Observations of Landfalling Atmospheric Rivers in Northern California During Early 2017: Description and Preliminary Results from the FIRO-2017 Field Campaign

Forecast Informed Reservoir Operations (FIRO) is a proposed management strategy that uses data from state of the art watershed monitoring and weather and water forecasting to support water management operations, with the goals of improving water supply reliability, enhancing flood risk mitigation capacity, and supporting recovery of endangered salmon. An essential part of FIRO is to understand and better predict Atmospheric Rivers (ARs), which provide ~50% of the annual precipitation, and cause most of the heavy rain and flood events in the Russian River region studied here.

To support this effort, the “FIRO-2017 field campaign” was held during January-March 2017 in the Russian River Watershed with the goal of documenting the impacts of local terrain on AR characteristics as they penetrate inland from the coast to the upper reaches of the Russian River watershed, and to form a unique database for model verification. The deployment capitalized on and extended the well-established NOAA HMT observing network already in place. Two field sites were equipped with Vaisala radiosonde systems, MicroRain Radars (MRRs), optical disdrometers, surface meteorology, and GPS-met systems were operated by the Center for Western Weather and Water Extremes (CW3E) with support from the US Army Corps of Engineers. One site was at the coast (Bodega Bay, which is also the site of an Atmospheric River Observatory (ARO) that is provided by NOAA and the California Department of Water Resources) and the other was an inland couplet (Ukiah and Potter Valley, near Lake Mendocino).

The 2017 water year has been among the wettest recorded in California. During the January-March 2017 period, the coastal/inland pair of radiosonde systems captured 13 storms with maximum IVT values nearing 1200 kg/m/s. During this campaign 275 radiosondes were launched, and data were continuously recorded by the MRRs and other ground instrumentation. Radiosonde profiles were provided to local NWS offices in near real time. This presentation will provide an overview of the field campaign as well as preliminary results. These will include a comparison of the ARO-observed bulk upslope water vapor flux, which is a proxy for vertically integrated vapor transport (IVT), to direct measurements of IVT from the radiosondes. The correlation of each of these measurements with precipitation measured in the nearby coastal mountains will also be presented.