NOUS41 KWBC 071140 AAD

Technical Implementation Notice 11-16, Amended
National Weather Service Headquarters Washington DC
740 AM EDT Fri Oct 7 2011

To:       Subscribers:
          -Family of Services
          -NOAA Weather Wire Service
          -Emergency Managers Weather Information Network
          Other NWS Partners, Users and Employees  

From:     Tim McClung
          Chief, Science Plans Branch
          Office of Science and Technology

Subject:  Amended: Implementation Date Delayed: Changes to
          the North American Mesoscale (NAM) Analysis and
          Forecast System: Effective October 18, 2011

Amended to schedule the implementation for Tuesday, October 18, 2011. Users are reminded that declaration of a Critical Weather Day (CWD) may result in the NAM being implemented on or around the October 18.

Effective on Tuesday, October 18, 2011, with the 1200 UTC cycle, the National Centers for Environmental Prediction (NCEP) will modify the NAM Analysis and Forecast System.

These changes include:

-Introducing a new modeling framework
-Installing a major upgrade to the prediction model
-Modifying the data analysis and assimilation system
-Adding to existing NAM products
-Adding new higher-resolution nests within the NAM including a very high-resolution but small domain to support fire weather and Incident Meteorologist (IMET) interests 

Details on the various changes are provided below, along with a notice about possible changes to product generation time.  

Model Upgrades  

NCEP will introduce the use of the new NOAA Environmental Modeling System (NEMS), which is based on the tenets put forth by the Earth System Modeling Framework to which NOAA has subscribed. Eventually all of NCEP’s major modeling will be performed within NEMS. This NAM upgrade represents the first implementation of NEMS and a major step in the evolution of NCEP’s modeling suite.

The prediction model used in the NAM run will go from being the strictly regional Nonhydrostatic Mesoscale Model (NMM) to a new extended capability version now known as Nonhydrostatic Multiscale Model on B-grid (NMMB), which can be run either regionally or globally with or without embedded nests.  This NEMS-NMMB also will serve as the prediction model running in the NAM Data Assimilation System (NDAS). Model changes/enhancements in the NEMS-NMMB will include the following:  

a) Native horizontal grid is an Arakawa staggered B-grid
   (rotated 45 deg. from the Arakawa E-grid in the WRF-NMM NAM) b) New more conservative Eulerian advection scheme for passive  
   tracers like water vapor condensate fields 
c) Generalized vertical coordinate
d) Modified vertical level distribution with more layers in the
   stratosphere (14 layers above 200 mb instead of 7 in the
   current operational NAM)
e) Boundary condition treatment changed to specify 5 boundary
   rows instead of 1
f) Microphysics changes to produce higher peak reflectivities
   above 45 dBZ, with higher peak surface rainfall rates in the
   high-resolution nests and more realistic grid-scale cloud
   fractions from cold, high cirru
g) Change from USGS to MODIS_IGBP land-use definitions
h) Enhanced diffusion for specific humidity and cloud water
i) Run 5 high-resolution nested domains inside the 12km NAM
   every cycle.  These nests will run with greatly reduced
   convective triggering, which improved quantitative
   precipitation forecast (QPF) bias compared to using
   explicit convection

All model changes will also be applied to the Downscaled GFS by NAM Extension (DGEX) forecast system.

NDAS Changes:


a) Initial first guess at T-12hr will reflect relocation of
   tropical cyclones
b) Will use 1/12 degree high resolution real-time sea surface
   temperature (RTG_SST_HR) analysis instead of the 1/2 degree
   real-time SST analysis.
c) Will update 2 m temperature and moisture and 10 m wind with
   portion of first layer correction  

Changes to the Gridscale Statistical Interpolation (GSI) analysis: 

a) New faster version of the GSI code with new observation error 
   estimates, retuned background error covariances for NMMB and
   upgraded radiative transfer (CRTM v2.0.2)
b) Assimilation of new observations: ACARS humidity, Windsat and
   ASCAT (superob'ed Scatterometer winds over oceans), HIRS
   radiances from NOAA-19, AMSU-A radiances from NOAA-19
   and AQUA, IASI radiances from METOP, GPS radio occultation
   refractivity (COSMIC), RASS virtual temperatures, MAP
   (boundary layer profiler) winds and MESONET surface
   pressure/temperature/ humidity (winds already included)

c) Use dynamic reject list for surface mesonet data from the

   NCEP Real-time Mesoscale Analysis (RTMA)

Changes to the NAM post-processing code:

a) The height and wind speed at the maximum wind level will be

   computed by assuming the wind speed varies quadratically in

   height in the neighborhood of the maximum wind level with the

   search being capped at 100mb. The previous algorithm defines

   maximum wind level as the level with the maximum wind speed

   among all the model levels.

b) The static Tropopause level will be obtained by finding the

   lowest level that has a temperature lapse rate of less than

   2K/km over a 2km depth above it. If no such level is found

   below 50 mb, the Tropopause is set to 50 mb. The previous

   algorithm defines the Tropopause by finding the lowest level 

   with a mean temperature lapse rate of 2K/Km over three

   model layers.

c) All Convective Available Potential Energy (CAPE), Convective

   Inhibition (CIN), and Lifted Index (LI) variables in the NAM

   output will be computed using virtual temperature instead of

   sensible temperature.  See the NWS Public Information

   Statement issued January 12, 2011, for more details on

   this change.  

Users should be aware that this NAM upgrade will impact all downstream models and systems using the NAM or NDAS as input. 

Output Product Changes:   

New NAM Nest runs, including placeable Fire Weather Nest. Five new high-resolution nested domains will run inside the
12 km NAM every cycle:

a) CONUS (4 km resolution, 0-60 h)

b) Alaska (6 km resolution, 0-60 h)

c) Hawaii and Puerto Rico (both 3 km resolution, 0-60 h)

d) Placeable nest will run to 36-h inside either the CONUS nest

   (at 1.33 km resolution) or Alaska nest (at 1.5 km

   resolution). This nest is primarily for Fire Weather/IMET-DHS

   Support (FWIS). The locations of this domain for each of the

   4 NAM cycles will be determined via a daily coordination call

   conducted by the NCEP Senior Duty Meteorologist.  

A sample display of the domain coverage of these new nests is available at:

Output grids from the NAM nest runs will be available on the NCEP ftp server immediately and on the NCEP NOMADS server in the future. The fields contained in the NAM nest output grids are listed at:

Changes to parent NAM gridded output on the NCEP ftp server and the NWS ftp server:

a) In all NAM grids that contain roughness length, the precision

   was changed to provide better decimal scaling because many

   land-use types have roughness length much less than 1.

b) Surface slope type was dropped from all NAM output grids as

   it is no longer used in the model land-surface physics

c) Time-averaged surface momentum flux record is being removed

   from all NAM GRIB files as it is not defined and thus had

   been set to zero in the current operational NAM 

d) New output fields:

   - Clear Air Turbulence (Ellrod Index), every 25 mb from

     150-525 mb, and Inflight Icing every 25 mb from 300-600 mb,

     every 50 mb from 650-950 mb, and 725 mb; added to grid

     #221 (32 km grid over North America)

   - 80 km above ground level pressure, temperature, wind, and

     specific humidity; added to grid #221 (32 km grid over

     North America), grid #218 (12 km grid over CONUS, pressure

     file only) and grid #242 (11.25 km grid over Alaska,

     pressure file only).

   - Hourly max and min surface fields (10-meter wind, 2-meter

     temperature, 2-meter relative humidity);  added to grid

     #221 (32 km grid over North America), grid #218 (12 km

     grid over CONUS, both versions) and grid #242 (11.25 km

     grid over Alaska).

   - Haines Index: Added to grid #218 (12 km grid over CONUS,

     both versions) and grid #242 (11.25 km grid over Alaska,  

     both versions)

   - Ventilation Rate: Added to grid #218 (12 km grid over

     CONUS) and grid #242 (11.25 km grid over Alaska).

   - Rain and snow on lowest model level: added to grid #218

     surface file "awip12"

   - Thunder parameter (called lightning in GRIB): added to

     both grid #218 files


e) All NAM output files on the native horizontal staggered

   E-grid of the current operational WRF-NMM will be on the

   staggered B-grid of the NEMS-NMMB. The current native grid

   files with names "egrd3d," "edgawp," and "egrdsf" will be

   removed from the NCEP FTP server and replaced with files with

   names "bgrd3d", "bgdawp," and "bgrdsf," respectively. Users

   who process current NAM native GRIB files with e-grid

   staggering will need to modify their software to process

   b-grid staggering.


f) To provide the critical variables used at Weather Forecast

   Offices to generate their National Digital Forecast Database

   (NDFD) forecast grids, NCEP will begin to populate the

   current NAM Downscaled Numerical Guidance (DNG - a small set

   of 2-dimensional fields) in the 0-60 hr range from the new

   high-resolution NAM nested fields instead of the parent NAM

   12 km fields. The NAM DNG grids are currently distributed to

   CONUS, Alaska, Hawaii and Puerto Rico over the AWIPS

   SBN/NOAAPORT.  In response to requests from the NWS Regions,

   NCEP also plans on producing a CONUS 2.5km NAM-DNG for the

   0-60 hr in addition to the current CONUS 5 km version. 

   A separate TIN will announce the addition of those 2.5 km

   grids to NOAAPORT. 


g) Several users have noted differences in the precision of the

   accumulated precipitation at different forecast projections.

   With this upgrade, the precision for all forecast hours will

   be standardized.

Product Delivery Time Change:

NCEP anticipates that output delivery times after the NAM upgrade will differ slightly throughout the run compared to the current operational NAM products. The precise amounts still need to come out of the final pre-implementation testing by NCEP Central Operations, but the following is the worst case scenario. When the CONUS Fire Weather nest is run during the first 36 hours of the forecast, product delivery will lag the current delivery by ~13 seconds each forecast hour such that
36 hour guidance will be 468 seconds or 7.8 minutes later than at present. Following the 36 hour point of the forecast, NWS will recover delivery time at roughly 10 seconds each forecast hour such that delivery of the 84 hr guidance will be at the same time as it is delivered today, which is 10 minutes earlier than its target.  As an example, for 0000UTC run, the following delivery time differences would be expected, with current time in parentheses: 

12hr PRODUCTS at 01:52:52 (01:50:16)

24hr PRODUCTS at 02:05:26 (02:00:14)

36hr PRODUCTS at 02:17:49 (02:10:01)

48hr PRODUCTS at 02:25:47 (02:19:59)

60hr PRODUCTS at 02:34:04 (02:30:16)

72hr PRODUCTS at 02:40:23 (02:38:35)

84hr PRODUCTS at 02:50:23 (02:50:35)   

The target delivery for 84 hr guidance is 3:00:00.

When the fire weather nest is over Alaska, product delivery will lag the current delivery by ~5 seconds each forecast hour such that 36 hour guidance will be 180 seconds or 3 minutes later than at present.

For a detailed description of this NAM and NDAS upgrade, including verification statistics, please see:

For more general information about the NAM and NDAS, please see:

A consistent parallel feed of data will become available on the NCEP server once the model is running in parallel on the NCEP Central Computing System by late May.  The parallel data will be available via the following URLs:

NCEP has tried to anticipate all filename and product content changes associated with this implementation, but if we discover additional changes during the course of the testing, we will send an amended version of this TIN with that information as soon as possible.

NCEP urges all users to ensure their decoders can handle changes in content order, changes in the scaling factor component within the product definition section (PDS) of the GRIB files, changes to the GRIB Bit Map Section (BMS), and volume changes. These elements may change with future NCEP model implementations. NCEP will make every attempt to alert users to these changes before implementation.

For questions regarding these changes, please contact:

      Geoff DiMego

      NCEP/Mesoscale Modeling Branch

      Camp Springs, Maryland

      301-763-8000 X 7221


      Eric Rogers

      NCEP/Mesoscale Modeling Branch

      Camp Springs, Maryland

      301-763-8000 X 7227


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


     Rebecca Cosgrove

     NCEP/NCO Dataflow Team

     Camp Springs, Maryland 20746

     301-763-8000 X 7198


NWS National Technical Implementation Notices are online at: