Current weather forecasting tools are less than adequate for managing California’s most vital natural resource, state water officials said Tuesday.

People at the state Department of Water Resources are now working with researchers at NASA and the Scripps Institution of Oceanography to develop new technology to better forecast moisture-laden atmospheric river storms, like the ones that hammered the Mother Lode and the rest of the Central Sierra in January and February.

Current short-term forecasting for seven days out is 70 percent accurate, while 14-day forecasts are 7 percent accurate, Grant Davis, director of the state Department of Water Resources, said Tuesday.

"That isn’t adequate for water management," Davis said. "Advancing accurate, even longer-range forecasting is critical for our ability to plan for California’s highly variable weather."

Atmospheric river storms are the slower-moving freight trains of moisture than can form far to the west of California out over the vast Pacific Ocean. An atmospheric river storm that originates in warmer tropical or subtropical climes is often called a “pineapple express.”

‘Rivers in the sky’

Administrators with DWR like Davis say they are starting the new water year intent on improving subseasonal to seasonal forecasting. Part of that aim is developing new technology for forecasting land-falling atmospheric river storms.

“The water year that ended Sept. 30 saw an extraordinary number of atmospheric rivers that created high water conditions throughout the state,” Maggie Macias with DWR public affairs said Tuesday.

Record-setting precipitation in Northern California and above-average rainfall and snowfall in the Central Sierra contributed to flooding in several river systems. A total of 52 California counties declared states of emergency due to the January 2017 storm sequence.

More atmospheric river storms in February prompted emergency actions by operators of the Golden State’s sixth-largest water storage facility, Don Pedro Reservoir, which used a controlled spillway in February for the first time in 20 years to draw the level down and try to avoid use of a 995-foot-long emergency spillway.

They removed a section of Bonds Flat Road before sending thousands of cubic feet per second ripping into the mainstem Tuolumne River.

Improved forecasting of atmospheric river storms can help public safety agencies and other authorities better prepare for emergencies, as well as manage the vital water that comes to the Central Sierra and the rest of the Sierra Nevada.

New technology

New technology that will help forecasters better model and forecast atmospheric river storms includes the use of wind-profiling radars like a unit installed four years ago at Bodega Marine Laboratory in Bodega Bay in Sonoma County, says Jeanine Jones, and engineer and interstate resources manager with DWR.

“Installation of wind-profiling radars provides data to understand how to model the atmospheric rivers as they reach California,” Jones said in a phone interview Tuesday.

“We are preparing computer models to be able to make experimental forecasts about atmospheric rivers later this winter,” Jones said. “Over the past decade the state of California in partnership with NOAA has spent more than $40 million on an observing system designed to capture these atmospheric river storms.”

The Bodega Bay radar is one of the earliest pieces of the network, Jones said.

Forecasters a decade or more ago tried to work with Nexrad units, also known as Next Generation Radar, that were located on land but aimed too high to see atmospheric rivers, Jones said.

“Now that we have these new observation stations and monitoring equipment,” Jones said, “we can start seeing how to model these storms in weather models and improve forecasting.”

‘What a Difference a Year Makes’

Looking back on the water year that ended Saturday, state Department of Water Resources staff say that after five years of drought, the 2017 water year brought unexpectedly heavy precipitation, ranking second only to 1983, California’s wettest year for statewide runoff.

A recently released report says water year 2017, which started Oct. 1, 2016, and ended Sept. 30, 2017, dramatically illustrated how much California’s annual precipitation can change year-to-year.

“Virtually all of the state experienced at least average precipitation, and key Sierra Nevada watersheds were much above average,” state DWR and California Natural Resources Agency staff said.

Governor Brown lifted the proclamation of statewide drought emergency he issued in 2014, but a state-declared emergency remained in Tuolumne, Fresno, Kings and Tulare counties due to lingering drought impacts, including tapped-out or contaminated groundwater wells.

“Prior to 2017, California had experienced a decade of largely dry conditions,” the report said. “Eight of the 10 preceding water years were dry, and the water years of 2012-15 set a record for the driest consecutive four-year period of statewide precipitation.”

Present forecasting capabilities cannot provide a reliable prediction for the water year 2018, state water officials said.

High annual variability in California’s precipitation means every year could potentially bring record wet conditions like those in 2017, or a return to arid, dry conditions.

It is possible 2017 was “a wet outlier in long-term sequence of otherwise dry years, similar to the persistent dry conditions that have been experienced in the Colorado River Basin for all of the present century,” state Department of Water Resources staff said. “In the absence of reliable predictive ability, Californians must be prepared for the worst in terms of hydrologic conditions even as we hope for the best.”

Contact Guy McCarthy at gmccarthy@uniondemocrat.com or (209) 588-4585. Follow him on Twitter @GuyMcCarthy.

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