Atmospheric River Reconnaissance: Mission Planning, Execution, and Incorporation of Operational and Science Objectives

Accurate forecasting of atmospheric river (AR) landfall is vital for western U.S. water management and flood risk mitigation. To address observation gaps and improve forecasts, the AR Reconnaissance (AR Recon) program was created as a research and operations partnership (RAOP) led by the Center for Western Weather and Water Extremes (CW3E) and the National Oceanic and Atmospheric Administration (NOAA), with participants from international, federal, and state agencies, universities, and industry. This paper summarizes AR Recon planning processes, targeted sampling strategies, forecast impacts, scientific advancements, and lessons learned, and also highlights benefits for water management and flood risk reduction. Since 2016, AR Recon has used NOAA and U.S. Air Force aircraft to release dropsondes over the North Pacific, collecting meteorological data for real-time operational use and research. Complementary observations include airborne radio occultation, radiosondes launched from the West Coast, and barometer-equipped drifting buoys alleviating oceanic data gaps. From November to March, when an AR is expected to affect the West Coast within approximately a week, AR Recon initiates daily forecast meetings with a forecast briefing, quantitative tool synthesis, and flight track design. Flights are tailored to sample essential atmospheric structures (e.g., AR cores, edges, jets, troughs, vorticity anomalies, mesoscale frontal waves, and extratropical cyclones). Ensemble and adjoint sensitivity tools support flight planning. A Mission Director guides the decisions on whether to fly and where, emphasizing targeting of essential atmospheric structures and considering operational benefits and science objectives. This RAOP approach enhances forecast accuracy in the western United States and beyond, and advances science.