# URMA ceiling clearing boundary

Independent ecCodes reads of ceiling and total cloud cover at July 27, 2020 11:00 and 12:00 UTC confirm a change in the checked source pair. Among cells with cloud cover below 50%, 1,208,171 of 2,280,125 ceiling cells (52.987%) are at 16,000 m at 11:00 UTC, compared with all 2,084,989 cells at 12:00 UTC. This does not map every earlier or later hour, and makes no corresponding claim about visibility.

The joint [NOAA RTMA/URMA v2.8 science brief](https://www.emc.ncep.noaa.gov/users/impldocs/rtma_urma_v2.8_science_brief.pdf), page 14, describes assigning the maximum ceiling when cloud cover is below 50%. The observed source boundary and any release notice date are separate evidence; exact historical deployment provenance is not established here.

[Source offsets, message hashes and counts](ceiling-clearing-evidence.json). Source files: [11:00 UTC](https://noaa-urma-pds.s3.amazonaws.com/urma2p5.20200727/urma2p5.t11z.2dvaranl_ndfd.grb2_wexp), [12:00 UTC](https://noaa-urma-pds.s3.amazonaws.com/urma2p5.20200727/urma2p5.t12z.2dvaranl_ndfd.grb2_wexp).