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NOUS41 KWBC 181603

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:


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