Mechwarrior 5's weather effects and night-fights can leave a little to be desired, with night not always requiring night vision and the weather little more than cosmetic tweaks. It's more arcade experience than realistic weather effects. For those who like a little more simulator in their mech sim modder RainingFire416 has cooked up the Weather Improvement Mod.
Weather Improvement Mod tweaks the game's weather settings so you'll actually care about time of day and conditions when accepting a contract. Harsh weather is now realistically harsh, with extreme snows giving a whiteout blizzard effect. Night missions are also appropriately dark, and making use of night vision in combat is no longer optional. In addition, the mod adds daytime missions to volcanic biomes and nighttime missions for the iron oxide and sulfurous biomes. Finally, there are also crystal-clear weather days, where barely any haze obscures long-distance views.
Despite its flaws, the bones of Mechwarrior 5 were quite good on release. At the time, I said that "The big campaign map is really just a vehicle for a simple, tight, and effective loop: travel to a new conflict zone, pick a mission and ruin your mechs in combat, find a sidequest to accept, head to some industrial worlds to rearm and repair, then head back out to your new mission." It's the combat that makes the game worth playing, so I'm glad to see modders expanding the experience for those of us who like a realistic simulator.
You can find the Weather Improvement Mod over at Nexusmods.