Atmospheric River Reconnaissance

The Atmospheric River Reconnaissance (AR Recon) project is exploring use of dropsonde measurements in and around atmospheric rivers (AR) over the northeast Pacific Ocean to improve the prediction of landfalling ARs on the U.S. West Coast, including their associated precipitation and streamflow. Independent studies have identified initial condition errors in and around ARs offshore at 1-3 days lead time as the leading source of model forecast errors in landfalling ARs. In addition, uncertainties in a cold-air trough, with associated relative and potential vorticity anomalies north of the AR appears to be a second key source of initial condition error that can contribute to forecast busts. These busts are often associated with the development of a mesoscale frontal wave, the details of which determine when and where an AR may stall on or near the coast. It is hypothesized that the combination of initial condition errors associated with the AR and the cold-air system are a leading cause of errors in mesoscale frontal wave development and AR landfall.

AR Recon brings together scientists, forecasters, numerical weather prediction centers, and water management agencies to explore how to improve upon AR landfall position errors, which average hundreds of km at 1-3 days lead time. Data collection is co-led by the Center for Western Weather and Water Extremes (CW3E; cw3e.ucsd.edu) at Scripps Institution of Oceanography and NCEP’s Environmental Modeling Center, using aircraft and crews from the U.S. Air Force and NOAA, while identification of objective targets using a moist adjoint method is led by the Naval Research Laboratory. New forecast tools developed at CW3E with Plymouth State University (PSU) and other partners provide key information for flight planning. NOAA’s National Weather Service, PSU, NCAR, ECMWF and CW3E led the forecasting. To date, AR Recon missions have been flown in 2016 and 2018, and more are proposed for 2019. The 2018 campaign included observations of 6 AR events using up to 3 aircraft per event during January and February, and relied upon team of scientists from multiple academic institutions, government agencies and modeling centers to provide event forecast briefings and perform pre-flight planning. Collectively, these campaigns represent a novel collaborative effort between scientists and stakeholders to support improved forecasting of high-impact weather in the Western U.S. during winter through enhanced observation of ARs ahead of landfall.

The development of methodologies to effectively assimilate AR Recon observations into global and regional forecast models, and analysis of the impact of the data on those simulations, are underway following principles laid out by the Steering Committee on AR Recon Modeling and Data Assimilation. Steering committee membership includes leaders from the Scripps Institution of Oceanography, the National Center for Environmental Prediction, the Naval Research Laboratory, National Center for Atmospheric Research, the European Center for Medium-Range Weather Forecasting. It is envisioned that AR Recon will become part of the Nation’s winter weather operations in the coming years. This federal investment to support observational requirements is expected to result in vastly improved outcomes for water management and emergency preparedness in the West.