The IEM produces composites of N0Q (8 bit Base Reflectivity) NEXRAD data every five minutes for a domain that covers the CONUS. The original intent of the N0Q composites was to provide imagery at a data resolution of 0.5 dBZ. After some investigation, it was discovered that the N0Q composites only contained data at values of whole integer values of dBZ. After some debugging of GEMPAK, the issue was hopefully fixed within GEMPAK. The good news is that this bug did not impact any end-user processing of the file. The conversion of color index and RGB colors to dBZ was OK. There just was not any data at those 0.5 dBZ, non-int values.

Restating and for example, you would find reflectivity values at 40 dBZ and 41 dBZ, but not 40.5 dBZ. This change did inflate the file size by 40%, with all the extra colors now included.

Also to note, eventually the NWS is going to stop disseminating the lower resolution N0R dataset (maybe Dec 2016?). At that point, the IEM will stop creating composites of N0R. In general, migrating your web mapping app that uses IEM services should be as easy has changing 'n0r' to 'n0q' in the various URIs. There will be more news items posted here when that date becomes more firm.