so, I was reading "freezing weapons" topic, and through that not only freezing weapons could decrease temperature (may be below zero), but also weather.
I remember BattleTech books; one of them depicts two clan warriors having mech duel in cold area; mech started to be quite cold before warming up due to engine and weapons heating. When one of warrior shut down her mech (to hide from enemy), after short time her mech's legs was stick frozen to the land.
basically this gave me idea of weather conditions - modifications for the field. Like old plates (one with +damage, null resist ect.), however, plates only was working on a single tile and could favor only one mech and not both (diamond shell vs god mode, guess who would win with 4 null resist plates on the field :)). Weather is a condition that works on all mechs on the field, and has small effect of some sort, thus it isn't that unfair. Best example of such a weather is Blizzard, which cools down and freezes all mechs rapidly. Notably, cooling by blizzard deals damage, unlike manual cooling.
Not only actual weather, but other ways to modify map could be implemented. Based on map, different effects are active.