Southern sierra snowpack hits 300% of April average

Department of Water Resources conducts fourth snow survey this year, shows Southern Sierra Nevada’s at record breaking 300% of April average snowfall levels

LAKE TAHOE – After the Southern Sierra snowpack has reached record breaking levels, how fast the runoff will melt is dependent upon Spring weather.

The Department of Water Resources (DWR) conducted their fourth snow survey of the year on April 3 and the report showed snowpack levels are on par with being the highest they have ever been. DWR’s electronic readings from 130 snow sensors placed throughout the state indicate the statewide snowpack’s snow water equivalent is 66.1 inches, or 237% of average for this date. The size and distribution of this year’s snowpack is also posing severe flood risk to areas of the state, especially the Southern San Joaquin Valley. However, the rate at which the snowpack will melt is still unknown and will have to be judged consistently in the coming weeks.

“On a weekly basis, as we get weather forecasting and better guidance, we’ll have a better sense for the rate of runoff,”  DWR supervising engineer David Rizzardo said. “But certainly no holds barred on being vigilant and concerned in terms of the amount of water that we would expect to see coming down.”

Each year DWR conducts about five snow surveys from January through April and sometimes May. This year’s April 1 result from the statewide snow sensor network is higher than any other reading since the snow sensor network was established in the mid-1980s. While above average across the state this year, the snowpack varies considerably by region.

The Southern Sierra snowpack is currently 300% of its April 1 average and the Central Sierra is at 237% of its April 1 average. However, the critical Northern Sierra, where the state’s largest surface water reservoirs are located, is at 192% of its April 1 average. For California’s snow course measurements, only years 1952, 1969 and 1983 recorded statewide results above 200% of the April 1 average.

As the Southern Sierra Nevada’s have reached incredible levels, they continue to pose severe flood risks for those especially in the Southern San Joaquin Valley. According to a press release from DWR, their State-Federal Flood Operations Center (FOC) is supporting emergency response in the Tulare Lake Basin and Lower San Joaquin River by providing flood fight specialists to support ongoing flood response activities. The FOC will also provide longer-term advanced planning activities.

According to DWR’s press release, the FOC and DWR’s Snow Surveys and Water Supply Forecasting Unit are helping local agencies plan for the spring snowmelt season. They will be providing hydraulic and hydrologic modeling and snowmelt forecasts specific to the Tulare Lake Basin that are informed by DWR’s snowmelt forecasting tools, including Airborne Snow Observatory (ASO) surveys. However, even with the technology, according to Rizzardo the amount of melt is dependent on a variety of factors.

“How fast that melt or that runoff comes is going to be largely dependent on how many sunny, warm days that we have starting, whether in April, in May or June,” Rizzardo said. “So there’s a lot of factors there.”

An additional factor is that the Climate Weather Prediction Center is still unsure whether the spring is going to be warm and dry or cold and wet. Because it is uncertain, Rizzardo said it will be something DWR will be looking at on a weekly basis to get better guidance, and a better rate of runoff throughout the next few weeks.

According to Sean de Guzman, manager of DWR’s Snow Surveys and Water Supply Forecasting Unit, additional snow courses have been added over the years allowing for more precise snow level measurements. He said because of the changes in technology, it is difficult to accurately compare results across the decades, but this year is definitely one of the biggest since the 1950s.

“This year’s result will go down as one of the largest snowpack years on record in California,” de Guzman said. “While 1952’s snow course measurements showed a similar result, there were fewer snow courses at that time, making it difficult to compare to today’s results.”

Before the snow sensor network was established, the 1983 April 1 statewide summary from manual snow course measurements was 227% of average. The 1952 April 1 statewide summary for snow course measurements was 237% of average.

While winter storms have helped the snowpack and reservoirs, groundwater basins are much slower to recover. Many rural areas are still experiencing water supply challenges, especially communities that rely on groundwater supplies which have been depleted due to prolonged drought. Long-term drought conditions in the Colorado River Basin will also continue to impact the water supply for millions of Californians.

Storms this year have caused impacts across the state including flooding in the community of Pajaro and communities in Sacramento, Tulare and Merced counties. The FOC has helped Californians by providing over 1.4 million sandbags, over 1 million square feet of plastic sheeting and over 9,000 feet of reinforcing muscle wall, across the state since January.

DWR conducts five media-oriented snow surveys at Phillips Station each winter near the first of each month, January through April and, if necessary, May. Given the size of this year’s snowpack with more snow in the forecast, DWR anticipates conducting a May snow survey at Phillips Station. That is tentatively scheduled for May 1.

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