Atmospheric River Reconnaissance in Water Year 2023 – A Research and Operations Partnership

Atmospheric River Reconnaissance (AR Recon) is an interagency, international Research and Operations Partnership (RAOP) that collects unique observations in the northeast Pacific to improve AR landfall forecasts and associated precipitation forecasts during the cool season (November – March). Atmospheric rivers (ARs), narrow corridors of intense water vapor transport, contribute 30-50% of the annual precipitation over the western U.S., but are also associated with the majority of flood hazards, especially in coastal areas. Increased demands for actionable information on ARs are driven by additional collaborative interagency RAOPs. An important example is the related Forecast Informed Reservoir Operations (FIRO) RAOP that takes advantage of increased forecast accuracy to support successful management strategies to both conserve water resources and enhance flood protection. FIRO highlights the need to advance weather prediction through improved observations. Forecasts of landfalling ARs and associated precipitation are sensitive to initial condition errors in and around the ARs while offshore. This sensitivity promoted the development of ensemble and adjoint based targeting strategies specific to AR conditions, which are used in concert with essential atmospheric structures to design observations to maximize impact. Motivated by early demonstrations of value, AR Recon observations are now officially called for in the U.S. National Winter Season Operations Plan. The program is led by the Center for Western Weather and Water Extremes (CW3E) in close collaboration with NOAA NCEP. The foundational observations within AR Recon are dropsondes, which provide atmospheric vertical profiles of temperature, moisture, winds, and pressure at targeted locations over the northeast Pacific. AR Recon also partners with the Scripps-based Lagrangian Drifter Laboratory, which runs the NOAA funded Global Drifter Program, to deploy drifting ocean buoys with surface pressure sensors to support the project’s forecast improvement objectives. Prototype real-time data streams for airborne radio occultation, an innovative remote sensing technique making use of all major GNSS satellite signals, are in active development. Targeted radiosonde releases are conducted by CW3E at up to four locations simultaneously in California after AR landfall, throughout the duration of the storm. Near real-time data denial experiments are carried out to examine the dropsonde impact on the NCEP GFS (global forecast system) forecast.

Water year 2023 was an exceptionally active year for AR Recon because of the high number of ARs that made landfall in California during the season. Based on demonstrated need in prior seasons, water year 2023 was the first time that AR Recon conducted missions before January. The early season saturation of soil moisture in a succession of events led to extensive flooding in California's Central Valley, and a state of emergency was declared in January. ARs continued to bring record breaking precipitation and damaging winds to the state. A large fraction of this season's ARs were sampled with at least one AR Recon aircraft.This presentation will cover the accomplishments of the AR Recon RAOP with a focus on results from data impact studies, program evolution culminating in the data collected during water year 2023, and future plans based on results to date.