NOUS41 KWBC 021750



Technical Implementation Notice 16-30

National Weather Service Headquarters Washington DC

150 PM EDT Tue Aug 2 2016


To:       Subscribers:

         -NOAA Weather Wire Service

         -Emergency Managers Weather Information Network


         Other NWS Partners, Users and Employees


From:    Tim McClung

         Portfolio Manager

         Office of Science and Technology Integration


Subject: Implementation of National Water Model

         Effective: August 16, 2016


Effective on or about Tuesday, August 16, 2016, beginning with

the 1200 Coordinated Universal Time (UTC) run, the National

Centers for Environmental Prediction (NCEP) will begin

operationally running the National Water Model (NWM).


The NWM is an hourly cycling uncoupled analysis and forecast

system that will provide streamflow for 2.7 million river

reaches and other hydrologic information on 1km and 250m grids. 

It will provide complementary hydrologic guidance at current NWS

river forecast locations and significantly expand guidance

coverage and type in underserved locations.


The NWM ingests forcing from a variety of sources including

Multi-Radar Multi-Sensor (MRMS) radar-gauge observed

precipitation data and High-Resolution Rapid Refresh (HRRR),

Rapid Refresh (RAP), Global Forecast System (GFS) and Climate

Forecast System (CFS) Numerical Weather Prediction (NWP)

forecast data.


USGS real-time streamflow observations are assimilated; all NWM

configurations benefit from the inclusion of 1,260 reservoirs. 

The core of the NWM system is the NCAR-supported community 

WRF-Hydro hydrologic model.  WRF-Hydro is configured to use the

NoahMP Land Surface Model (LSM) to simulate land surface

processes. Separate water routing modules perform diffusive wave

surface routing and saturated subsurface flow routing on a 250m

grid, and muskingum-cunge channel routing down NHDPlusV2 stream

reaches. River analyses and forecasts are provided across a

domain encompassing the CONUS and hydrologically-contributing

areas, while land surface output is available on a larger domain

that extends beyond the CONUS into Canada and Mexico (roughly

from latitude 19N to 58N). In addition, NWM forcing datasets

will also be provided on this domain at a resolution of 1km.


General Framework:


The NWM will be run in four configurations:

   -Analysis and assimilation 1 hour snapshot

   -Short-Range 15 hour deterministic forecast

   -Medium-Range 10 day deterministic forecast

   -Long-Range 30 day ensemble forecast


Analysis and Assimilation:


The Analysis and Assimilation configuration will cycle 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 15 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 does not exist. 

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 will produce

hourly deterministic forecasts of streamflow and hydrologic

states out to 15 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 once per

day, 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 (i.e., every 

6 hours) 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





All NWM output will be stored in NetCDF format in one of three

file types:

   -1km gridded NetCDF (land surface variables and forcing)

   -250m gridded NetCDF (runoff variables)

   -Point-type NetCDF (stream routing and reservoir variables)


The two gridded files cover a rectangular domain stretching

beyond the CONUS, roughly from 19N to 58N, while the point

netcdf files contain model output from the CONUS and

hydrologically contributing areas. 


End users will be able to view the output via the interactive

map viewer on the Office of Water Prediction (OWP) website:


Additionally, the full set of NWM output and a subset of forcing

files will be available on NOMADS and the NCEP FTP server at:


The following directory structure will be used:


NWM Model Forcing (fe=forcing engine, cyc=model cycle):





nwm.t${cyc} (### is 001-015)



nwm.t${cyc} (### is 001-240)


NWM Model Output (cyc=model cycle):







nwm.t${cyc} (### is


nwm.t${cyc} (### is 001-015)

nwm.t${cyc} (### is 001-


nwm.t${cyc} (### is




nwm.t${cyc} (### is


nwm.t${cyc} (### is 003-240)

nwm.t${cyc} (### is


nwm.t${cyc} (### is







nwm.t${cyc} (+ is 1-4,

### is 006-720)

nwm.t${cyc} (+ is 1-4, ###

is 024-720)

nwm.t${cyc} (+ is 1-4,

### is 006-720)


Due to storage space limitations, the latitude and longitude of

each output grid-box (for grid-type data) and point (for 

point-type data) are stored outside of the individual NWM NOMADS

NetCDF files, in files available at:


Scripts are available at this same location, which will append

this geospatial data to a user selected output file, enabling

viewing within common NetCDF visualization utilities.


A consistent parallel feed of NWM data is available on the NCEP

server via the following URL:


NCEP encourages all users to ensure their decoders are flexible

and are able to adequately handle changes in content order and

also any volume changes which may be forthcoming. These elements

may change with future NCEP model implementations. NCEP will

make every attempt to alert users to these changes prior to any



For more general information about the NWM, please see:


For questions regarding this implementation, please contact:


     Brian Cosgrove

     OWP/Analysis and Prediction Division

     Silver Spring, MD



For questions regarding the data flow aspects of these datasets, please contact:


     Carissa Klemmer

     NCEP/NCO Dataflow Team

     College Park, Maryland 20746



NWS National Technical Implementation Notices are online at: