Due to the scope of SR2020 we won't be including weather.
Thought I'd expand on this a little... While modeling weather is a long term goal of ours to include in the Supreme Ruler franchise, SR2020 won't have it. The development time is just not there this time around and we want to make sure we do it right! (my vision is having an option for a weather overlay that shows current type satellite weather maps to give you an idea of what's coming as well as what's already over the battlefield). Not only should weather affect combat, it should also affect energy consumption for heating and cooling as well as a host of other factors. As well, we would need to include seasonal satellite imagery --- a different high resolution satellite picture of the world for every month of the year, reflecting seasonal flood plains, snow covered terrain etc.. Which actually brings in an additional development challenge - how do you change the underlying Terrain Type of the map almost in mid game?
My guess is that we would need four to eight months dedicated to the weather model - mapping weather patterns, allowing for some random extra harsh weather (you know... like the Germans once ran into...), and addressing the other issues I mentioned.
Like Covert Ops - it won't be there until it is right (unlike covert ops we don't see it as important enough for the development time on this project --- cough cough...