NOTE: The nws-changes mailing list is no longer active. The list archives are made available for historical reasons.
-------- Original Message --------
536
NOUS41 KWBC 071140
PNSWSH
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
-NOAAPORT
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 NCEPs major modeling will be
performed within NEMS. This NAM upgrade represents the first
implementation of NEMS and a major step in the evolution of
NCEPs 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:
www.emc.ncep.noaa.gov/mmb/mmbpll/misc/nmmb_domains.png
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:
www.emc.ncep.noaa.gov/mmb/mmbpll/misc/sampleinv_namnests.html
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:
www.emc.ncep.noaa.gov/mmb/mmbpll/misc/NAM_Q32011_Upgrade.pdf
For more general information about the NAM and NDAS, please see:
http://www.emc.ncep.noaa.gov/NAM/
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:
http://www.ftp.ncep.noaa.gov/data/nccf/com/nam/para
ftp://ftp.ncep.noaa.gov/pub/data/nccf/com/nam/para
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
Geoff.DiMego@xxxxxxxx
or
Eric Rogers
NCEP/Mesoscale Modeling Branch
Camp Springs, Maryland
301-763-8000 X 7227
Eric.Rogers@xxxxxxxx
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
ncep.pmb.dataflow@xxxxxxxx
NWS National Technical Implementation Notices are online at:
http://www.nws.noaa.gov/os/notif.htm
$$
nws-changes archives: