WRF Feature, Capabilities, Infrastructure Testing For the release, a number of existing capability options in the WRF code need to be explicitly tested to insure the continued correct working of the model for users. Among these tested options are: adaptive time step analysis nudging observational nudging digital filtering initialization diffusion options program NDOWN program OBSGRID sst update global domain vortex following (moving nest) While the testing of some of the new physics options is done for 28 48-h time periods, all of the new physics options are run through a couple of canned cases, and verified with subjective analysis. The level of success is easier to achieve, generally producing a complete forecast that gives reasonable results. The specific new additions to the model are scrutinized much more closely. An important consideration for this level of testing is the interworking of schemes, from source-code incompatibility to the consequences of unphysical results. Testing for these new features includes: aerosols (Goddard, Thompson, RRTMG) CLM Grell Freitas cumulus Grenier Bretherton PBL GRIMS shallow cumulus scheme KF-cup cumulus scheme lightning options 1, 2, 11 Morrison Gettleman microphysics New Tiedke cumulus scheme NoahMP land surface Noah subgrid tiling NSSL microphysics options 17, 19, 21 NWP diagnostics ozone options 0, 2 sea ice scale aware cumulus scheme SKEBS (backscatter scheme) TEMF PBL Scheme topo_wind option 2 trajectories urban physics 1, 2, 3 For each of the above tests (types of land data, various physics options, feature upgrades, previous capability re-assurances), a fixed set of permutations were conducted: single domain case, concurrent nesting, restart, nested restart The restart runs compared output from an original end-to-end run to the restarted simulation to ensure the two data sets were bit-wise identical. Additionally, several of the above combinations of namelist settings were tested as follows: ndown, one-way-nest, nest-starts-later As part of the assurance that the WRF code is not suffering from accidental side-effects, all of the idealized cases have been run, comparing the previous release and the current WRF 3.8 release. The cases all build, run, and produce similar results. As some of the cases use physics schemes that have been upgraded, it is not really possible to get identical results in most of these tests. This portion of the testing handles all of the lateral boundary condition options in WRF, and exercises many of the dynamics switches. The feature testing was conducted on a Linux platform. All tests were run with MPI (with the exception of the idealized cases, which were run serially) for both Intel V12.1.5 and GNU V4.8.2. The following are known to NOT give bit for bit identical answers with a restart: Global Run ncd_nofill = .true. lightning options 1, 2, 11 NSSL option 17 needs a small time-step (4xDX).