The GSI cloud analysis for RTMA includes analyses of cloud hydrometeor (water and ice) mixing ratios, but not cloud fraction. Therefore, the cloud-cover (%) diagnostic algorithms in UPP must be modified to use these analyzed fields.

The proposed approach is to create a "synthetic" cloud-cover field using a fraction of exceedance within a 16.1 km (10 mile) radius. Namely, for every grid volume, a 16.1-km horizontal radius will be searched for neighboring volumes containing (Qc + Qi) > 10^–7 g/g. The fraction of exceedance found in this search will be assigned locally as the cloud cover.

A similar fraction-of-exceedance approach was used in earlier RAP/HRRR versions. The threshold mixing ratio in these versions was also 10^–7 g/g, but the search radius was larger (30 km).

This issue can be assigned to @jaymes-kenyon.

Copying several RTMA developers: @GangZhao-NOAA @guoqing-noaa @ManuelPondeca-NOAA @AnnetteGibbs-NOAA @MatthewMorris-NOAA @hu5970