"Severe weather phenomena are weather conditions that are hazardous to human life and property. Severe weather can occur under a variety of situations, but three characteristics are generally needed: a temperature or moisture boundary, moisture, and (in the event of severe, precipitation-based events) instability in the atmosphere. (Wikipedia)
National Weather Service - "Our mission: Provide weather, water, and climate data, forecasts and warnings for the protection of life and property and enhancement of the national economy."