Heart of the Storm is a set two Storm Sorcery Sorcerer passive features that create a storm that deals half your Sorcerer level, rounded down, when you cast a lightning or thunder spell.
Description
When you cast a Spell of Level 1 or higher that deals Lightning or Thunder damage, you cause a small, local storm. All enemies within
6 m / 20 ft take (Sorcerer Level / 2) 
Lightning damage
or Lightning damage (Sorcerer Level / 2) 
Thunder damage
.
Thunder damage How to learn
Classes:
- Class level 6: Sorcerer