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GLOBAL FORECAST SYSTEM
Upcoming Implementations:
2013
Semi-Lagrangian with resolution increase to T1148L64
Also view the Research and Development page to see what we're working on.
Latest Implementation:
Correction to Land Surface Model in Global Forecast System and associated cool and moist bias in near surface temperature and moisture fields
Beginning with the 1200 Coordinated Universal Time (UTC) model run on Wednesday, September 5, 2012, the National Centers for Environmental Prediction (NCEP) Central Operations will implement a correction to the Land Surface Model used to drive the Global Forecast System (GFS). This correction is expected to improve the cool and moist bias in the near surface air temperature and moisture fields during the warm season.
Starting in mid-June 2012 NCEP was informed about a problem with the GFS near surface temperature and moisture simulations verifying in the late afternoon over the central US where drought conditions existed. Specifically, customers noted that a significant 2m cold and wet bias existed in both the MOS and GFS gridded products. Modelers at the NCEP Environmental Modeling Center (EMC) responsible for development of the GFS and scientists at the Meteorological Development Laboratory (MDL) identified the cause in late June. The problem was traced to a look-up table used in the land surface scheme that modulates evapotranspiration based on vegetation type and root zone depth. Current settings allowed for excessive transpiration and plant-extraction of soil moisture from deeper soil layers causing the lower atmospheric boundary layer to become too moist and cool.
EMC conducted a parallel test of the GFS with corrected land surface parameters starting in early June and running through late August, to determine if appropriate modifications to the LSM look-up table would provide a correction to the cold/wet bias without having an unexpected negative impact on other meteorological fields over the US and the globe. EMC conducted an assessment of the GFS parallel and found the change to the land surface model significantly reduced the cold/wet bias over the US and improved the 0-3 day precipitation forecasts. In addition, MDL conducted an objective evaluation of the GFS MOS guidance generated from the GFS parallel output. MDL concluded that the corrections in the GFS parallel output had the desired effect of reducing the cold/wet bias resulting in improved bias and error scores in the GFS MOS temperature and dewpoint guidance. Slight improvement was also noted in the GFS MOS probability of precipitation guidance generated from the GFS parallel output. A summary of MDL's evaluation and comparisons of GFS MOS text bulletins generated from the GFS parallel output can be viewed at
http://www.mdl.nws.noaa.gov/~mos/mos/gfs_coolfix/comp_mavmex.php
NCEP (and MDL) also conducted a 1.5 month GFS parallel evaluation for the period Jan-Feb 2012 to test the land surface model correction during the US cold season. As expected, analysis of results indicate that the change in the land surface model had little impact on the simulated 2m temperature and dewpoint given the low solar forcing during the winter months. MDL's analysis of the MOS guidance from the GFS parallel during the cool season sample also indicated minimal impact on the 2m temperature and dewpoint.
Based on the positive results of the GFS parallel tests and the severity of the cold and wet bias in the near surface air temperature, the NCEP Director has approved implementation of the correction to the land surface model. NCEP Central Operations plans to implement the change beginning with the 1200 UTC cycle on 5 September 2012.
We want to express or thanks to those customers who brought this problem to our attention in June. NCEP also appreciates your patience as we needed time to adequately test the GFS to ensure that correcting the land surface model did not have adverse and unexpected negative impacts on other forecast guidance (i.e., precipitation, hurricane track, hemispheric wave patterns, etc.).
Click to view analysis of parallel test results
For questions regarding the correction to the GFS Land Surface Model and resulting improvement to the near surface cold and moist bias please contact:
Bill Lapenta
NCEP EMC/College Park, Maryland
301-683-3700
Bill.Lapenta@noaa.gov
For questions regarding the impacts on the GFS MOS text and gridded products please contact:
Kathryn Gilbert
MDL/Silver Spring, Maryland
301-713-0023, Ext. 130
Kathryn.Gilbert@noaa.gov
For questions regarding the impacts to the GFS LAMP text and gridded products please contact:
Judy Ghirardelli
MDL/Silver Spring, Maryland
301-713-0056, Ext. 194
Judy.Ghirardelli@noaa.gov
Links to the MOS products and descriptions are online at:
http://www.nws.noaa.gov/mdl/synop
NWS national TINs are online at:
http://www.weather.gov/os/notif.htm
_________________________________________________________________________________________________________________
Previous Implementations:
Hybrid EnKF - 3DVar GSI data assimilation
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
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 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@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
GFS 9.0.1
Now effective May 9, 2011, at 1400 UTC. Read upgraded TIN
Effective May 9, 2011, beginning with the 1200 Coordinated Universal Time (UTC) run, the National Centers for Environmental Prediction (NCEP) will upgrade the GFS. Read full TIN
- Analysis Changes:
- Improve Ozone Monitoring Instrument (OMI) quality control
- Remove redundant SBUV/2 total ozone
- Retune SBUV/2 ozone observation errors
- Relax AMSU-A Channel 5 quality control
- Update Community Radiative Transfer Model(CRTM) to version 2.0.2
- Include field of view size/shape/power for radiative transfer
- Remove down weighting of collocated radiances
- Limit moisture >= 1.e-10 in each outer iteration and at end of analysis
- Include uniform (higher resolution) thinning for satellite radiances
- Improve location of buoys in vertical (move from 20m to 10m)
- Improve Gridpoint Statistical Interpolation (GSI) code with optimization and additional options
- Recompute background errors
- Include SBUV from NOAA-19
- Ambiguous vector quality control for ASCAT (type 290) data
- Model Changes:
- Set new thermal roughness length
- Set minimum moisture value in Stratosphere to 1.0x10-7
- Reduce background diffusion in the Stratosphere
- Product Changes:
- Correct error in the 192 hr, 12-hr precipitation bucket
- Addition of a new membrane sea level pressure (SLP) field to the 0.5, 1.0 and 2.5 degree pressure grib (pgrb) files only. This pressure is generated by first relaxing the underground virtual temperature and then integrating the hydrostatic equation downward. The field will be subject to Spectral Gibsing near the coast, but this will be addressed in a future implementation.
- increased low level warm bias over land
- negative temperature bias in the stratosphere
- negative wind speed bias in the stratosphere
- error in the calculation of the 12 hr accumulated precipitation at 192 hrs only.
- The format and content of all GFS data sets will remain unchanged, with the exception of the addition of the new SLP field. GFS data is currently available on NOAAPORT, the NWS FTP server, the NCEP server and in NOMADS. The location of the data will remain unchanged.
- Product delivery timing of the GFS products is not expected to change as a result of this implementation. 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 mid-March. The parallel data will be 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
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 |
John H. Ward NCEP/EMC, Global Climate and Weather Modeling Branch Camp Springs , Maryland 301-763-8000 x 7185 John.Ward@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
T574 W/ NEW PHYSICS - July 27th 2010
Effective July 27th 2010 12 UTC cycle the National Centers for Environmental Prediction (NCEP) upgraded the Global Forecast System (GFS).
Read the complete TIN
Model changes:
- Resolution increase: T382 (35 km) -> T574 (27 km)
- High resolution portion of forecast will be extended from 180 hrs -> 192 hrs
- Significant changes in the definition of parameters in the 192 hr pressure grib (pgrb) and flux files
- Also a significant change in model physics associated with this change
- Additional modifications will be made to the contents of the Global Data Assimilation System (GDAS) and GFS pgrb files
- Changes in model physics include:
- Radiation and cloud overlap
- Gravity wave grad
- Hurricane relocation
- New planetary boundary layer scheme
- New mass flux shallow convection
- Updated deep convection scheme
- Positive definite tracer transport scheme
- New parameter for the GFS forecast pressure grib file:
- Max wind gust
- Several parameters are being deleted from the GDAS analysis pressure grib files because they are not valid for the analysis dataset and have never provided pertinent information:
- 4 precipitation types
- Convective precipitation rate
- Land sea mask
- Latent heat flux
- Sensible heat flux
- Precipitation rate
- 2 m RH
- 2 m specific humidity
- 2 m temperature
- Boundary layer cloud cover
- Low cloud cover
- Convective cloud cover
- Skin temperature
- Surface upward long wave flux
- Surface upward short wave flux helicity
- These parameters are being deleted from the Global Forecast Model simulated GOES grib file because they were included in error:
- Mean sea level pressure
- WAVE-5 geopotential height
- All accumulated or averaged values in the 192 hr pgrb and flux files will now be over a 6 hour period instead of 12 hours
- The format and content of the 3 hourly files from 180 to 192 hours will be the same as the files from 0 to 180
- For the flux file this includes the majority of the parameters in the files
- Parameters changing in the pgrb file:
- 2 m above ground max. temperature
- 2 m above ground min. temperature
- Surface albedo
- Surface clear air UV-B downward solar flux
- Surface categorical freezing rain
- Surface categorical ice pellets
- Surface convective precipitation rate
- Surface categorical rain
- Surface categorical snow
- Atmospheric column cloud work function
- Surface downward long wave flux
- Surface downward short wave flux
- Surface UV-B downward solar flux
- Surface ground heat flux
- Surface latent heat flux
- Surface precipitation rate
- Low cloud base pressure
- Low cloud top pressure
- Mid-cloud base pressure
- Mid-cloud top pressure
- High cloud base pressure
- High cloud top pressure
- Surface sensible heat flux
- Atmospheric columb total cloud cover
- Boundary cloud layer total cloud cover
- Low cloud cover
- Mid-cloud cover
- High cloud cover
- Low cloud top temperature
- Mid-cloud top temperature
- High cloud top temperature
- Surface zonal gravity wave stress
- Surface zonal momentum flux
- Surface upward long wave flux
- Top of atmosphere upward long wave flux
- Surface upward short wave flux
- Top of atmosphere upward short wave flux
- Surface meridional gravity wave flux
- Surface meridional momentum flux
- Surface convective precipitation
- Surface total precipitation
- Surface large scale precipitation
Note: For the 192 hr pgrb products available on NOAAPORT and in AWIPS the accumulations and averages will remain over the previous 12 hour period until AWIPS is modified to accommodate this change.
One additional change to note: The file pgrbf192.grib2 on the NCEP FTP server will change from containing model output on a 2.5 degree grid to containing model output on a 1 degree grid. The 2.5 degree output will be provided in a new file with the name pgrbf192.2p5deg.grib2.
The format of the 1/2 and 1 degree pressure grib files will remain the same except for the changes in variables listed above. The size of these files will nto change significantly. With the increase in model resolution...the size of the sigma coefficient files and the surface flux files will increase significantly.
If you have any questions concerning these changes, please contact:
| John H. Ward NCEP...Global Modeling Branch Camp Springs, Maryland Phone: 301-763-8000 X7185 Email: John.Ward@noaa.gov |
Shrinivas Moorthi NCEP...Global Modeling Branch Camp Springs, Maryland Phone: 301-763-8000 X7233 Email: Shrinivas.Moorthi@noaa.gov |
Read the complete TIN