| martin skullerud |
Personally? I'd say: Demogorgon is Lord of Gaping Maw, he is the undisputed master of the whole layer. So the weather works at his whim, as though the whole place were covered with constant Control Weather at his caster level (it can be dispelled, but he can reinstate the effect as a free action on his turn). Thus, the weather conditions in any given place will be set up to favor his troops, or at the very least, punish the intruders as much as possible. For example, on the shore you could have a roaring windstorm that makes flight practically impossible, forcing PCs to navigate the mine-fields and making ranged attacks hard. In the jungle, you could have a savage rainstorm, making ground slick and sight bad. (Or a dry lightning storm that starts a forest fire). Since it's the abyss, you could also use more flashy effects: Call Lightning Storms, Evil Weather, Ice Storm and Sleet Storm effects, outright Whirlwinds -maybe even a Storm of Vengeance or two, or the occasional Earthquake.
Since, presumably, this takes some attention for Demogorgon to pull off, it would be fair to let the PCs exploit that in furthering the "distract Demogorgon in as many ways as possible" tactic -say, if they successfully dispel the Control Weather effect, that counts as an instance of distraction, which adds negative levels, in case they haven't fulfilled all the possible conditions.