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The NWM is an hourly cycling uncoupled analysis and forecast system that provides streamflow for 2.7 million river reaches and other hydrologic information on 1km and 250m grids. It provides complementary hydrologic guidance at current NWS river forecast locations and significantly expand guidance coverage and type in underserved locations.
The NWM is run operationally in four configurations:
-Analysis and assimilation 1 hour snapshot
-Short-Range 18 hour deterministic forecast
-Medium-Range 10 day deterministic forecast
-Long-Range 30 day ensemble forecast
Analysis and Assimilation:
The Analysis and Assimilation configuration cycles hourly and produces a real-time snapshot of the current streamflow and general hydrologic states across the country. This configuration also produces the initialization for the 18 hour, 10 day and 30 day forecast simulations. Precipitation forcing data are drawn from the MRMS gauge-adjusted and radar-only observed precipitation products along with short-range RAP and HRRR forecasts in areas where MRMS radar coverage is poor. Short-range RAP and HRRR forecasts supply the other meteorological forcing variables. Real-time USGS streamflow observations are assimilated into this configuration.
Short Range Forecast:
The Short Range Forecast configuration cycles hourly, is forced with meteorological data from the HRRR and RAP, and produces hourly deterministic forecasts of streamflow and hydrologic states out to 18 hours. The model is initialized with a restart file from the Analysis and Assimilation configuration and does not cycle on its own states.
Medium Range Forecast:
The Medium Range Forecast configuration is executed four times per day at 00Z, 06Z, 12Z and 18Z, is forced with GFS model output, and extends out to 10 days. It produces 3-hourly deterministic output and is initialized with the restart file from the Analysis and Assimilation configuration.
Long Range Forecast:
The Long Range Forecast cycles 4 times per day at 00Z, 06Z, 12Z and 18Z and produces 30-day ensemble forecasts of streamflow, other hydrologic states and evapotranspiration. There are four ensemble members in each cycle of this forecast configuration, each forced with a different CFS forecast member. This configuration allows for a total of 16 ensemble members per day. It produces 6-hourly streamflow and daily land surface output, and, as with the other forecast configurations, is initialized with a common restart file from the Analysis and Assimilation configuration.
For more information please see the NWM Website