NOAA’s National Water Model: A Dynamically Evolving Operational Hydrologic Forecasting Framework

In National Weather Service (NWS) operations since August of 2016, the National Water Model (NWM) produces 24x7 guidance on streamflow, soil moisture, snowpack and other hydrologic components. This guidance supports the operational activities of NWS River Forecast Centers, the Federal Emergency Management Agency and other government entities, along with research and commercial sectors. Upgrades to the modeling system have occurred on a rapid basis--with three since 2016--under a partnership between the NWS Office of Water Prediction (OWP), the National Center for Atmospheric Research and the National Centers for Environmental Prediction. Based on the community WRF-Hydro software architecture, the system is underpinned by a network of 2.7 million vector-type river reaches for river routing, a 1km land surface grid for land surface modeling, and a 250m grid for surface and subsurface routing of runoff. This latest operational version builds on prior capabilities to provide improved accuracy and first-time ensemble forecast guidance. Additionally, the NWM’s expansion to Hawaii marks the first ever provision of operational streamflow guidance to this island domain.

The NWM will next be upgraded in late 2020 to 2021. This significant upgrade to V2.1 will include the assimilation of reservoir outflow data which will greatly improve the accuracy of downstream forecasts. Domain expansion will continue via the inclusion of the Great Lakes drainage area, along with Puerto Rico and the US Virgin Islands. Additionally, calibration will be improved via the use forcings from the new Analysis of Record for Calibration. Improving upon the existing 25-year NWM retrospective, this same forcing dataset will be used to underpin a new 40-year retrospective simulation.

Beyond V2.1, upgrades will continue to support a variety of additional activities within the NWS and broader hydrologic community. These include a model extension to simulate combined impact of freshwater and coastal flooding, a shallow groundwater model, and an improved collaborative development infrastructure.

This presentation will provide an overview of these recent and planned NWM upgrades, along with updates on community development and the other hydrologic activity areas.