Slitherine

And I'm not talking about the 1 meter of snow covering my garden.

I wish we were able to trigger a climate change in a scenario as these changes, especially on the east front, were very important.
Clear to mud, mud to winter and back.

I don't mind the game doing a reload between turns to update terrain and terrain effects.

My vote for this!
A general sight-range reduction like half/min-1 during snow-, rainfall, and sandstorms (hello Africa!) is highly welcomed too!
I doubt there is such a huge loading/RAM required to switch textures and colors compared to loading 3d-models in this game. Switching camos of units doesn't require a reload either.

And air activities should be prohibited/restricted in snow and maybe rain.
Maybe the regular airfields could be all-weather and the airstrips only working in cllear weather.

I remember how aggravating it was in Perfect General I think it was where you get all your units ready to pounce on a town with various enemy around then all of a sudden you can't move that extra hex and your planes are grounded or you can get the job done in 2 more turns but nope not now the weather changed not its impossible problem is I often turned the weather off to much headache after being at work all day then having to fight the weather inside my own house but its a great option to have.