Flame Storm
Eldritch Storm
Sooty thunderclouds shot through with red and orange lightning release a deluge of fiery droplets. Any creature caught in the burning rain takes 2d6 fire damage at the start of each of its turns. The droplets ignite any flammable objects that aren’t being worn or carried; otherwise, the droplets burn out immediately. The smoke, soot, crackle, and low roar of the storm impose disadvantage on Wisdom (Perception) checks and ranged attack rolls.
A flame storm usually lasts 2d4 minutes, though the originating storm clouds can persist for days, creating multiple flame storms.
Source: Tasha’s Cauldron of Everything p. 163