Oh the weather outside is frightful.
Waiting four hours overnight in the parking lot of a Casey’s General Store for a snow plow to come by and clear a path home certainly provides plenty of time to think about the game effects of winter weather.
Historically, winter has been the bane of warfare. While there have been notable exceptions, the general rule was that armies suspended their campaigns once the snow started falling. Even in the modern age, with machines capable of overcoming piles and piles of snow, extreme cold can bring an army to a halt. Ice has ever been treacherous.
But your game world need not be so rigid. After all, your players are heroes. What’s a little snow to them? I bet you won’t catch them waiting around for a snow plow to make things easy.
In D&D, winter conditions present a great opportunity to challenge the players’ resourcefulness, especially if your game has previously only be set in some sort of endless summer. But be warned, the trick is not to let things grind to a halt.
Exposure to cold is resolved by an Endurance check made against a target difficulty class. Severe weather is a DC 20, cold a DC 22 and frigid cold a DC 26. As for the effects of snow an ice in tactical combat, that’s a judgment call by the DM, using the modifiers from the Encounter Settings section of the DMG and Chapter 9 of the Player’s Handbook. A light or heavy snowfall might be designated as Obscured Terrain. Slippery ice might be Challenging Terrain. Drifting snow and deep snow banks could be considered Hindering Terrain if you try to move through it, Cover Terrain if you hide behind it. If it’s a mountain of snow and ice that blocks your way, say a glacier or an avalanche, maybe it’s Blocking Terrain. Accumulated snow, say ankle-to-knee deep, might only be classified as Difficult Terrain, and slow movement by 1 square.
Exposure depends on what clothes your PC is wearing. Basically, though, unprotected creatures must succeed on a Fortitude save against a DC 15 (+1 per previous check) each hour or suffer 1d6 points of nonlethal damage. Sleet and snow both cut visibility in half, applying a -4 penalty to Search and Spot checks. Ranged attacks take a -4 penalty. Snowstorms impose -8 penalties in these cases. Snow impedes movement based on depth of the snow cover. Medium creatures have to pay 2 squares of movement if snow is less than 2 feet deep and 4 squares of movement if it’s deeper than that. If the depth is greater than 5 feet, a DC 5 Strength or Balance check is required.
Regardless of system, don’t be a slave to the rules, especially when dealing with weather conditions. In my opinion, it’s the most difficult thing to simulate. Use your sense of story, gauge carefully the PCs capabilities, and adjust as need be, such as:
> Try not to use weather conditions as a means of punishing players. Rather, make it part of the atmosphere, heightening the adventure. If you can, try not to let the players lose their fingers and toes to frostbite, if you can help it. (NPCs are fair game, of course).
> Occasionally, weather can steer the story. Remember when the fellowship of the ring must take a detour when a blizzard blocks Redhorn Pass?
> Mostly, though, use snow and ice as challenges to be overcome. They’re like traps, in a sense, which must be defeated bypassed, as the players see fit.
> Use wintry weather for the sake of atmosphere. Maybe it’s enough to know that the blizzard rages outside, while the dwarven hearth-fires offer warmth and comfort.
I’d love to hear about your in-game experiences with snow and ice, and whether you thought it heightened or ruined the play experience.