NOUS41 KWBC 071140 AAD
Implementation Notice 11-16, Amended
Implementation Date Delayed: Changes to
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
Details on the various changes are provided below, along with a notice about possible changes to product generation time.
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
All model changes will also be applied to the Downscaled GFS by NAM Extension (DGEX) forecast system.
a) Initial first guess
at T-12hr will reflect relocation of
Changes to the Gridscale Statistical Interpolation (GSI) analysis:
a) New faster version
of the GSI code with new observation error
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
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
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
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,
- 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
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
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
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:
NCEP/Mesoscale Modeling Branch
Camp Springs, Maryland
301-763-8000 X 7221
NCEP/Mesoscale Modeling Branch
Camp Springs, Maryland
301-763-8000 X 7227
For questions regarding the dataflow aspects of these datasets, please contact:
NCEP/NCO Dataflow Team
Camp Springs, Maryland 20746
301-763-8000 X 7198
NWS National Technical Implementation Notices are online at: