NOUS41 KWBC 181603 AAB



Technical Implementation Notice 14-24, Amended

National Weather Service Headquarters Washington DC

1205 PM EDT Fri Jul 18 2014


To:        Subscribers:

           Family of Services

           NOAA Weather Wire Service

           Emergency Managers Weather Information Network


           Other NWS Partners, Users and Employees


From:      Tim McClung

           Science Plans Branch Chief

           Office of Science and Technology


Subject:   Amended: New North American Land Data Assimilation

           System (NLDAS):  Effective August 5, 2014


Amended to change the implementation date from July 29, 2014, to 

August 5, 2014


Effective on or about Tuesday, August 5, 2014, the National

Centers for Environmental Prediction (NCEP) will begin to run and

disseminate data from the North American Land Data Assimilation

System Version 2.0.0 (NLDAS-2).


NLDAS is a multi-model land modeling and assimilation system run

in an uncoupled mode on a common one-eighth degree grid covering

the Continental United States (CONUS) along with northern Mexico

and southern Canada, and driven by atmospheric forcing. 


NLDAS provides retrospective and real-time high-resolution water

and energy cycle products, such as surface fluxes, soil moisture,

snow cover, and runoff/streamflow, along with the near-surface

atmospheric and precipitation data sets used as forcings for the

NLDAS land models. These products support drought monitoring,

seasonal hydrological prediction, weather and climate

forecasting, model evaluation, and land-hydrology research within

these communities. 


NLDAS has become a mature system and is being implemented into

real-time National Centers for Environmental Prediction (NCEP)

operations in the near future. The retrospective component of

Phase 2 of NLDAS (NLDAS-2; Ek et al, 2011) was completed in 2008


Since then, NLSDA has continued in near real time. NLDAS-2 was

developed at the National Oceanic and Atmospheric Administration

NCEP Environmental Modeling Center (EMC) in collaboration with

its NOAA Climate Program Office (CPO) Climate Prediction Program

of the Americas (CPPA) partners. These partners include the

National Aeronautics and Space Administration/Goddard Space

Flight Center (NASA/GSFC), Princeton University, the University

of Washington (UW), the NWS Office of Hydrologic Development

(OHD), and the NCEP Climate Prediction Center (CPC). It can be

considered as the follow-on to Phase 1 of NLDAS (Mitchell et al,

2004), which was supported through the NOAA Office of Global

Programs (now CPO) GEWEX Americas Prediction Project (GAPP) and

the NASA Terrestrial Hydrology Program.


Ek, M. B., and co-authors, 2011:  North American Land Data

Assimilation System Phase 2 (NLDAS-2).  Development and

Applications, GEWEX News, May, 21(2), 6-7, 20


Mitchell, K. E., and co-authors, 2004:  The multi-institution

North American Land Data Assimilation System (NLDAS):  Utilizing

multiple GCIP products and partners in a continental distributed

hydrological modeling system.  J. Geophys. Res., 109, D07S90,



For references see NLDAS publications in NASA NLDAS-2 website


1.  NLDAS-2 data and their distribution:


NLDAS Version 2 generates hourly surface forcing at standard

model boundary layers (e.g., 2m air temperature and specific

humidity, 10 m wind speed, surface pressure, downward shortwave

and longwave radiation, precipitation) and the NCEP RCDAS lowest

model layer. NLDAS also provides hourly simulation for energy

fluxes (e.g., sensible heat flux, latent heat flux, ground heat

flux, net radiation etc.), water fluxes (e.g.,

evapotranspiration, total runoff/streamflow, precipitation,

etc.), and state variables (e.g., soil moisture, soil

temperature, snow water equivalent, land surface temperature,

snow cover, etc.) listed below from the four land surface models,

once per day for the 12 UTC cycle.


The NLDAS-2 output will be available in GRIB2 format on a 1/8th x

1/8th degree output grid. The NLDAS output will be disseminated

via the ftp/http server:


NLDAS produces the forcing files with a 3.5-day lag and the

output from the four LSMs with a 4-day lag. Therefore, NLDAS

output generated today will be available in directories dated 3

and 4 days ago. Output files and their contents include:


1.1  NLDAS-2 forcing:


NLDAS produces "a" and "b" forcing files.  The "a" files are the

primary NLDAS forcing files.  The "b" files are directly

downscaled from the NARR/RCDAS reanalysis at the lowest

prognostic model level with a spatial variation for diverse



File a: nldas.t12z.force-a.grb2f$HR, where HR = 00, 01,..., 23 2D

products include:

(1) TMP at 2 m: 2-m air temperature (K),

(2) SPFH at 2 m: Specific Humidity (kg/kg),

(3) PRES on the surface: surface pressure (pa),

(4) UGRD at 10 m: 10 m u component (m/s),

(5) VGRD at 10 m: 10 m v component (m/s),

(6) DLWRF on the surface: downscaled RCDAS downward longwave

radiation (W/m^2),

(7) FRAIN on surface: convection precipitation fraction to total

precipitation (--),

(8) CAPE:  Convective Available Potential Energy (J/kg),

(9) PEVAP Potential Evaporation (kg/m^2),

(10) APCPN: Gauge-based total precipitation (kg/m^2),

(11) DSWRF: Bias-corrected RCDAS Downward Short-Wave Radiation

Flux (W/m^2)


File b:   nldas.t12z.force-b.grb2$HR, where HR=00, 01,..., 23 2D

products include:

(1) DSWRF: downscaled RCDAS Downward Short-Wave Radiation Flux


(2) APCPN: Downscaled RCDAS Total precipitation [kg/m^2],

(3) ACPCP: Convective Precipitation [kg/m^2],

(4) ACOND: Aerodynamic conductance [m/s],

(5) TMP: The lowest model layer Temperature [K],

(6) SPFH: the lowest model layer Specific Humidity [kg/kg],

(7) PRES: The lowest model layer Pressure [Pa],

(8) UGRD: The lowest model layer U-Component of Wind [m/s],

(9) VGRD: The lowest model layer V-Component of Wind [m/s], and 

HGT: Geopotential Height [gpm].


1.2  Output from the Four Land Surface Models:


$model.t12z.grbf$HR, where model=Mosaic, Noah, SAC, and VIC;

HR=00, 01.,02,..., 23


Model outputs include hourly energy fluxes, water fluxes, and

states variables. For details, see the Model Output tab on the 



NASA NLDAS website:


Details are also in NLDAS-2 publications (Xia et al., 2012a). It

should be noted that soil moisture in SAC model is not for any

specific soil layer rather than six components of two reservoirs

(shallow upper and deeper lower). A post-process algorithm can be

used to generate soil moisture for a specific soil layer (Xia et

al., 2012a, Xia et al., 2014). Soil moisture and temperature for

VIC model are not for a specific soil layers for the second and

third soil layer as soil layers for these two layers vary from

grid cell to grid cell. Similar to the SAC model, a post-process

algorithm developed by Princeton University can be used to

generate soil moisture and temperature for a given soil layer

(Xia et al., 2012a).


1.3  Routed Streamflow from the Four Land Surface Models:


The River Routing Model developed by Lohmann et al. (2004) was

used to generate gridded streamflow over the CONUS. The results

from NLDAS-2 have been comprehensively evaluated using long-term

observed streamflow from 961 USGS basins (Xia et al., 2012b). The

output data include routed streamflow:


$model.t12z.STRM.grbf$HR, where model=Mosaic, Noah, SAC, and VIC;

HR=00, 01, 02,..., 23; STRM: routed streamflow (m^3/s)


2.  NLDAS-2 Operational Run:


A consistent parallel feed of data is currently available on the

NCEP server at:



Users please note that NLDAS-2 products are encoded in GRIB2

using a relatively-new GRIB template.  Users should download the

latest versions of wgrib2 and the other NCEP GRIB utilities to

use the NLDAS-2 output products.  Users can access the NCEP GRIB

utilities from this URL:


A website containing more information about GRIB2 can find at:


For questions regarding the scientific content of the NLDAS

system please contact:


Michael B. Ek


College Park, Maryland 20740




Youlong Xia


College Park, Maryland 20740



For questions regarding the dataflow aspects of these data sets

please contact:


Rebecca Cosgrove

NCEP/NCO Dataflow Team

College Park, Maryland 20740



NWS National Technical Implementation Notices are online at: