Atmospheric river research flights go global
Atmospheric rivers may be associated with wet winter storms on the West Coast of North America, but these ribbons of water vapor in the sky are a global phenomenon. They can end droughts or destroy homes with dangerous flooding, and they are projected to become more intense and destructive. Now, a new international effort will study and forecast these storms on a global scale.
Starting this year, the Atmospheric River Reconnaissance program (AR Recon), led by the Center for Western Weather and Water Extremes (CW3E) at UC San Diego's Scripps Institution of Oceanography and the National Oceanic and Atmospheric Administration (NOAA), will coordinate flights to study atmospheric rivers across both the Pacific and Atlantic oceans.
This expansion of AR Recon, which has studied atmospheric rivers using specially outfitted aircraft over the Pacific Ocean since 2016, is called the Global Atmospheric River and Reconnaissance Program (GARRP). This global program hopes to transform forecasts of extreme weather events and extend reliable predictions beyond the current one-week limit.
"We know that better measurements of atmospheric rivers offshore result in better forecasts and more advanced warnings for severe precipitation," said Marty Ralph, founding director of CW3E and leader of AR Recon who first had the vision to create GARRP. "We expect that combining observations in the eastern Pacific, western Pacific and now the northern Atlantic Ocean will create something greater than the sum of its parts—a potential breakthrough in forecast improvement for extreme weather in the Northern Hemisphere."
What are atmospheric rivers?
Atmospheric rivers typically form over oceans in the tropics and subtropics. Ocean winds cause evaporating water to form into bands of moisture-laden air that flow toward Earth's poles at an altitude that is generally below 3,000 meters (10,000 feet). The average atmospheric river is about 800 kilometers (500 miles) wide and 1,600 kilometers (1,000 miles) long and carries an amount of water vapor roughly equivalent to 25 times the average water flow at the mouth of the Mississippi River. These rivers in the sky release their water when they are forced upward, causing the water vapor to cool, condense and fall as rain, snow or ice.
Atmospheric rivers are powerful: In California, they account for up to 50% of total annual precipitation and more than 80% of flood damages across western states. However, not all atmospheric rivers are dangerous. CW3E developed an AR Scale to classify these storms according to their severity from one through five. Weaker atmospheric rivers, three or less on the scale, can be vital and beneficial sources of freshwater and wildfire mitigation, but storms that are classified a four or five on the scale are primarily hazardous, sometimes causing dangerous floods and debris flows as happened recently in the U.S. Pacific Northwest.
Building on success
GARRP is a vision that expands on the success of AR Recon, which has deployed "Hurricane Hunter" WC-130J Super Hercules aircraft from the U.S. Air Force Reserve 53rd Weather Reconnaissance Squadron and the NOAA Hurricane HuntersGulfstream IV jet to fly into and above atmospheric rivers over the Pacific Ocean for nearly a decade. These flights collect data that are impossible to obtain through satellites, whose view is often blocked by clouds, or via traditional weather instruments, which are sparse in the middle of the ocean where atmospheric rivers typically form. Filling in these information gaps improves forecasts and allows for better decision making to mitigate storm impacts.
The aircraft are equipped with an array of sensors that record the state of the atmosphere as they fly—including a system developed by Scripps researcher Jennifer Haase known as airborne radio occultation—and release cylindrical instruments called dropsondes into atmospheric rivers. The dropsondes collect information on air temperature, pressure, water vapor and wind speed as they descend via parachute. Ralph likened the dropsonde data to an MRI scan of an atmospheric river that reveals its internal structure. AR Recon also collects data with ocean-drifting buoys and two different types of weather balloons released from land.
The data collected by AR Recon, as well as advancements in the computer weather modeling that uses the data, facilitate more accurate forecasts by providing information on how much water vapor an atmospheric river is transporting as well as its speed and direction of travel. More accurate forecasts and more advanced warnings can enhance public safety when flooding is predicted and can support water managers making complex choices before a storm arrives.
During the 2024–2025 rainy season, AR Recon conducted 52 flights deploying more than 1,400 dropsondes across the Pacific.
This season, the U.S. Air Force Reserve WC-130J aircraft are available for AR Recon flights as resources permit from Nov. 1 through March 31, 2026. Beginning Jan. 7 through February 4,2026, WC-130J aircraft will be fully assigned and available for AR Recon based in California and Hawaii.
NOAA's Gulfstream IV jet will fly AR Recon in January and February 2026.
"Data from AR Recon flights have consistently demonstrated improved precipitation forecasts for the U.S. West Coast," said Vijay Tallapragada, senior scientist at NOAA's Environmental Modeling Center and co-leader of the AR Recon project. "With this year's coordinated GARRP demonstration, we're expecting similar improvements across broader regions and with longer lead times. These collaborations are vital for improving precipitation forecasts worldwide and filling critical gaps in atmospheric and oceanic observations."
Going global
This rainy season, GARRP will coordinate AR Recon's Pacific flights with several international campaigns, creating a comprehensive network of observations across the Northern Hemisphere. This year's coordination will demonstrate the added forecasting power of combining observations from these different ocean basins and offer a glimpse of the global program's potential.
"Winter weather in the Northern Hemisphere generally moves from west to east, so if we observe an atmospheric river in the western Pacific off Japan with greater accuracy, that improves forecasts several days later off the U.S. West Coast," said Ralph. "A key hypothesis being tested by GARRP is that the measurements over the Pacific can help with Atlantic forecasts, and observations in the eastern Atlantic eventually propagate around the planet to benefit Pacific forecasts—including the U.S. West Coast where this could support water management decisions."
These campaigns include NASA's North American Upstream Feature-Resolving and Tropopause Uncertainty Reconnaissance Experiment (NURTURE), operating out of Goose Bay, Canada; the international North Atlantic Waveguide, Dry Intrusion, and Downstream Impact Campaign (NAWDIC) led by Germany's Karlsruhe Institute of Technology, operating out of Shannon, Ireland; and the U.S. Office of Naval Research's Sea-Air Fluxes and Atmospheric River Initiation project (SAFARI) program, which placed a moored buoy north of Hawai'i on Nov. 21, 2025.
NAWDIC's research will be conducted using the German high-altitude research aircraft HALO and a French ATR-42 aircraft out of Shannon Airport in Ireland from Jan. 13 to Feb. 20, 2026. This campaign's flights will cover the North Atlantic Ocean with a focus on the atmospheric dynamics that drive high-impact weather across Europe, in addition to releasing dropsondes into atmospheric rivers.
NURTURE will conduct flights using a NASA G-3 aircraft stationed in Goose Bay, Canada, from late January through mid February. These flights will investigate polar and midlatitude upper-atmospheric interactions as well as thermodynamic features over the North Atlantic Ocean using a suite of atmospheric lidar, multi-frequency radar, flight-level trace gas, radio occultation and dropsonde measurements.
"The power of combining these observations comes from the fact that atmospheric rivers are one of the biggest sources of forecast error," said Ralph. "At any given time, there are three to four atmospheric rivers in the Northern Hemisphere—each one is a potential source of error. Coordinating observations across these ocean basins have real potential to compound into a major improvement in our forecasting ability."
This improvement could take atmospheric river forecasts from roughly one week of advanced warning and well into the second week before a given storm makes landfall.
"Having reliable forecasts of extreme precipitation events out to week two will be transformative in terms of mitigating the impacts of severe precipitation and flooding events," said Anna Wilson, CW3E's assistant director for AR Recon. "More time to prepare means fewer negative impacts."
Buoys and balloons
In addition to flights over the ocean, AR Recon will use ships and aircraft to deploy 60 drifting ocean buoys in the Pacific and 50 in the Atlantic. The buoys collect water temperature, atmospheric pressure and wave measurements and send those data to forecasters. These buoys are part of the NOAA-funded Global Drifter Program at Scripps. The buoy deployments have been shown to improve forecasts and are a collaboration between CW3E and the Lagrangian Drifter Laboratory at Scripps led by research oceanographer Luca Centurioni. The Atlantic buoy deployments are also supported by European agencies and the European Center for Medium-Range Weather Forecasts.
AR Recon also releases traditional weather balloons called radiosondes from land during the storms to provide additional context. This season, AR Recon will coordinate weather balloon deployments from seven sites along the U.S. West Coast and from 13 universities across the broader continental U.S. as part of the AR Recon University Coordinated Radiosonde Project.
In addition to radiosondes, AR Recon will coordinate with WindBorne Systems to release another type of longer-lasting balloon called a global sounding balloon. These balloons last for about 10 days on average and can ascend and descend each day by releasing ballast or gas as they are carried to remote locations by the wind. The balloons will take measurements from an altitude of 1 kilometer (0.6 miles) all the way up to 18 kilometers (11 miles).
The data collected by AR Recon's flights, buoys and balloons are sent back to land where it is fed in real-time into state-of-the-art weather models tailored to atmospheric river forecasting. This forecast generation is enabled by the new Advanced Warning of Atmospheric River Extremes (AWARE) supercomputer, operated by the San Diego Supercomputer Center, as well as global weather prediction models.
Recognition
Studies have demonstrated that AR Recon-improved forecasts of atmospheric rivers increased water availability at Lake Mendocino in Northern California in collaboration with the Sonoma Water Agency and USACE, and at the Prado Dam in Southern California. These improvements to reservoir operations come from the multi-agency Forecast Informed Reservoir Operations (FIRO) program, led by CW3E and the U.S. Army Corps of Engineers (USACE), which uses forecasts from AR Recon to help manage water levels in California reservoirs. Depending on the scenario, these more accurate forecasts can inform decisions by reservoir operators to retain additional water, which boosts water availability, or to release water to guard against flooding.
"Improving precipitation forecasts further ahead of time empowers California to take advantage of the water arriving with each storm, improving both our water supply and flood warning capabilities," said Michael Anderson, state climatologist with the California Department of Water Resources, a key partner in the program. "AR Recon provides critical data to make improvements to the forecasts in the face of a changing climate and demonstrates how important and beneficial investments in advanced climate and weather research can be for California and the nation."
In recognition of FIRO's utility for reservoir operators, the recent Water Control Manual update for Coyote Valley Dam and Lake Mendocino in Northern California formally incorporated FIRO into the USACE protocol at Lake Mendocino.
"The U.S. Army Corps of Engineers has spent more than a decade researching how to safely and effectively use forecasts to give water managers more flexibility in their operations through the FIRO program," said Cary Talbot, national lead for FIRO with the U.S. Army Engineer Research and Development Center. "The key in determining FIRO viability at a reservoir is the reliability and accuracy of the precipitation and inflow forecasts.
"The improved forecasts from efforts such as AR Recon are giving water managers up to three additional days of reliable forecast lead time which translates to better decisions about when to release or hold stored water to improve the balance between flood risk management, water availability and ecological benefits provided by USACE reservoirs."
AR Recon's position at the cutting edge of atmospheric river science and as a world leader in converting that science into actionable forecasts led the World Meteorological Organization to add AR Recon to its list of 10 World Weather Research Program endorsed projects last year, and this year the World Climate Research Program made AR Recon an Anchor Project for the Global Precipitation Experiment (GPEX). The GPEX initiative's goal is to improve global precipitation predictions. AR Recon's status as an Anchor Project means it will help coordinate global field campaigns studying precipitation as part of the GARRP demonstration in 2026.
"This is an exciting year," said Ralph. "We will see how much the GARRP concept improves forecasts, and if it does then we will hope to make it an annual program like AR Recon. As weather and precipitation events become more severe, better forecasts become that much more important."
Provided by University of California - San Diego
