Tornadoes and Convective Storm Disasters

Definition 

Storms are disturbed states of the earth's atmosphere, manifesting as temperature, humidity, pressure, wind velocity, cloud cover, lightning, and precipitation.  

A tornado is a rapidly rotating column of air extending vertically from the surface to the base of a cloud, often with a near-surface circulating debris/dust when over land or spray when over water. A funnel cloud is often (but not always) visible and may partly or wholly extend from the cloud base to the ground.  

Convective movement (i.e., warmer parts moving up and cooler parts moving down) in the atmosphere is also known to create convective storms (i.e., thunderstorms). Convective storms are generally accompanied by lightning and thunder, usually with strong gusts of wind, heavy rain, and sometimes with hail. Thunderstorm severity is measured according to (1) the nature of the lightning and thunder, (2) the type and intensity of the precipitation, (3) the speed of gusts and sustained winds, (4) the cloud appearance, and (5) the effect on surface temperature.  

 Speed of Onset and Duration 

Whereas convective storms commonly develop over hours, tornadoes are acute onset disasters that develop within a few minutes and limit advance warning effectiveness. Both types of storms most commonly occur within a relatively short period, seldom exceeding several hours in duration. Slow-moving storms associated with high precipitation tend to cause more inland flooding that can take weeks to resolve. Full recovery from localized, severe wind damage can take months to years.  

 Consequences 

Convective storms create secondary hazards, including lightning, wildfires, inland flooding, landslides, and high wind conditions. Along with more limited warning times, the higher wind speeds of tornadoes often result in a destructive swath with multiple injuries. These incidents typically result in a relatively low number of injuries, as well as localized population displacement, and its associated loss of shelter, water, food, sanitation, hygiene, and personal safety.  

 Scale 

During the past 60 years there were 1,956 storm-related disasters reported worldwide that caused an average of 29 deaths per incident.  

Storms range in size from meters to a few kilometers (e.g., tornadoes), to a few-to-several-hundred kilometers (convective systems), and many hundreds of kilometers (extratropical cyclones). 

Tornado severity is measured according to wind speeds using a standard index known as the Enhanced Fujita scale. This scale is based on estimated wind speeds and related damage (taking into consideration how most structures are designed).