Rainstorm refers to the heavy rainfall with precipitation exceeding several millimeters within 24 hours, which is called rainstorm.

Heavy rainfall with 24-hour precipitation exceeding 50 mm is called "rainstorm". According to its precipitation intensity, it is divided into three grades, namely, 24-hour precipitation of 50-99.9 mm is called "rainstorm", 100-249.9 mm is called "heavy rainstorm", and more than 250 mm is called "extraordinary rainstorm".

Heavy rain refers to rain with high precipitation intensity, which is often formed in cumulonimbus clouds. The formation process of rainstorm is quite complicated. Generally speaking, sufficient and continuous water vapor, strong and lasting upward movement of airflow and instability of atmospheric structure are the main physical conditions for heavy rain. The favorable combination of various scales of weather system and underlying surface, especially topography, can produce heavy rain.