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Atmospheric river storms can deliver up to half of California’s total annual precipitation and cause 90 percent of flooding in the state. From Jan. 23 through March 18, 2020, scientists led by Scripps Institution of Oceanography at UC San Diego, in partnership with NOAA’s National Weather Service, NOAA’s Office of Marine and Aviation Operations, and the U.S. Air Force Reserve 53rd Weather Reconnaissance Squadron “Hurricane Hunters,” will be on standby to fly through these storms over the Pacific Ocean to gather vital data to improve atmospheric river forecasts. Up to twelve storms will be flown during that period, deploying up to three planes per storm.

“With the atmospheric river reconnaissance missions, called “AR Recon,” we are working to improve forecasts of where atmospheric rivers will make landfall, and better understand how much precipitation they may bring, which has impacts on water supply, flood mitigation, and more,” said research meteorologist Marty Ralph, principal investigator (PI) for AR Recon, and director of the Center for Western Weather and Water Extremes at Scripps Oceanography. “The data captured during these flights makes an immediate improvement on forecast models.”

The challenges to forecasting atmospheric rivers have been partially attributed to a limitation in current real-time observations within the storms, as their location over the Pacific Ocean lacks the ground measurements typically taken over land. A series of studies has shown that data from reconnaissance efforts have significant beneficial impacts on the forecasts. 

James Doyle, senior scientist from the U.S. Naval Research Laboratory Marine Meteorology Division and a collaborating scientist on AR Recon, noted that “data impact studies using the U.S. Navy’s global forecast model NAVGEM demonstrated that the AR Recon soundings have significant beneficial impact, with per observation impact more than double that of the North American radiosonde network. New observations this year will allow for more robust evaluation of the impact on forecasts.”  

The U.S. Air Force Reserve will station WC-130J Super Hercules aircraft at the U.S. Coast Guard Air Station Barbers Point in Hawaii and at Travis Air Force Base in Fairfield, Calif., and NOAA will station its Gulfstream IV-SP jet (G-IV) outside of Portland, Ore. The flights will be scheduled on short notice based on evolving forecasts as atmospheric rivers develop.

“This year marks a major milestone in that the formal National Winter Season Operations Plan, which directs the nation’s airborne weather reconnaissance capabilities at NOAA and Air Force to conduct AR Recon 2020, is using and expanding upon AR Recon methods developed in previous years,” said Vijay Tallapragada, the National Weather Service leader for its global forecast system at the Environmental Modeling Center and co-PI for AR Recon.

During these flights, crew members will deploy dropsondes from the interior of the aircraft at predetermined locations in transects across atmospheric river storms. The dropsondes carry instruments that measure water vapor content, temperature, wind speed and direction, and other variables. These measurements will be used in the National Weather Service’s operational weather forecast models, as well as other major global modeling centers, and to test new methods for improving the prediction of atmospheric rivers and their heavy precipitation on the U.S. West Coast.

Predicting atmospheric rivers is vital to the economic future of California, a state prone to drought that is also one of the most agriculturally productive regions in the world. Better atmospheric river forecasts have the potential to support water resource and reservoir management, reduce flood risk, and be able to better withstand prolonged drought. In December, a study from Scripps Oceanography and the U.S. Army Corps of Engineers found that the total flood damages from atmospheric rivers averaged $1.1 billion annually throughout the West. Scripps Oceanography scientists led by Ralph have also created a scale of atmospheric river intensity to let emergency officials and the public know the potential of atmospheric rivers to bring relatively benign rains or flood-producing torrents.

This marks the fourth year that NOAA and the U.S. Air Force have worked with Scripps Oceanography to observe atmospheric river storms in AR Recon. In 2016, the NOAA G-IV and NASA Global Hawk conducted three research flights as part of the NOAA El Niño Rapid Response field campaign. In 2018, the NOAA G-IV sampled three storms and U.S. Air Force WC-130J Super Hercules aircraft intercepted six atmospheric river storms, and in 2019, another six storms were flown into by the WC-130J aircraft. The increase to up to 12 flights this year significantly enhances the amount of data collected. 

Additionally, more than 50 drifting buoys will be deployed into the Pacific Ocean between California and Hawaii, in partnership with NOAA’s Global Drifter Program, the California Department of Water Resources and the U.S. Army Corps of Engineers. These buoys provide vital sea-level pressure observations in this data-sparse region that are important for numerical weather predictions. 

The forecasting and modeling team that makes decisions on flight planning includes scientists from Scripps Oceanography, 53rd Weather Reconnaissance Squadron aerial reconnaissance weather officers, flight meteorologists from the NOAA Aircraft Operations Center, the National Weather Service, the National Center for Atmospheric Research, U.S. Naval Research Laboratory, the European Center for Medium-Range Weather Forecasts, and additional university partners.

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