# Archive and mirror chronology

Iowa State's archive has separate CONUS RTMA files at 108 of these timestamps; decoded examples use a different 2145×1377 grid and are not equivalent replacements.

The NODD boundary precedes the nominal v2.7 cycle by 18 hours. Separate Iowa CONUS visibility files on a different grid change between December 4 11Z and 12Z, matching NOAA's notice. NODD's files were uploaded in August 2023; the reason for the product/archive discrepancy is unconfirmed.

These observations do not establish an irreversible archive-wide transition or which historical executable generated every hour. The cause of the NODD archive gaps remains unconfirmed.

Evidence: [Iowa file-presence checks](iowa-presence.json), [decoded mirror examples](mirror-checks.json), [Iowa boundary checks](iowa-boundary.json), [source/store boundary](boundary-verification.json), and the [NOAA v2.7 notice](https://www.weather.gov/media/notification/pdfs/scn18-96rtma_urma_2.7_aab.pdf).