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Using NJ to read GRIB-2 NCEP datasets

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  • Subject: Using NJ to read GRIB-2 NCEP datasets
  • Date: Thu, 21 Aug 2014 22:55:17 +0000
John,

A Panoply user reported an issue with viewing NOAA NCEP forecast data that is 
saved in GRIB-2 format. Since Panoply uses NJ to actually decode the datasets, 
and as I haven’t been able figure out the problem looking at the NJ source 
code, I’m passing this along to you.

The datasets are located at
ftp://ftp.ncep.noaa.gov/pub/data/nccf/com/gfs/prod/gfs.2014082112/

Specifically, we are looking at the files at approximately the middle of that 
directory that have names like gfs.t12z.pgrbfNNN.grib2

The problem is that the information reported by NJ about the time interval for 
the quantities in these files apepars to be wrong. For example, the 
gfs.t12z.pgrbf384.grib2 dataset has 384-hour forecast information, which the 
wgrib2 or grib2scan command-line tools report. However, NJ is returning the 
quantities as 144-hour average.

There are time interval errors occuring with other datasets, e.g., the 24-hour 
forecast quantities in gfs.t12z.pgrbf24.grib2 are instead reported as 6-hour 
average.

rbs



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Robert B. Schmunk
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NASA Goddard Institute for Space Studies
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