Problem: In this release, the restart capability is broken, unless one restarts from a boundary condition time. This means if one has 6 hourly lateral boundary conditions, and if one restarts at 6 hourly interval, restart works fine. Restarting from at times between the boundary times may fail.
Solution: We are looking for a fix to the problem.
diff_opt = 2 Problem with V3.9.1 Release
Problem: In the file dyn_em/module_diffusion_em.F, some undefined k indices were used outside k loops instead of kts. This happened in one line of the recently changed (since V3.9.1) code to fix the slope terms in diff_opt=2. This affects the v-wind component computation in the y direction at the surface over sloped terrain. This problem only occurs when using the diff_opt = 2 option, along with the use of terrain data, in the y direction (e.g., this would apply to all real data cases over land. This would not apply to any of the idealized cases, unless terrain was added. This does not apply to the hill_2d_x case, as it is x-direction specific).
Solution: Replace your dyn_em/module_diffusion_em.F file with this file. Go back to WRFV3/ and recompile. It is not necessary to issue a 'clean -a' or to reconfigure. Simply recompile, and the compilation should be fairly quick.