So theres a few weather effects in game already. (Sunny, Cloudy, Rain, Acid Rain,etc) but I think a few more could be interesting to see in game. Maybe after the first few seasons.
Snow - Winter only (I dont know if this is in game already. Never really survived long enough)
Creates snow piles when shallow and snow drifts when deep. Melts away in sunlight. Cools your feet and legs in drifts, only feet in piles.
Radiation Storms - Clouds of radiation drift randomly across the map. About the size of average towns. Form anywhere on the map dissipate after a few days.
Twister- Thin concentrated towers of wind that drift across the map. Might not even see them, only one or 2 per storm.
Fire Rain - Spatterings of burning oil and gasoline fall on the map like acid rain, but the gaps in between are greater. Maybe have it so the fire rain cannot burn buildings and only lasts a few mins.
Hail - Winter, autumn and early spring. Hurts and cools head, and torso if outside too long.
Junk hail - random objects fall from the sky, mostly bottles and other smashables. Hurt player on impact, shatter on ground. rarely drop useful items like weapons, but will be damaged as if corroded by acid.
If I think of more I will update. Hope these are added or modded in. It sounds like it could be an extra level of challenge.