) is based and where this author studies the snow, there is an abundance of history and records that go back well into the 19th century and beyond. The high importance of this region as a travel route means that measurement of snowfall and record keeping was the difference between safe or, in a few well-known instances, unsafe passage through the region in winter. As a result, Donner Summit has a wealth of weather records, particularly snowfall and snowpack, but that’s not to say they’re all directly comparable.


It’s no secret that weather can be dramatically different even over short distances; anyone who has skied deep powder in the valleys and ice at the summit after a storm can tell you that. But it’s also something that we need to take into account when examining weather records. Even though Donner Summit may seem relatively small compared to the Sierra Nevada, differences in where snowfall measurements are taken on the summit can produce wildly different results, and differences in methods for measuring snow can make comparisons between years even more complicated. As an example, prior to when the CSSL was built in 1946, the Union Pacific and Southern Pacific Railroads took the measurements near the railroad snow tunnels, as often as every hour if there was new snow. By comparison, the CSSL checks measurements of new snow daily at 8 a.m. and 4 p.m., much less frequently, and that creates an issue when trying to make apples-to-apples comparisons prior to and after 1946.

STRONG SECOND: This bar chart shows the top 10 snowiest winters as measured by the UC Berkeley Central Sierra Snow Lab since 1946 with winter 2022/23 in second place. Graph courtesy UC Berkeley Central Sierra Snow Lab

Here’s why: Snow settles after it has fallen, with the space between snowflakes on the ground gradually shrinking over time, so that even though the amount of snow and water stays the same, it will become more compacted and appear less deep. Snowfall measurements taken every hour are more likely to be lighter, fluffier, and greater than those obtained a couple of times each day, leading to the railroad records prior to 1946 likely showing higher amounts of snowfall compared to the CSSL’s measurements — a bias in the record. Neither method is wrong, as long as the measurements were carried out consistently, it just means that they can’t be directly compared. This is why, even though snowfall records on Donner Summit go all the way back to 1878, the CSSL only provides official comparison of snowfall totals and maximum snow depth back to 1946. It’s also the reason that there seems to be an assortment of statistics that all have this winter at slightly different places in the rankings.

At the time of writing, this season is the second snowiest season ever recorded at the CSSL (since 1946), with 722 inches of snowfall since October 1, 2022, putting it well above the infamous winters of 2010/11 and 1982/83, by 79 and 51 inches, respectively. At this point, the only winter with more snowfall was 1951/52 at a whopping 812 inches (67.7 feet), but there’s a caveat to the snow that we’ve had this winter. Much of it came during the colder-than-average storms at the end of February and beginning of March, bringing a lot of light and fluffy snowfall. While great for skiing and impressive to see as it continued to pile up and push this year above other deep years, the colder temperatures during these storms meant that the snow didn’t contain as much water as if a similar amount had fallen in a warm storm.

Prior to this massive winter, when the first flakes of snow fell in October and excitement about a potentially big season grew as storms dropped deep snow in December, a familiar question was often asked: How much snow do we need to end the drought? The answer at the time, informed by recent water research and modeling meetings, was an extra year’s worth of rain and snow — something that has only happened a few times since record keeping began, and only when weather patterns favor lots of precipitation from atmospheric rivers.

These bands of concentrated water vapor in the atmosphere perform much like rivers on the surface of the planet. They bring moisture from warm tropical regions to the west coast of North America and other regions around the world, and they’re vital to California’s water supply. Often, water modelers and managers in the state refer to five or six storms that can make or break a season because of the immense amount of rain and snowfall that can be dumped from a single atmospheric river. This year, the west coast of North America has seen 31 rivers in the sky with 17 making landfall in California and depositing plenty of water in our snowpack.

Snow Water Equivalent (SWE) is the amount of water that can be obtained by melting the snowpack and is, generally, the most important measurement of snowfall and snowpack because it informs us about how much water is stored. Although this year’s snowfall has been one of the highest on record here at the lab, the amount of SWE has been lagging behind other deep years due to the light snowfall earlier in the season. Statewide, however, we see a much different picture with Southern California’s snowpack approaching nearly triple the volume normally seen at April 1, and Central and Northern California still being well above average.

The April 1 SWE measurements from around the state are the most important metrics of the year because they are observed when snowpack is at its highest and thus provide the most information for water managers regarding water availability for the upcoming year. They showed that the snowpack SWE was 233% of average statewide, which is one of the highest values in the history of the snow survey program and has largely been boosted this year by the record-breaking snow at many locations in the southern Sierra Nevada. Closer to home, at the Donner Summit Snow Survey location, this winter provided the biggest measurement of April 1 SWE since 1983.

WIDESPREAD IMPROVEMENT of conditions has occurred throughout the state with many regions now completely out of drought based on the most recent U.S. Drought Monitor. Courtesy graph

So, here we are, six months after the season started with nearly double the CSSL’s average annual snowfall and many places in the state double or even triple their average annual rain and snowfall — exactly what was suggested to resolve the drought. And that’s precisely what we’re witnessing. Widespread improvement of drought conditions has occurred throughout the state and large regions (including Truckee, Tahoe, and the surroundings) are now completely out of drought based on the most recent US Drought Monitor. Lake Tahoe is currently at its highest level in nearly two years and will continue to fill once snowmelt around the Basin makes its way down from the peaks. These are the improvements that we were all hoping to see at the beginning of the season, but thought to be out of reach.

It hasn’t been easy, though. The struggles of a big winter have been apparent throughout the region with snow loads that have caused the roofs of some homes and businesses to collapse, persistent chain controls and frequent road closures, and the challenge of continually shoveling snow even when there no longer appears to be any place to put it. The seemingly ever-growing snow berms on roadsides and parking lots have resulted in a perpetual game of ‘am I following the law or not?’ for those of us that haven’t taken the time to memorize each sign location and text. It has been enough to make many of us question whether it’s possible to have too much of a good thing even after years of severe drought. More often than not the answer seems to be that the big snow piles and the water contained in them is better than the alternative of another year devoid of the water we so desperately need.

This has been the winter that many of us had hoped for over the last several years. We have finally had an abundance of rain and snow, reservoirs and lakes have refilled and (broadly) are at or above average, and the number of powder days has been insane! The massive snowpack should provide moisture for forests and ecosystems into July and even August, potentially staving off some of the extreme fire danger we’ve seen so frequently in recent summers. Does this mean that our water woes are completely over? No. Water in the southwestern U.S. is too complicated to be solved by one great season, but this year couldn’t be better for water and our snow. It’s the winter that you tell your children and grandchildren about in tales about your back problems (see Have You Lost Your Bounce?) or (more fondly) of getting in those chest-deep powder days. The one that tested even the most hardened of winter lovers, if only for a moment. The one that has allowed us a glimpse of optimism after years of pessimism. One that will, undoubtedly, remain in the minds of those who lived through it for eternity. Winter 2022/23 — the deepest in 71 years and one for the record books.

~ Andrew Schwartz is the lead scientist of the UC Berkeley Central Sierra Snow Lab. He holds a Ph.D. in Atmospheric Science from the University of Queensland where he studied the impacts of burned forests on snowpack processes. He received his B.S. from MSU Denver where he majored in meteorology.


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