Sometimes rain will be falling on a chosen location, the rate at which this occurs is seemingly random.
More than sceneric, rain has a considerable effect on gameplay, and it can make certain missions easier or more difficult.
Vision range Edit
The vision range of both players and NPCs is reduced while raining. While this often helps the player, as it makes it more difficult for enemies to spot them, it also makes it more difficult for players to see enemies from afar. This is especially troublesome against enemy ninjas like the Mosu or Kenobi, already stealthy in their normal attire, receive additional concealment during rain. On a lesser note, rain also makes light sources less visible.
Slippery ground Edit
The ground becomes slippery during rain. Players are not much affected while running at normal speed, but if they sprint (by pressing "O") it becomes difficult to control the direction of the run, make turns or stop, and very easy to slip and fall from ledges. Enemies are also affected by the slippery ground, having the same difficulty as the player if they run faster and often tripping.
Sound reach Edit
Because of the splashes of falling rain, sound reach becomes lower. Bells, explosions, yelling, dog barking and impacts are muffled and harder for the enemy to hear, giving the player an advantage. This effect is not absolute however, and nearby enemies may still hear the sounds.