Hi, I'm trying to determine if this is grid resolved convection, or grid scale noise. This is a plot of max vertical velocity. Colors are +/- 50fpm. The peak to peak distance is approximately 2*dx, which makes me suspect noise. dx is 4km.
Definitely a noise. a) You should reduce time step or use adaptive time step, b) use the diff_6th_opt option. The latter one is a cosmetic solution as it smooths out the disturbances. But the first should resolve some of this issue.