Inclement usually refers to severe or harsh weather that is cold and wet. When packing for a trip to the Caribbean bring tank tops and shorts, but don't forget a raincoat in case of inclement weather.
This adjective can also refer to a person or action that is harsh and unmerciful. Inclement is from a Latin root formed from the prefix in- "not" plus clemens "clement." This English adjective clement can mean either mild or merciful; the more commonly used noun clemency can mean mildness or mercy.