California’s snowpack will peak this year at what may be its highest level in modern times, an epic accumulation that has buried the drought in the history books and, going forward, poses widespread risk of flooding.
State water officials, who are scheduled to conduct their traditional April snow survey on Monday, are expected to find more than 235% of average snowpack for the month in the Sierra Nevada and southern Cascades.
The last time California had a similar amount of snow was 1952, when winter storms famously trapped a luxury train near Donner Pass, crushed a mining camp outside Bishop and closed roads across the mountains for months. The snowpack that April measured 237% of average, similar to what this year’s level is approaching, but state officials note the surveys were done differently then.
“It is difficult to compare years across the decades due to the increase in number of survey sites over time, but this year will certainly be in the top,” Sean de Guzman, manager of snow surveys and water supply forecasting for the California Department of Water Resources, said in an email before Monday’s measurements.
The April snow survey in 1983, another big winter, recorded 227% of average snowpack, though the methodology also differed then.
Regardless of how many decades you have to go back to find comparable snow, ski resorts this year will vouch for the current bounty.
Mammoth Mountain Ski Area, one of the snowiest, recently surpassed its previous high of 668 inches of snow at its main lodge. On the summit, it counted 879 inches Friday. Resorts throughout the Sierra will likely stay open into July.
The big winter also has been marked by inconvenience, if not outright hardship.
Communities from the San Bernardino Mountains to Lake Tahoe have been buried in snow for weeks with roofs of homes collapsing, water lines freezing and power lines toppling. An avalanche has closed Highway 395 in the eastern Sierra, north of Lee Vining, since February. Yosemite and Sequoia and Kings Canyon national parks both have had unprecedented shutdowns because of storms.
The state Department of Water Resources conducts its snow surveys every month in winter and spring, but the April measurement is most crucial. It reflects snow levels at their peak, allowing surveyors to gauge how much melt-off will pour from the mountains and provide for cities and farms in the coming year. Nearly a third of the state’s water supply typically comes from snow.
Already, winter storms have lifted the state’s big reservoirs from near historical lows during the drought to mostly above-average levels. Shasta Lake, the state’s biggest reservoir, has risen nearly 120 feet since Dec. 1, more than doubling its volume and, as of this week, was holding 104% of the water it averages at this point in the year.
Most reservoirs, which are much smaller than Shasta, have begun releasing water in order to make room for the anticipated crush of snowmelt.
Concerns of flooding are running high, perhaps greatest in the southern San Joaquin Valley. The mountains nearby have received the brunt of this year’s storms, with the southern Sierra logging a record 298% of average snowpack as of Friday. Already runoff is overwhelming the region’s infrastructure.
A vast lake that once sprawled across the floor of the valley has re-emerged in the Tulare Lake basin, putting farms, roads, homes and even a few small communities under water. The situation is expected to worsen over the next few months as the snowmelt picks up.
The National Guard, Cal Fire and the Department of Water Resources have already begun sending supplies and personnel to assist with the flooding. Gov. Gavin Newsom has requested a presidential disaster declaration to bolster the emergency response.
State surveyors measure snowpack in terms of its water content, not its depth or another metric, in order to best forecast water supplies. Data is collected at more than 260 sites between the southern Sierra and Oregon border, mostly electronically and in real-time so cumulative results can be gauged before the official start-of-the-month manual surveys.
Friday’s statewide snowpack measured 236% of the April 1 average.
On Monday, the state’s measurements at Phillips Station, which has a long and celebrated history of recording snowpack with snow tubes and other instruments, are scheduled. The results will feed into the updated start-of-the-month total.
What has been as spectacular as this winter’s sheer bounty of snow is the fact that it comes after the state’s driest three-year stretch on record.
“This is California’s hydrology,” said Jay Lund, director for the Center for Watershed Sciences at UC Davis and a professor of civil and environmental engineering. “We have more flood and drought years than average years, and the way the climate is changing, we’re probably going to see even more of that.”
Reach Kurtis Alexander: [email protected]; Twitter: @kurtisalexander