This year, AR Recon is taking the first step toward expanding its reach farther west across the Pacific by testing flight operations from Guam for a two-week period. This adds to the Air Force aircraft stationed in California and the National Oceanic and Atmospheric Administration (NOAA) Gulfstream IV (G-IV) jet stationed in Hawaii, which could facilitate even earlier warnings of incoming severe rain and snowfall. The 2023-2024 campaign also features a longer season of potential flights, new sensors aboard the aircraft, and the deployment of more than 80 additional drifting ocean buoys.
"The AR Recon partnership is a great example of state, federal, and academic collaborative research using emerging technologies to improve California's ability to manage water with increasing weather extremes,” said Michael Anderson, state climatologist with the California Department of Water Resources (DWR). “This critical research allows for DWR to use new innovative strategies for water management in a changing climate."
The opening November window for forays into the skies over the Pacific comes as the traditional rainy season begins and with
El Niño conditions in the Pacific Ocean, which can create a more active North Pacific storm track and steer more storms towards Southern California.
Despite the importance of accurately forecasting where atmospheric rivers will make landfall and how strong they will be, doing so is challenging with traditional sources of meteorological data such as weather satellites, which often cannot measure the key patterns of water vapor, wind, and temperature within atmospheric rivers.
“If you want to predict where a car is going to be five minutes from now you need to know where it’s starting from and how fast it’s moving,” said
Marty Ralph, a research meteorologist at UC San Diego’s Scripps Institution of Oceanography and founding director of Scripps’ Center for Western Weather and Water Extremes (CW3E). “Similarly, if there is an atmospheric river out near Hawaii, and we want to forecast where it will hit the California coast a few days later and how strong it is, we need to get out there and take direct measurements.”
Ralph leads the AR Recon program along with Vijay Tallapragada, Senior Scientist at NOAA’s
Environmental Modeling Center. The program’s partners include the U.S. Army Corps of Engineers, the California Department of Water Resources, NOAA Office of Marine and Aviation Operations, and the U.S. Air Force Reserve 53rd Weather Reconnaissance Squadron.
"Data collected by NOAA’s G-IV and the U.S. Air Force’s WC-130’s during an unprecedented series of ARs in January 2023 contributed to more than 10% improvement in National Weather Service (NWS)
Global Forecast System precipitation forecasts especially over the Central California and other regions impacted by landfalling atmospheric rivers," said Tallapragada.
Rivers in the sky
Atmospheric rivers form when winds over the Pacific send
a ribbon of warm, moisture-laden air toward the West Coast. These rivers in the sky flow at altitudes mostly below 10,000 feet altitude and can measure 500 miles across and 2,000 miles long. When an atmospheric river hits mountains, such as California’s Sierra Nevada, it is forced even higher in the atmosphere where cooler temperatures condense its vapor, rapidly transforming it into huge amounts of rain or snow concentrated over one to three days.
The average atmospheric river carries an amount of water vapor roughly equivalent to 25 times the average flow at the mouth of the Mississippi River, but severe atmospheric rivers can transport even more. The intense rain and snow storms caused by atmospheric rivers can account for up to half of California’s annual rainfall.
Atmospheric rivers are expected to become stronger as human-caused climate change heats up the globe, because hotter air can hold more moisture, said Ralph. Climate models also suggest that dry spells between these intense bouts of precipitation are likely to become more pronounced,
ping-ponging California between bouts of extreme weather and creating what some call “ weather whiplash.”
Planes, buoys, and balloons
The aim of AR Recon is to “fill in information gaps with direct observations of atmospheric rivers and improve forecasting to inform Western decision-makers regarding storm impacts, water management, and flood mitigation,” said Anna Wilson, Field Research Manager at Scripps’ CW3E and AR Recon coordinator. Advanced warning can help
reservoir operators to manage water levels or help state and local officials issue warnings to areas at risk of flooding, she added.
The AR Recon program has expanded since its first flights in 2016 as its data has been shown to improve forecasting. Last year, AR Recon data improved three-day lead time forecasts of heavy precipitation over California by up to 12% – a level of improvement which roughly equates to 8 additional years of honing forecast models with traditional methods.
The core elements of the AR Recon program are the U.S. Air Force Reserve’s
WC-130J Super Hercules aircraft and NOAA’s Gulfstream IV. Each of these aircraft are outfitted to fly into and above intense weather to collect huge amounts of meteorological data.
The primary way the aircraft collect these data is by dropping about thirty cylindrical instruments called dropsondes into the atmospheric river in each flight. Each dropsonde has a small parachute and as it floats down to the ocean it collects and transmits data back to the aircraft including air temperature, pressure, water vapor, and wind speed. The dropsondes are “a bit like an MRI for an atmospheric river, they let us see the internal structure,” said Ralph.