Warm Weather Does Little To Melt Massive Sierra Nevada Snowpack

SAN FRANCISCO — Warmer weather has finally arrived in many parts of the state and with it comes the start of the Sierra Nevada snowpack melt. According the latest snow survey completed by the California Department of Water Resources, only about 20 percent of that snow has turned into runoff leaving flooding as a concern for many in the San Joaquin Valley.

"Despite a brief increase in temperatures in late April, the statewide snowpack overall melted at a slower pace than average over the month of April due to below average temperatures early in the month and increased cloud cover," DWR said in a news release following the fifth snowpack measurement at Phillips Station May 1.

The manual survey recorded 59 inches of snow depth and a snow water equivalent of 30 inches, which is 241 percent of average for the Phillips Station location on May 1.

"The snow water equivalent measures the amount of water still contained in the snowpack and is a key component of DWR’s water supply run-off forecast," DWR explained, adding that its electronic readings from the 130 snow sensors placed throughout the state indicate the statewide snowpack’s snow water equivalent is "49.2 inches, or 254 percent of average for this date."

An average of 12 inches of the snowpack’s snow water equivalent has melted since April 3 when DWR recorded the measurement at 61.1.

According to DWR, snow surveys like the one at Phillips Station are critical to planning for impacts of the coming snowmelt runoff on communities.

"DWR uses the most updated technology to gather data from snow surveys, a network of 130 remote snow sensors, and airborne snow observatory data to gather information on current real-world conditions to create the most accurate snowmelt runoff forecasts possible," DWR said.

The runoff forecasts, published through DWR’s Bulletin 120, allow reservoir operators to plan for anticipated inflows and water managers downstream of reservoirs to plan and prepare for flood risks.

San Joaquin Valley faces continued flooding

The historic snowpack came about following a parade of 31 atmospheric river storms that ended the drought in California.

“While providing a significant boost to California’s water supplies, this year’s massive snowpack is posing continued flood risks in the San Joaquin Valley,” DWR Director Karla Nemeth said. “The snowpack will not disappear in one week or one month but will lead to sustained high flows across the San Joaquin and Tulare Basins over the next several months and this data will help us inform water managers and ultimately help protect communities in these regions.”

Governor Gavin Newsom visited the Tulare Basin to tour flood impacts first hand April 25. While there he met with community leaders and emphasized the state’s commitment to supporting and providing appropriate assistance to counties impacted by recent and anticipated flooding this spring and summer, a news release issued by the governor's office said.

Flooding impacts in the region are expected to worsen in the coming weeks as snowmelt escalates thanks to higher temperatures in the Sierra Nevada.

Newsom visited several locations in the Tulare Basin including the Allensworth community center, a project spearheaded by Cal Fire to raise a critical access road to Alpaugh, and a dairy that has been partially submerged by flood water, where he was able to observe the impacts of the flooding firsthand.

“California is here for the Tulare Basin, the Central Valley and all parts of our state still dealing with the impacts of the historic deluge of atmospheric rivers we experienced and preparing for future flooding due to snowmelt,” Newsom said.

According to Newsom, the state's focus is to keep those flooded and threatened communities safe.

"We’re working with our federal and local counterparts to provide on-the-ground assistance and the support locals need," he said. "This weather whiplash is what the climate crisis looks like – and that’s why California is investing billions of dollars to protect our communities from weather extremes like flooding, drought and extreme heat.”

According to the Governor's office, state officials have been on the ground since the storms first started hitting, supporting and coordinating emergency response.

"Now, California is shifting focus to flood prevention and recovery efforts and will support local response in the coming weeks, months and years," the news release said.

Phillips Station sees first measurable snow in May since 2020

DWR reported that the last time there was measurable snow at the Phillips snow course on May 1 was 2020, when only 1.5 inches of snow and .5 inches of snow water equivalent was measured.

“No matter how you look at the data, only a handful of years in the historical record compared to this year’s results,” Sean de Guzman, manager of DWR’s Snow Surveys and Water Supply Forecasting Unit, said. “Survey results from our partners in the California Cooperative Snow Surveys Program and other data, including data from Airborne Snow Observatory flights, allow us to incorporate these data into our models to provide the most accurate snowmelt runoff forecasts possible right now to inform water supply, flood control, and planning.”

According to historical records, only the April 1 measurements from the years 1952, 1969, 1983 and this year were above 200 percent, although it is difficult to directly compare individual years across the decades due to changes in the number of snow courses measured over time, DWR said.

"Due to the impact of climate change on California’s snowpack, since 2021, snowpack averages have been calculated using a timeframe of 1991 through 2020 so that results better reflect the current climate conditions," DWR said, adding that it was maximizing the amount of water that can be stored and diverted from the "record snowpack."

In April, DWR announced a 100 percent allocation of requested supplies from the State Water Project, which delivers water to 29 public water agencies that serve 27 million Californians and 750,000 acres of farmland.

"The last time the SWP allocated 100 percent was in 2006," DWR said.

DWR says it is also maximizing the amount of water that can be diverted towards recharging groundwater basins so more water is stored for future use in underground reservoirs.

"Storms this year have caused impacts across the state including flooding in the community of Pajaro and communities in Sacramento, Tulare, and Merced counties," DWR said, adding that the Flood Operations Center has "helped Californians by providing more than 1.4 million sandbags, 1 million square feet of plastic sheeting, and 9,000 feet of reinforcing muscle wall, across the state since January."