The National Water Model (NWM) is a water forecasting model operated by the National Water Center (NWC) of the NOAA National Weather Service. The NWM continually forecasts flows on 2.7 million stream reaches covering 3.2 million miles of streams and rivers in the continental United States [1]. It operates as part of the national weather forecasting system, with inputs from NOAA numerical weather prediction models, and from weather and water conditions observed through the US Geological Survey's National Water Information System. Reference materials for the computational framework behind NWM is published by NCAR [9] [10].

The NWC generates NWM streamflow forecasts for the continental US (CONUS) with multiple forecast horizons and time steps. Due to the output file sizes, these are normally not available for download more than a couple days at a time [2]. However, for a time a 40-day rolling window of these forecasts was maintained by HydroShare at RENCI [3], and a complete retrospective (August 2016 to the present) of the NWM Analysis & Assimilation outputs is maintained as well (contact help@cuahsi.org for access).

An archive of all NWM forecasts for the period Aug 18 to Sept 10, 2017 has been compiled at RENCI [4] [5], available as netCDF (.nc) files totaling 8TB. These can be browsed, subsetted, visualized, and downloaded (see [6] [7] [8]). In addition to these output files, we have uploaded to this HydroShare resource the input parameter files needed to re-run the NWM for the Harvey period, or for any time period covered by NWM v1.1 and 1.2 (August 2016 to this publication date in August 2018). These parameter files are also made available at [1].

See README for further details and usage guidance. Please see NOAA contacts listed on [1] for questions about the NWM data contents, structure and formats. Contact help@cuahsi.org if any questions about HydroShare-based tools and data access.

References
[1] Overview of the NWM framework and output files [http://water.noaa.gov/about/nwm]
[2] Free access to all National Water Model output for the most recent two days [http://water.noaa.gov/about/nwm - scroll down to links under "Downloading Output"]
[3] NWM outputs for rolling 40-day window, maintained by HydroShare [link is no longer available]
[4] Archived Harvey NWM outputs via RENCI THREDDS server [http://thredds.hydroshare.org/thredds/catalog/nwm/harvey/catalog.html]
[5] RENCI is an Institute at the University of North Carolina at Chapel Hill
[6] Live map for National Water Model forecasts [http://water.noaa.gov/map]
[7] NWM Forecast Viewer app [no longer available]
[8] CUAHSI JupyterHub example scripts for subsetting NWM output files [https://hydroshare.org/resource/3db192783bcb4599bab36d43fc3413db/]
[9] WRF-Hydro Overview [https://ral.ucar.edu/projects/wrf_hydro/overview]
[10] WRF-Hydro User Guide 2015 [https://ral.ucar.edu/sites/default/files/public/images/project/WRF_Hydro_User_Guide_v3.0.pdf]