Severe weather encompasses dangerous meteorological phenomena—such as high winds, hail, tornadoes, and tropical cyclones—that pose risks to life and property, and it is a rare subset of extreme weather. The World Meteorological Organization splits it into general severe weather (e.g., nor'easters) and localized severe weather (e.g., downbursts and tornadoes), which typically form from thunderstorms under conditions of moisture, lift, and instability. Supercell thunderstorms generate the most severe hail and tornadoes, while bow echoes produce destructive straight-line winds. Meteorologists classify severe thunderstorms into three tiers—approaching severe, severe, and significantly severe—based on hail diameter and wind speed, with the latter two triggering official warnings from agencies like the US National Weather Service. Notably, climate change is increasing the frequency and intensity of some extreme events, including heatwaves and droughts.