NOUS41 KWBC 131829

PNSWSH

 

Technical Implementation Notice 12-22

National Weather Service Headquarters Washington DC

230 PM EDT Fri Apr 13 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:    Global Forecast System (GFS) Upgrade:

            Effective May 22, 2012

 

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 major component of the analysis change will be the incorporating 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.  Including 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 has been 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, specific humidity, U and V winds at 80 and 100m

 

- 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 on the GFS and associated products is online 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@noaa.gov

 

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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