[gradsusr] 13-km RUC fields file naming convention

[June Yeung]

Hi everyone,
I am trying to download 13-km resolution Rapid Update Cycle (RUC) 
analysis fields from the NOMADS site, but I am a little confused about 
the file naming convention.  For every hour, it seems that there are 
10-12 files (e.g., ruc2_130_20090808_0000_0##.grb2 where ## ranges from 
00 to 12).  See this catalog, for instance: 
http://nomads.ncdc.noaa.gov/thredds/catalog/ruc13/200908/20090808/catalog.html  
I thought 13-km resolution RUC fields are available on an hourly scale?  
Is anyone experienced with these data sets, by chance, and can help me 
to interpret what the last 3 digits represent?   Sorry if this is 
obvious.  I tried to look up the documentation but couldn't find what I 
need.
Thank you very much,
June

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June Yeung
Graduate Student
Department of Civil & Environmental Engineering
Princeton University