Greetings,

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On June 13, 2006 starting with the 12 UTC model run, NCEP will replace the forecast model used in its North American Mesoscale (NAM) time slot.  Currently the the Eta forecast model is used for the NAM, but on this date it will be replaced with the Non-hydrostatic Mesoscale Model (NMM) in the WRF framework  The WRF/NMM with continue to run over the same domain and same horizontal resolution (12 km) as the Eta and its output will be available at the same time.  There will be some minor addition of products to the NAM output on the NCEP and NWS ftp servers, however products being disseminated over NOAAPORT will be unaffected by this upgrade.  There will be no name changes of files on FTP servers associated with this upgrade.

Specifics on the differences between the Eta and WRF/NMM systems are as follows:

1.  Model Changes
- Replace Eta prediction model with WRF version of the Non-hydrostatic Meso Model (WRF-NMM)
- Extended model top pressure from 25 mb to 2 mb
- Replace Eta step-mountain vertical coordinate with NMM hybrid sigma-pressure vertical coordinate
- Refined/retuned numerous aspects of the Eta model physics for use in the NMM

2.  Analysis Changes
- Replace Eta 3DVAR analysis system with the new unified GSI analysis system that has been adapted for application to the WRF-NMM
- Replace NEXRAD Level II.5 data in Eta 3DVAR with NEXRAD Level II radial wind data in GSI
- GSI uses background errors based on WRF-NMM forecasts; Eta 3DVAR used background errors based on GFS forecasts
- Use of dynamically retuned observational errors

3.  Data Assimilation Changes
- Implement direct use of observed precipitation analysis values in the Land-surface physics modules – this replaces prior use of nudging (to precipitation and GOES cloud top pressures)
4.  Data Format Changes
- The Land mask is being re-defined in the GRIB output such that LAND=0 over open-sea and sea-ice, and LAND=1 over land.  Previously
LAND=0 over open-sea, and LAND=1 over land *and* sea-ice.
- The sign of the sensible and latent heat fluxes are changing so that now these fluxes are defined as positive upwards, e.g. typical daytime fluxes are positive.  Previously
these fluxes were defined as negative upwards.

In addition to these system differences, product additions to existing grid files on the NCEP and NWS ftp servers will increase their size as follows:

1.  32 km North America (NCEP grid 221)
- The average size of these files will increase from ~89 MB to ~98 MB per file (time step).
- The following fields will be added:
- omega @ 10, 20, & 30 mb
- height, temperature, U & V winds, RH, and specific humidity @ 10, 20, & 30 mb
- derived radar reflectivity @ 1 km and composite
- cloud ceiling height
- instantaneous outgoing top of atmosphere longwave radiation
- dew point @ 2 m
- dominant precip type (will replace categorical precipitation types)
- lifted cloud level pressure
- total column supercooled liquid water and melting ice
- geometric vertical velocity (dz/dt) on all pressure levels (1000 - 5 mb)
- top and bottom of supercooled liquid water layer
- TKE on second lowest model level above surface
- This will affect data on the NCEP ftp server located at:
ftpprd.ncep.noaa.gov/pub/data/nccf/com/nam/prod/nam.{YYYYMMDD}/nam.t{CC}.awip32{FF}.tm00
where YYYYMMDD is the current date, CC is the model cycle time (00, 06, 12, or 18), and FF is the forecast hour (00-84).
2.  12 km Continental US (CONUS) surface data in GRIB1 format (NCEP grid 218)
- The average size of these files will increase from ~47 MB to ~48 MB per file (time step).
- The following fields will be added:
- derived radar reflectivity @ 1 km and composite
- cloud ceiling height
- dew point @ 2 m
- dominant precip type (will replace categorical precipitation types)
- total column supercooled liquid water and melting ice
- top and bottom of supercooled liquid water layer
- This will affect data on the NCEP ftp server located at:
ftpprd.ncep.noaa.gov/pub/data/nccf/com/nam/prod/nam.{YYYYMMDD}/nam.t{CC}.awip12{FF}.tm00
where YYYYMMDD is the current date, CC is the model cycle time (00, 06, 12, or 18), and FF is the forecast hour (00-84).

- This will affect data on the NWS ftp server located at:
tgftp.nws.noaa.gov/SL.us008001/ST.opnl/MT.nam_CY.{CC}/RD.{YYYYMMDD}/PT.grid_DF.gr1/fh.{FFFF}_tl.press_gr.awip12
where YYYYMMDD is the current date, CC is the model cycle time (00, 06, 12, or 18), and FFFF is the forecast hour (0000-0084).
3.  12 km CONUS 3-D data in GRIB2 format (NCEP grid 218)
- The average size of these files will increase from ~21 MB to ~29 MB per file (time step).
- The following fields will be added:
- dew point @ 2 m
- PBL height
- geometric vertical velocity (dz/dt) on all pressure levels (1000 - 5 mb)
- This will affect data on the NWS ftp server located at:
tgftp.nws.noaa.gov/SL.us008001/ST.opnt/MT.nam_CY.{CC}/RD.{YYYYMMDD}/PT.grid_DF.gr2/fh.{FFFF}_tl.press_gr.awp218
where YYYYMMDD is the current date, CC is the model cycle time (00, 06, 12, or 18), and FFFF is the forecast hour (0000-0084).
4.  12 km CONUS 3-D data in GRIB1 tiled format (54 subset tiles of NCEP grid 218)
- The average size of these files will increase from ~1.6 MB to ~1.8 MB per file (time step).
- The following fields will be added:
- dew point @ 2 m
- PBL height
- geometric vertical velocity (dz/dt) on all pressure levels (1000 - 5 mb)
- This will affect data on the NCEP ftp server located at:
ftpprd.ncep.noaa.gov/pub/data/nccf/com/nam/prod/nam.{YYYYMMDD}/tiles.t{CC}z/nam.t{CC}.awp218{FF}.{GG}
where YYYYMMDD is the current date, CC is the model cycle time (00, 06, 12, or 18), FF is the forecast hour (00-84), and GG is the grid number (01-54).
5.  45 km Alaska data (NCEP grid 216)
- The average size of these files will increase from ~9.8 MB to ~10.2 MB per file (time step).
- The following fields will be added:
- height, temperature, U & V winds, RH, and specific humidity @ 10, 20, & 30 mb
- PBL height
-This will affect data on the NWS ftp server located at:
tgftp.nws.noaa.gov/SL.us008001/ST.opnl/MT.nam_CY.{CC}/RD.{YYYYMMDD}/PT.grid_DF.gr1/fh.{FFFF}_tl.press_gr.awipak
where YYYYMMDD is the current date, CC is the model cycle time (00, 06, 12, or 18), and FFFF is the forecast hour (0000-0084).
6.  0.4 degree Hawaii data (NCEP grid 243)
- The average size of these files will increase from ~9.8 MB to ~10.3 MB per file (time step).
- The following fields will be added:
- height, temperature, U & V winds, RH, and specific humidity @ 10, 20, & 30 mb
- This will affect data on the NCEP ftp server located at:
ftpprd.ncep.noaa.gov/pub/data/nccf/com/nam/prod/nam.{YYYYMMDD}/nam.t{CC}.awiphi{FF}.tm00
where YYYYMMDD is the current date, CC is the model cycle time (00, 06, 12, or 18), and FF is the forecast hour (00-84).
7.  NAM native grid - surface fields (egrdsf files)
- The average size of these files will increase from ~86 MB to ~96 MB per file (time step).
- The following fields will be added:
- instantaneous outgoing top of atmosphere longwave radiation
- dew point @ 2 m
- evaporation @ surface
- potential evaporation @ surface
- land surface precipitation accumulation
- Latitude & Longitude
- This will affect data on the NCEP ftp server located at:
ftpprd.ncep.noaa.gov/pub/data/nccf/com/nam/prod/nam.{YYYYMMDD}/nam.t{CC}.egrdsf{FF}.tm00
where YYYYMMDD is the current date, CC is the model cycle time (00, 06, 12, or 18), and FF is the forecast hour (00-84).

- This will affect data on the NWS ftp server located at:
tgftp.nws.noaa.gov/SL.us008001/ST.opnl/MT.nam_CY.{CC}/RD.{YYYYMMDD}/PT.grid_DF.gr1/fh.{FFFF}_tl.press_gr.egrdsf
where YYYYMMDD is the current date, CC is the model cycle time (00, 06, 12, or 18), and FFFF is the forecast hour (0000-0084).
8.  NAM native grid - 3-D fields (egrd3d files)
- The average size of these files will increase from ~250 MB to ~530 MB per file (time step).
- There will be numerous additions to these files to support all of the new fields list in the above files.
- This will affect data on the NCEP ftp server located at:
ftpprd.ncep.noaa.gov/pub/data/nccf/com/nam/prod/nam.{YYYYMMDD}/nam.t{CC}.egrd3d{FF}.tm00.gz
where YYYYMMDD is the current date, CC is the model cycle time (00, 06, 12, or 18), and FF is the forecast hour (00 & 06).

NCEP Central Operations is currently running the WRF/NMM in its parallel operations.  Output from these runs will be made available on the NCEP ftp server beginning the week of March 20, 2006.  These parallel data will remain on this server until the WRF/NMM is implemented on June 13, 2006.  This will allow users the opportunity to become familiar with the WRF/NMM system.  The location of these parallel data on the NCEP ftp server will be at:

ftpprd.ncep.noaa.gov/pub/data/nccf/com/nam/para

Please direct any questions regarding this change to:

NCEP.List.PMB-PCSP@noaa.gov

Sincerely,

NCEP Central Operations