Slitherine

It should be useful to change the climate during scenarios to simulate weather conditions better. This can be particular useful if scenarios progress several days per turn while heavy rain or thaw turns ground to mud.

+1
This could add some nice uncertainties, especially to the east front with (a bit random) starts of mud-snow-turns.
Or sandstorm in NA, or heavy rain squalls in naval scenarios where carriers could hide or......

If a dev with coding skill is still looking for an awesome idea for posterity...
Even the old Panzer Corps from 2011 could do that (although with a terrible random generator).