I really love the "overloaded encounter die" mechanic described by Necropraxis.
In particular, I think the entry for "Locality" (if used in the outdoors "weather") is a great way to further add personality to a dungeon. But what would typical "vanilla D&D dungeon weather" be?
I say "vanilla" because I guess it helps me think about what are the typical environmental changes I would want in a dungeon and what are typical dungeon PC actions complicated by this change (or helping; after all some days are sunny). It also reinforces the idea of the mythic underworld; the dungeon as a being unto itself. Here is my list:
DUNGEON WEATHER (d10)
1 | SLAM! All doors slam shut; 3-in-6 if staked; all doors now a flat 1-in-6 to open
2 | FOG: A gray fog rises from the floor, ankle to knee height, obscuring the ground; -1 to detect traps
3 | SLIME BLOOMS: Green slime oozes from the ceiling on all hallways leading from the current room
4 | DUNGEON RIME: Armor ages unnaturally; -1 AC to non-magical armor & shields
5 | DARKNESS EXPANDS: All light operates at 1/2 strength
6 | SHADOW of DEATH: -1 to all Save rolls
7 | SPONTANEOUS GENERATION: Each PC roll d10; 5+ rations are spoiled by maggots
8 | ALTERED PERCEPTION: Secret doors +1 to locate
9 | EUPHORIC SPOOR RELEASE: +1 to all rxn encounter checks; divination/illusion spells enhanced
0 | TOO STILL: Dungeon weather effect ends
Of course, if your dungeon has a strong theme, I think it better to tailor the above list to fit the aesthetics.