The nature of Rain in Ciel

As Ciel floats above the clouds, the way the islands experience rain is notably different from the surface world. Rather than coming from above, rain comes from below; during rainstorms, the clouds surge up like a rising tide as cumulonimbus towers form. Islands that are lower in elevation experience more rain more frequently. The elevation of the islands is as follows, starting from lowest/most rain to highest/least rain:

• Sky's Edge (lowest, most rain, storms)
• Verdan
• Port Solaris
• Aria
• Splinter Mountain
• Pillar Islands
• An Domhan (highest, almost no rain)

Manifestation

Since the island becomes "submerged" in the cloud during a storm, rainfall surrounds and is always accompanied by a thick fog that impedes vision and leaves belongings and clothing damp (Maximum visibility of 100ft).
Thunderstorms become especially dangerous, as the fog becomes charged with electricity. Most settlements have installed lightning rods or magic systems to control this natural phenomenon, or even turn it into energy. However, if outside of such a settlement during a thunderstorm, there is no such protection.
Once per round during a thunderstorm, the DM may roll a d20; on an 11-20, nothing happens. On a 10 or lower, characters must make a DC 10 dexterity saving throw or take 1d6 lightning damage from the storm. If a character is equipped with a metal weapon or armour, make the dexterity saving throw with disadvantage.
If occurring outside of combat turn, the DM can make a single d20 roll to represent the entire storm, only requiring one saving throw from each player.

Type

Natural