Instant Rain
Instant Rain is an instant potion effect that changes the weather to rain.
Brewing
A Potion of Rain Calling can be brewed from an Awkward Potion using a Heart of the Sea. It cannot be turned into a splash potion, a lingering potion, or a tipped arrow.
Effects
When a player drinks a Potion of Rain Calling, they are struck by lightning and given the Darkness effect for five seconds. After that, the weather in the Overworld is changed to rain (not a thunderstorm).