Weather is always a cool aspect to cram in with the rest of the things that make a game/mod yummy. It would be interesting if the weather could be randomized. I doubt that this is possible, but if not you could have two versions of a map where you use the same terrain, but the weather is different.

First approach:
So lets say you're playing Hoth. It's a bright, crisp day with not a hint of a cloud in the sky. A few hours later after some serious hardcore gameing you end up back on Hoth, only this time you're fighting in the middle of a blizzard. It would be the same map, but it would have to be played differently according to the weather conditions.

Second approach:
Of course, if you can't randomizethe weather, you could have "Day" scenarios. If any of you played Desert Combat for Battlefield 1942, you'd know that quite a few of the maps are labeled like "El Alamein Day 1, El alamein Day 2" etc.... where the number and types of vehicles are different. So if this was done for FS, Hoth Day 1 could be the clear weather scenario, while Day 2 could be the blizzard scenario.
An advantage to this approach would be that in the early releases where there are not very many maps, it would give people more battlegrounds to fight on. So instead of having for example 4 maps for the first release, you would actually have 8 or more due to weather situations.

Just my two cents.