NOUS41 KWBC 271800 AAA



Technical Implementation Notice 16-41 Updated

National Weather Service Headquarters Silver Spring, MD

200 PM EST Fri Jan 27 2017


To:       Subscribers:

          -NOAA Weather Wire Service

          -Emergency Managers Weather Information Network


          Other NWS Partners, Users and Employees


From:     Dave Myrick

          NWS Office of Science and Technology Integration


Subject:  Updated: Upgrade to the North American Mesoscale (NAM) 

          Forecast System and Discontinuation of Downscaled GFS

          by NAM Extension (DGEX) Forecast System Effective

          on a date to be determined.


Amended to: 

* Update product removals from both web services and NOAAPORT

* Include the downstream removal of GLW NAM winds

* Include GRIB packing changes

* Include variable changes

* Amend the implementation date


Effective on or about a date to be determine, the National

Centers for Environmental Prediction (NCEP) is proposing to

implement Version 4 of North American Mesoscale (NAM) and

discontinue the Downscaled GFS by NAM Extension (DGEX) Forecast



* Discontinuation of all DGEX model output

* Removal of legacy NAM products on NOAAPORT and NCEP/NWS


* Resolution changes for NAM nests

* NAM Data Assimilation System (NDAS) major changes

* Model Changes - convection, microphysics, land-surface

upgrades; frequency of physics calls increased




1) Resolution changes to the CONUS (from 4 to 3 km), Alaska

(from 6 to 3 km), and CONUS fire weather (from 1.333 to 1.5 km)


2) More frequent calls of physics (now every 2nd time step for

all domains); change frequency of radiation updates for the NAM

12 km parent domain from hourly to every 20 minutes

3) Advect specific humidity every dynamics time step

4) Changes to Betts-Miller-Janjic convective scheme to improve

12 km parent QPF bias, especially during the cool season

5) Updated Ferrier-Aligo microphysics to improve stratiform

precipitation, better anvil reflectivity, reduce areas of

light/noisy reflectivity over oceans

6) Improved effect of frozen soil on transpiration and soil

evaporation, leads to reduced cold/moist bias during cool season

7) Radiation/microphysics changes to reduce incoming surface

shortwave radiation; reduced warm-season 2-m temperature bias




1) Replace 12-h NAM Data Assimilation System (NDAS) with 3-h

analysis updates for the 12 km parent domain with a 6-h data

assimilation cycle with hourly analysis updates for the 12 km

parent and the 3 km CONUS/Alaska nests. The Hawaii/Puerto

Rico/Fire weather nests will be initialized from the 12-km first

guess at the end of 6-h assimilation cycle.

2) Use lightning data (from NLDN and ENL networks) and radar

reflectivity-derived temperature tendencies in the diabatic

digital filter initialization.

3) Add execution of the diabatic digital filter initialization

prior to the NAM forecast (was only run during NDAS in current

ops NAM version 3).

4) Assimilate new observation types:

  - Aircraft data: Aeromexico, ADS-C, Air-Wisconsin

  - New satellite radiance data: NOAA NPP (ATMS, CRIS),



  - New GPS Radio Occultation data: METOP-B 3 (subtype)

  - New satellite winds: Himawari-B, METEOSAT-7, 10 Imager WV





1) Reinstate use of 557th Weather Wing (formerly AFWA) 23 km

snow depth analysis using envelope adjustment

2) Use a new climatology of fresh water lake temperatures

(FLAKE) for inland water bodies not resolved by the 1/12th

degree RTG_SST_HR analysis in the CONUS, Alaska, and Fire

weather nests

3) Reduce terrain smoothing in all NAM nest domains

3) Use NESDIS burned area data (30-day and 2-day average) in the

fire weather nest; greenness fraction and albedo are adjusted

based on the 30-day average, top-layer soil moisture based on

the 2-day average

4) Perform Tropical cyclone relocation for the 12 km parent

domain at the start of the 6-h catchup cycle and for the NAM

forecast first guess.




Files below can be found on the following NCEP services:


1) The output grid for nests will change:

CONUS nest: change from grid #227 to the same output grid as the

HRRR. See link below for difference:



      Where CC is cycle and FF is forecast hour 00-60

Alaska nest: change from the 6 km NDFD grid to the 3 km NDFD




2) All NAM nests grids will be output hourly from 0-60 hour; in

the current ops NAMv3 they were output hourly from 0-36h and 3-h

from 39-60 hour.


3) Added 1-h maximum precipitation rate (PRATE) and frozen

precipitation rate (SRWEQ) to the following grids:





    Where CC is cycle and FF is forecast hour and ## is either:

alaska, conus, prico, hawaii, firewx


4) Add a new visibility field based on the GSD algorithm to the

following output grids (this field is labeled with vertical

level=cloud top (VIS))










  Where CC is the cycle time and FF is the forecast hour


5) Change ceiling height (HGT) in the NAMv4 from height above

ground level to height above mean sea level for all output files


6) Rename the NAM 12km CONUS grid #218 file:

  nam.tCCz.awphysFF.grb2.tm00 -> nam.tCCz.awphysFF.tm00.grib2


7) Rename the 0.108 deg lat/lon Caribbean grid:

  nam.tCCz.afwacaFF.grb2.tm00 -> nam.tCCz.afwacaFF.tm00.grib2


8) Rename the 0.108 deg lat/lon Hawaii grid:

  nam.tCCz.afwahiFF.grb2.tm00 -> nam.tCCz.afwahiFF.tm00.grib2


9) The current NAM 12km Alaska grid #242 file contains both

surface and upper level data. In NAMv4 it is being renamed and

will contain mostly pressure level data:

  nam.tCCz.awak3dFF.grb2.tm00 -> nam.tCCz.awak3dFF.tm00.grib2


A second grid #242 file called is being added to the server,

this contains mostly surface fields that will not be in the new

awak3d file:



10) The GRIB2 labeling for 0-6 km integrated vertical u- and v-

components of the wind shear is changing from 6000-0 m above

ground to 0-6000 m above ground). This field is output in the

following grids:







11) The GRIB2 sigma value label for 0.33-0.67 sigma RH and 0.67-

1.00 sigma RH will change to 0.33-0.66 sigma RH and 0.66-1.00

sigma RH in the following grids:




12) The GRIB2 sigma level label for 0.7848 sigma temperature and

0.8967 sigma temperature will change to 0.78483 sigma

temperature and 0.89671 sigma temperature for the following






13)  With the NAM Alaska nest horizontal grid resolution

changing from 6 km to 3 km, it will no longer run with

convective parameterization. Therefore the following convective-

type fields will no longer be output for the Alaska nest:

  Accumulated convective precipitation

  Convective precipitation rate

  Convective cloud top/bottom pressure

  Deep convective cloud top/bottom pressure

  Shallow convective cloud top/bottom pressure

  Total convective cloud cover

  Deep convective heating rate


14) The total snow water equivalent on the ground will be added

to the file:



15) The GRIB2 processing for the NAM nests has been streamlined

so that all 6 NAM nests will output the same variables. Thus,

the following fields that are now only available from the NAM

CONUS nest will also be output from the Alaska, Hawaii, Puerto

Rico, and fire weather nests:

  80 meter above ground pressure, specific humidity,

temperature, and wind

  0-6 km integrated vertical u- and v-components of the wind shear

  Vertically-integrated liquid water

As part of the streamlining of the GRIB2 processing for the NAM

nests, the following variables will be removed from the output

grid for the NAM Fire Weather nest:

  Dew point temperature on pressure levels except for 300, 400,

500, 700, 850, 925, and 1000mb

  Dew point temperature at the 1st and 2nd model levels above


  Absolute vorticity at 200 and 300mb levels

  Vertical velocity, relative humidity, and specific humidity at

2, 5, 7, 70mb levels

  Turbulent kinetic energy at 2, 5, 7, 10, 20mb levels

  Cloud ice, cloud water, rain, and snow mixing ratio and rime

factor at 2, 5, 10, 20, 70mb levels, and on the 2nd model level

above ground

  Grid-point latitude and longitude

  PBL Regime

  1-h average non-convective cloud cover

  Equivalent radar reflectivity factor for snow and rain

  1-h average total cloud cover

  Height, pressure, temperature, and reflectivity on the 2nd

model level above ground


16) NAMv4 output files on the NCEP/NWS web servers will be

written as GRIB2 format from the post-processing, instead of

first being written out in GRIB1 format and converted to GRIB2.

The GRIB2 compression type for each NAM domain will be as


  JPEG2000: Hawaii, Puerto Rico and Fire Weather nests

  Complex packing with 2nd order spatial differencing: CONUS

nest, Alaska nest and all output from 12km NAM parent domain


Variables in those grids created with GRIB2 complex compression

may occasionally contain invalid negative numbers.


Users may see some differences with the encoding and are

encouraged to upgrade their software to handle this. Please see

the links below for upgraded code:


17) The number of days archived on the NCEP web services will be

changed from 28 days to 7 days.


18) Based on feedback from PNS 16-43, remove NAM-driven Great

Lakes Wave (GLW) model, on this date, the following products

will be removed from /com/wave/prod/glw.YYYYMMDD/:




  Several bulletins provided within glw.tCCz.bull_tar

  Several bulletins provided within glw.tCCz.cbull_tar

  Several bulletins provided within glw.tCCz.csbull_tar

  Several bulletins provided within directory bulls.tCCz

Where CC is cycle at 00, 06, 12 and 18Z




NCEP solicited public feedback through PNS 16-34 NAM Removals.

After balancing user comments with the code management of the

production suite the following changes will be made:


Files below can be found on the following

NCEP servers via


Or NWS servers via


1) NAM Products listed will be discontinued from all NCEP web







  tiles.tCCz directory

    NOTE: Users who wish to obtain a subset of NAM grids can

generate then directly using the grid sub setting option on the

NCEP NOMADS server at (click on

"grib filter" option)



    NOTE: Users can replace these with the 90 km North American

polar stereographic grid #104: nam.tCCz.grbgrdFF.tm00.grib2



    NOTE:  Users should instead be using the higher resolution

2.5/3km NAM DNG products


2) The following will be removed from the NWS servers and can

instead by found on the NCEP servers












NOTE: Users can access these exact data sets on the NCEP servers

as direct grib output or by using NOMADS grib filter and are

encouraged to transition to the NCEP servers at any time. Please

reference this page for file name changes:


3) The ndas.YYYYMMDD directories on the NCEP servers will be

discontinued. All grids and BUFR observation files from the

NAMv4 6-h assimilation cycle will be written into the

nam.YYYYMMDD directory. Since the 12-h NDAS will be replaced by

a 6-h data assimilation cycle with hourly analyses, the grid

#212 files from the current NDAS, for example:


2 will be replaced by:


where YYYYMMDD is the cycle date, CC the cycle time


4) All DGEX model output from the NCEP servers under

dgex/prod/dgex.YYYYMMDD will be discontinued. The DGEX model

will no longer be run within the NCEP model suite.

  Where YYYYMMDD is year, month, day


5) Remove the GRIB1 NAM grid 215 products under directory on the NWS web servers.




NCEP solicited public feedback through PNS 16-34 NAM Removals,

after balancing user comments with the code management of the

production suite the following changes will be made:


1) All 00z and 12z cycle NAM FAX charts will be removed

Description                  WMO Headers

00 Hour 200MB Isobar/Temp     QHUA17 KWBC

00 Hour 500MB Isobar/Temp     QHTA11 KWBC

00 Hour 700MB Isobar/Temp     QHTA07 KWBC

00 Hour 850MB Isobar/Temp     QHUA04 KWBC

Analysis 300MB Isobar         QHUA15 KWBC

UPA                           PYMA[357]0 KWBC

UPA                           PYMA[28]5 KWBC

This legacy code can no longer be supported on the next

generation supercomputer. If users are interested in the code to

create the charts please contact EMC below. NCEP will also

investigate the possibility of the MAG creating replica charts.


See the link below for the exact WMO headers for items 2-4:


1. Removal of the lower resolution only for: NAM NDFD 5km CONUS

(grid 197) and 6km Alaska grids (grid 198)

2. Removal of grid 217, 22 km Alaska region Polar Stereographic

3. Removal of grid 215, 20km Regional CONUS

4. Removal of all DGEX products



A consistent parallel feed of data is available on the NCEP

server via the following URLs:


For more general information about the NAM, please see:


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, 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.


Any questions, comments or requests regarding this

implementation should be directed to the contacts below. We will

review any feedback and decide whether to proceed.


For questions regarding the science aspects, please contact:


Eric Rogers

NCEP/EMC/Mesoscale Modeling Branch

College Park, MD



For questions regarding the data flow aspects of these datasets,

please contact:


Carissa Klemmer

NCEP/NCO Dataflow Team Lead

College Park, Maryland 20746



NWS National Technical Implementation Notices are online at: