Nearly a season's worth of rain in February alone

 

Image: Data maps from NOAAView show estimates of California rainfall in February, 2015, 2016, and 2017. As evident from the deeper blue image on the right, California received far more rainfall this year than during the two previous years. This type of data, estimated from polar-orbiting and geostationary satellites, are especially critical in monitoring offshore precipitation events before they affect land. Credit: NOAA Environmental Visualization Laboratory

 

 

 

After a severe, multi-year drought, the massive amounts of moisture brought a striking turnaround in the extremely low water levels in California reservoirs.

 

At Lake Oroville north of Sacramento, which serves as California’s second-largest reservoir, water levels reached 100 percent capacity in early February, nearly 50 percent higher than the expected seasonal level.

 

Image: Aerial view looking southwest over California’s Feather River on Feb. 26, 2017. In the distance are the Sutter Buttes, a complex of eroded volcanic lava domes rising above the flat plains of the Sacramento Valley. This year's record rainfall and snow brought river levels to the brim. Photo by Kelly M. Grow, California Department of Water Resources

 

 

 

Water poured in at the highest level since 1997

 

Image: Daily average inflow to Oroville Reservoir from Jan. 1, 1995 to Feb. 13, 2017. Credit: NOAA Climate.gov graph based on data from California Department of Water Resources

 

 

At the Oroville Dam, which at 770 feet is America’s tallest dam, a crisis hit as water surged over deteriorated areas.

 

About 180,000 people living downstream from the dam had to be evacuated when, for the first time since the early 1960s, an emergency “spillway” was used to lower the water level. Numerous Central Valley and Northern California rivers and creeks topped flood levels. 

 

Image: Aerial view of the Oroville Dam on June 23, 2005, and water surging through a gully on Feb. 11, 2017. Photos (top) Paul Hames and (bottom) William Croyle, both of California Department of Water Resources

The NOAA National Weather Service continues to provide essential support. Throughout the crisis, NWS’s Western Region Regional Operations Center provided daily forecasts to the California Governor’s Office of Emergency Services and FEMA’s team. 

 

Coordinating closely with government partners at all levels, NOAA river forecasts, on-site weather forecasts at Oroville Dam, briefings to the National Business Emergency Operations Center, and hydrology services for flood operations were all steadfast NOAA components in the race against nature. 

 

On Feb. 12, 2017, NOAA’s Sacramento’s Weather Forecast Office issued a Flash Flood Warning supporting emergency evacuations. Reservoir managers had vital planning support. NWS was prepared to meet aerial imagery needs. NOAA’s California-Nevada River Forecast Center was ready to fulfill forecast and briefing requests 24/7.

Throughout the crisis at Oroville Dam, NOAA hydrologist Cindy Matthews provided expertise at the California State Flood Operations Center. Cindy ensured accurate, rapid communications between first responders and the NOAA National Weather Service. She is shown here briefing John Paash, of the California Department of Water Resources, during emergency activation.  

 

 

 

 

 

 

 

 

Most heavy precipitation in California comes from “atmospheric rivers,” or narrow bands of enhanced water vapor transported by storms forming over the Pacific. Strong winds push this airborne water vapor up mountain sides, forcing it to condense and fall as snow or rain. 

 

In a typical winter wet season, California experiences about six atmospheric rivers. This year there have already been 21.

 

As shown here, storm clouds that interact with atmospheric rivers can be detected by satellite. For the heavy California rain and flooding, NOAA’s GOES-West Satellite in Rapid Scan Operations tracked important features in the clouds and atmosphere more frequently than would have been possible in a normal satellite scanning mode, enabling forecasters to examine evolving storm systems in greater detail and more quickly make assessments and predictions.

 

Image: This animation of visible and infrared imagery from NOAA's GOES-West satellite shows a series of moisture-laden storms affecting California from Jan. 6 through Jan. 9, 2017. Credit: Dennis Chesters, NOAA/NASA GOES Project

 

NOAA scientists developed this Total Precipitable Water (TPW) product, which blends multiple satellite TPW products, as well as some land-based observations to reveal how much water vapor in the atmosphere might turn into precipitation. Most atmospheric moisture is below 10,000 feet. TPW measures the amount of moisture in the air that could be condensed as liquid, serving as a vital heads-up for potentially deadly flooding and other hazards. Image: Limin Zhao, NOAA

 

Because atmospheric rivers can also be unpredictable, NOAA Research and the California Department of Water Resources further monitor them with a state-of-the-art observing network. Several instruments help forecasters detect storm conditions that affect the watershed above Oroville Dam.

 

A cost-effective, snow-level radar developed by NOAA’s Earth System Research Laboratory measures where falling snow changes to rain above the dam. This distinction is critical. Rain falling on snow or bare ground increases immediate flood threats, while snow falling in the watershed stays in place until it melts.

 

Image: Example of the snow-level radar data product that gives forecasters information about surface temperature and the level in the atmosphere where snow changes into rain. Credit: NOAA/ESRL. (inset photo) Snow-level radar and associated monitoring equipment at the base of California's Oroville Dam. Photo by Clark King, NOAA

 

NOAA meteorologists Allen B. White and Lisa Darby study observations from six of the snow-level radars located in central and northern California, including one from Orville Dam. The snow-level radar is part of a much larger California observing network of state-of-the-art instruments installed by NOAA to help scientists and decision-makers better understand the causes and impacts of winter storms. 

 

California State climatologist Mike Anderson says, "This ongoing collaboration greatly facilitates our flood planning and response efforts, integrated water management, and climate change tracking activities in California."

By late February, the California Governor's office was already estimating that flood damages associated with this winter's heavy rains could top $1 billion.

 

Photo by Barbara Deluisi, NOAA

In a remarkable effort to manage vital resources while ensuring public safety during the Oroville Dam crisis, NOAA Fisheries' West Coast Region supported state agencies in evacuating six million hatchery fish from dangerously murky waters. 

Two million state and federally-listed threatened spring-run Chinook salmon and four million fall-run Chinook salmon were evacuated and moved to safe harbor downstream from the dam until conditions improved.

One million spring-run Chinook have since been safely released into the river.  

Since murky water can smother eggs, NOAA biologists and state engineers devised an alternative water supply for steelhead eggs too sensitive to move from their hatchery. The initial system used a fire hydrant and makeshift charcoal filtration system to remove chlorine, a serious threat to egg survival.

Fish being safely released. Photo by California Department of Water Resources. (inset photo) Juvenile Chinook salmon raised in a California hatchery. With the aim of restoring the San Joaquin River with spring-run Chinook, the parents were also raised in a hatchery. Photo by Jim Milbury, NOAA

There’s also positive news and a caution from California’s epic winter. Developed by NOAA and our partners, the U.S. Drought Monitor shows that, in late February, California drought was at just 17 percent. Last year this time it reached 95 percent. 

 

The key to recharging streams, lakes, rivers and reservoirs is snow melt and, as of late February, snow in the Sierra Nevada Mountains was the heaviest it’s been in over two decades. When the snow melts, it will provide one-third of California’s freshwater supply.

 

The caution pertains to both infrastructure and climate. Both require attention. Events such as the near devastation in northern California are a reminder that, in a warming world, heavy downpours are expected to increase as greenhouse gases continue to rise, and resilient infrastructure becomes ever more important to lives, livelihoods and our American quality of life.

 

Image: This animation of the U.S. Drought Monitor provides a 12-week picture of conditions nationwide and for specific geographic areas. It draws on a convergence of vital scientific evidence, including crop conditions, standardized precipitation, soil moisture, mountain snow pack, and many other indicators and data. Credit: National Drought Mitigation Center