Background information about the characteristics of this data may be
found in An Introduction to Atmospheric and Oceanographic Datasets.
There is general basic information in its Introduction .
More specific information may be found in these chapter(s) or section(s):
Analyzed and Model Data .
You may wish to refer to Other Sources of Data .
Note that NCEP also made the Aviation (AVN) Analyses using the same model, but DSS
did not not collect them.
INFORMATION ABOUT THE NCEP GDAS FNL 1.0 DEGREE 6-HOURLY ANALYSIS UPDATES
In our monthly data directories, filenames have the form fnl_yymmdd_hh_00 ,
the yymmdd_hh is in Coordinated Universal Time (UTC, UT, GMT or Z). The
_00 in this form indicates that the file is an analysis, not a forecast.
The "NCEP POSTED" column is the C.U.T. time when NCEP posted the file on
their server. (When I populated the July 2002 - early September 2003
directories, this time is just the time I uploaded the files from the
NCAR MSS). The "BYTES" column shows the file size, which varies from
about 22MB to 24MB, due to the dynamic nature of the GRIB data format,
and changes in the number and kinds of fields available. If you find
fields in recent files which are not available in the older files, be
advised that NCEP will not be recreating them. NCEP prepares these on
an operational basis.
I download the FNL analysis files from the NCEP file server, from the
/pub/data/nccf/com/fnl/prod/fnl.[date] directory, where date has the form
yyyymmdd , and the files are named gdas1.thhz.pgrbf00 where hh is the analysis
time and f00 indicates an analysis. pgrb files with other fnn values are
forecasts nn hours into the future. You will find numerous other files in
this directory
I do not get the GFS (formerly AVN) files, which are prepared with a smaller
observational data base. I.e., the FNLs are prepared later, after NCEP collects
more of the observations. NCEP makes the GFS (AVN) about 2:45 after the
synoptic time, and the FNLs about 5:00 after synoptic time, posting the FNLs
on their server about 6:00 after the synoptic time, and then I get it within
1:00 of that. These times can vary by a few hours. NCEP's operational
responsibilities to U.S. aviation and others get priority, and the FNLs get
less priority, although I believe they are used to initial subsequent forecasts.
Acquiring the FNLs, not the AVNs, is our objective... Please see the NCEP
document About the Global Parallel System .
and the EMC Model Documentation .
I do not collect the forecasts for two reasons. Our space limitations and
our primary mission to support long period research, rather than real time
interests. It is the UCAR UNIDATA mission
to support near real time data needs.
My script searches for the latest files every 20 minutes. The script is
started every 3 hours, and runs for 2 hours. Traffic on this server can be
very heavy, so to be courteous to other users, I do not try any more often
than that. Compare our file download times to NCEP's file posting times
(Eastern time zone), and if you need and believe that you could do better, I
have above provided all the information to do it yourself. For additional
information about the NCEP server, contact the NCEP Helpdesk.
When NCEP does not post the data, or my scripts fail, I must contact NCEP
staff to recover the data. This can take a week or two. This has enabled
us to maintain a near perfect period of record since January 2000. However,
I can not guarantee to users that we can support timely postings on our
FTP site.
TYPES:
Operational
Gridded analyses
Synoptic
Surface analyses
Upper air analyses
Sea analyses
Oceanographic
COVERAGE:
Global coverage
Latitude / longitude grid
PERIODS:
Complete except for dropouts in 1999
TIMES:
daily 12-hourly 6-hourly
at 00Z, 06Z, 12Z and 18Z
VARIABLES:
Land skin temperature and sea surface temperature are in one field.
A level/variable table of a recent data file is
here.
LEVELS:
1000mb 975mb 925mb 900mb 850mb 800mb 700mb 650mb 600mb 550mb 500mb 450mb 400mb
350mb 300mb 250mb 200mb 150mb 100mb 70mb 50mb 30mb 20mb 10mb
surface upper-air troposphere mandatory tropopause stratosphere
FORMAT:
Be aware of these processing issues.
MM5, WRF and RAMS users click here.
A little advice is available for: GRIB and GrADs (display) software
VOLUME:
Blocks are variable in size, due to the dynamic packing of GRIB.
90MB/day 2.7GB/month 33GB/year
COST:
You will find the latest available year's data, free, by clicking the 
tab in the navigation bar. All the data are available on the NCAR MSS.
Users with NCAR computing accounts have free access from the NCAR MSS through clicking the tab in the navigation bar.
For all others, costs depend on the amount requested, and the DSS standard charging rate applies unless their order qualifies for our lowest reduced charging rate, aka "half direct copy rate" as shown on the service charges page.
To send a data request to a staff member, please use this form.
