NOUS41 KWBC 251842 AAB
PNSWSH
Technical Implementation Notice 12-22,
Amended
National Weather Service Headquarters
Washington DC
342 PM EDT Wed Apr 25
2012
To:
Subscribers:
-Family of Services
-NOAA
Weather Wire Service
-Emergency Managers Weather Information Network
-NOAAPORT
Other
NWS Partners, Users and Employees
From:
Timothy McClung
Science Plans Branch Chief
Office of Science and Technology
Subject: Amended: Global
Forecast System (GFS) Upgrade:
Effective May 22, 2012
Amended to correct information about
availability of new pressure and specific humidity fields, specify the labeling
of the layer CAPE and CIN, and include a note about the Haines index
field. All of these changes are included
in the "GFS Output Product Changes" section of this TIN.
Effective on or about Tuesday, May 22,
2012, beginning with the 1200 Coordinated Universal Time (UTC) run, the National Centers for Environmental Prediction
(NCEP) will upgrade the GFS model and its associated data assimilation system
(GDAS). The primary changes will be to
the analysis system. There will be no major changes to the GFS model itself,
but there will be a few modifications to the output products available from the
GFS.
The primary change to the operational GFS
and GDAS will be in the analysis system. The major component of the
analysis change will be the incorporation of a hybrid variational/ensemble
assimilation system. In this system, the background error used to project
the information in the observations into the analysis is created by a
combination of a static background error (as in the prior system) and a new
background error produced from a lower resolution (T254) Ensemble Kalman Filter. The development of this system was done in collaboration with PSD at ESRL. The
inclusion of this change and the other smaller changes listed below produce
significant positive impact on forecasts in both the northern and southern
hemispheres and in the tropics. In almost all measures, a positive impact
is noted; however, during the summer (convective precipitation) season, a
small consistent degradation of the rain/no rain line and an increase in the
bias was noted. This problem will be addressed through modifications to
the convective parameterization in the next global implementation.
Additional changes in this upgrade include:
Analysis Changes:
-- Use GPS RO bending angle rather than refractivity
-- Include compressibility factors for atmosphere
-- Retune SBUV ob errors, fix bug at top
-- Update radiance usage flags
-- Prepare for monitoring NPP and Metop-B
satellite data
-- Add NPP ATMS satellite data
-- Add GOES-13/15 radiance data
-- Add SEVERI CSBT radiance product
-- Include satellite monitoring statistics code in operations
-- Add new satellite wind data and quality control
-- Update to current version of analysis trunk for optimization and
preparation for future updates
GFS Model
Changes:
The global spectral model is restructured,
but there are no major physics or dynamics changes except for some bug fixes.
The impact of these changes on the forecast is at the machine round off level.
GFS Output Product Changes:
- CAPE,
CIN, and Lifted Index fields will now be calculated from virtual temperature.
- Users will see
minor changes in simulated GOES products due to the use of the newer CRTM 2.0.2
library and coefficient files.
- The following
fields will be added to the 0.5, 1 and 2.5 degree pressure GRIB files
Haines
index
Transport
U and V
Ventilation
Rate
Best
300mb Cape and CIN and their source levels
Temperature, U and V winds at 80 and 100m
Specific humidity and pressure at 80m
The Haines index will be labeled with a
GRIB parameter number of 3 at this time, but with an upcoming change the GRIB
parameter number will change to 2. A TIN
will be issued announcing this change.
The Best 300mb CAPE and CIN are encoded in
GRIB as level 255 due to a limitation in GRIB encoding.
1km helicity will
be removed from the 0.5, 1 and 2.5 degree pressure GRIB files. This field was added to these files by
mistake during a previous implementation.
Data Availability:
The format and content of all current GFS
data sets will remain unchanged, with the exception of the
addition of the new fields. GFS data are currently available on
NOAAPORT, the NWS FTP server, the NCEP server and in NOMADS. The location of these data will remain unchanged. The
additional new fields will be available only on the NWS and NCEP FTP servers.
Product delivery timing of the majority of GFS
products is not expected to change as a result of
this implementation. The GFS Downscaled Guidance (DNG) for Guam will be delayed
for all forecast hours from hour 2 to 192. The delay will accumulate through
the forecast hours and may be as much as 20 minutes by forecast hour 192.
More information regarding the GFS and associated products can be found at:
http://www.emc.ncep.noaa.gov/GFS/doc.php
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-April.
The parallel data are available via the following URLs:
http://www.ftp.ncep.noaa.gov/data/nccf/com/gfs/para
ftp://ftp.ncep.noaa.gov/pub/data/nccf/com/gfs/para
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:
John Derber
NCEP/EMC, Global Climate and Weather
Modeling Branch
Camp Springs , Maryland
301-763-8000 x 7740
For questions regarding the dataflow
aspects of these data
sets,
please contact:
Rebecca Cosgrove
NCEP/NCO Dataflow Team
Camp Springs , Maryland 20746
301-763-8000 x 7198
ncep.list.pmb-dataflow@noaa.gov
NWS National Technical Implementation
Notices are online at:
http://www.weather.gov/os/notif.htm
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