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065
NOUS41 KWBC 251942
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
John.Derber@xxxxxxxx
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@xxxxxxxx
NWS National Technical Implementation Notices are online at:
http://www.weather.gov/os/notif.htm
$$
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