The NWM simulates the water cycle with mathematical representations of the different processes and how they fit together. This complex representation of physical processes such as snowmelt and infiltration and movement of water through the soil layers varies significantly with changing elevations, soils, vegetation types and a host of other variables. Additionally, extreme variability in precipitation over short distances and times can cause the response on rivers and streams to change very quickly.
Overall, the process is so complex that to simulate it with a mathematical model means that it needs a very high powered computer or supercomputer in order to run in the time frame needed to support decision makers when flooding is threatened. The NWM produces hydrologic guidance at a very fine spatial and temporal scale. It complements official NWS river forecasts at approximately locations across the CONUS and produces guidance at millions of other locations that do not have a traditional river forecast.
The NWM runs ten uncoupled analyses simulations of current conditions with look-back periods ranging from 28 hours to 3 hours. Additionally, the CONUS features medium-range and long-range forecasts which are each produced four times per day.
The NWM provides complementary hydrologic guidance at current National Weather Service NWS river forecast locations and significantly expands guidance coverage and type in underserved locations. All analysis and forecast configurations benefit from the inclusion of over 5, reservoirs, with the CONUS short- and medium-range forecasts ingesting RFC-supplied forecasts of reservoir outflow at several hundred locations. Additionally, aiding model assessment and informing model application, three new open-loop forecast configurations CONUS medium-range, Puerto Rico and Hawaii short-range are initialized with conditions from the open-loop analyses.
The Standard Analysis and Assimilation configuration cycles hourly and produces a real-time analysis of the current streamflow and other surface and near-surface hydrologic states across the contiguous United States CONUS. The exception is the 19Z Standard Analysis cycle which ingests initial conditions from the Extended Analysis below.
The Standard Analysis also produces restart files each hour which are used to initialize the short-, medium-, and long-range forecast simulations. This configuration initializes the Open Loop Medium-Range forecast. The Extended Analysis and Assimilation configuration cycles once per day and produces an analysis of the current streamflow and other surface and near-surface hydrologic states across the contiguous United States CONUS. This configuration also produces restart files which are used to initialize the 19Z Standard Analysis simulation.
This configuration initializes the 19Z Open Loop Analysis simulation. The Long-Range Analysis and Assimilation configuration cycles hourly and produces a real-time analysis of the current streamflow and other surface and near-surface hydrologic states across the contiguous United States CONUS , using higher quality precipitation data than is available to the Standard Analysis and Assimilation.
The Long-Range Analysis also produces restart files which are used to initialize the long-range forecast simulations. Information about the NHD also can be obtained in a series of associated tables. Forest Service, and additional partners initiated the production of the NHD at , scale or better.
Skip to main content. Search Search. National Hydrography. National Hydrography Dataset. NHDLine contains linear features not core to the network. Year Select Year Apply Filter. See the Examples folder for example usage. The model files themselves are in netCDF format and include streamflow for all rivers at a single time step, e.
All timestamps are in UTC time. A single model file includes data at a single timestamp for roughly 2. To extract data for just the rivers in your study area from a downloaded model result file, supply a list of identifiers for those rivers. This is useful for getting a snapshot of conditions at a given date and time across all rivers in your study area. If you want to save a subset of the data for your rivers for later use, supply an output filename.
If you have several files for a given forecast and want to combine them, supply a list of files. The HydroShare subpackage within pynwm provides access to HydroShare's recent archives of model results, their API for querying the archive, and services supporting their Viewer and File Explorer apps. In addition to accessing archived simulation results, you can also query for a streamflow time series directly from HydroShare without having to first download model result files.
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