3.2 Tornadoes and severe thunderstorms

Tornadoes and severe thunderstorms are powerful weather events that can cause widespread destruction. These phenomena form in environments with high energy and strong wind changes, often triggered by colliding air masses or other atmospheric disturbances.

Different types of tornadoes exist, from the destructive supercell tornadoes to the less intense landspouts and waterspouts. Their impacts range from loss of life and property damage to long-term economic and environmental consequences, highlighting the importance of preparedness and effective response strategies.

Atmospheric Conditions for Tornadoes and Thunderstorms

High Convective Available Potential Energy (CAPE) and Strong Wind Shear

• Tornadoes and severe thunderstorms typically form in environments with high CAPE and strong wind shear
• CAPE measures the amount of energy available for convection, influenced by air temperature and moisture content
  • Higher CAPE values indicate a greater potential for severe weather (supercell thunderstorms)
• Wind shear refers to the change in wind speed or direction with height
  • Strong vertical wind shear is crucial for the development of rotating updrafts, known as mesocyclones, which can lead to tornado formation (hook echoes on radar)

Triggering Mechanisms and Instability

• Severe thunderstorms often develop along cold fronts, where cool, dry air collides with warm, moist air, creating instability and lifting (squall lines)
• The presence of a strong jet stream can enhance upper-level divergence, which promotes rising motion and the development of severe thunderstorms
• Dry lines, which separate moist air from dry air, can also trigger severe thunderstorm development when they interact with unstable air masses (Texas and Oklahoma)
• Daytime heating and orographic lifting can also contribute to instability and thunderstorm formation (Rocky Mountains)

Tornado Types and Characteristics

Supercell and Non-Supercell Tornadoes

• Supercell tornadoes are the most common and destructive type, forming from rotating updrafts within supercell thunderstorms
  • Often have a long duration and can produce extensive damage (Joplin, Missouri in 2011)
• Landspout tornadoes are usually weaker and shorter-lived than supercell tornadoes
  • Form from non-supercell thunderstorms or cumulus clouds and are not associated with a mesocyclone (Colorado)
• Waterspouts are tornadoes that form over water, typically from non-supercell thunderstorms or cumulus clouds
  • Can move onshore and cause damage as landspout tornadoes (Florida Keys)

Tornado Subtypes and Characteristics

• Multiple-vortex tornadoes contain several smaller vortices rotating around a central axis
  • These vortices can cause more localized, intense damage within the larger tornado path (Tri-State Tornado of 1925)
• Satellite tornadoes are smaller tornadoes that form near a larger, primary tornado
  • Can be just as destructive as the main tornado and pose additional threats to life and property (Hesston, Kansas in 1990)
• Tornado intensity is measured using the Enhanced Fujita (EF) scale, which ranges from EF0 (weakest) to EF5 (strongest)
  • Wind speeds and damage potential increase with each rating (EF5 tornadoes can have wind speeds exceeding 200 mph)

Impacts of Tornadoes and Thunderstorms

Human and Property Impacts

• Tornadoes can cause fatalities and injuries due to high winds, flying debris, and structural collapse
  • The most violent tornadoes (EF4 and EF5) account for the majority of tornado-related deaths (Tuscaloosa, Alabama in 2011)
• Severe thunderstorms can produce damaging straight-line winds, large hail, and flash flooding, all of which can threaten human lives and cause injuries
• Property damage from tornadoes can be extensive, with the most violent tornadoes capable of completely destroying well-built structures
  • The cost of rebuilding after a tornado can be significant for communities (Moore, Oklahoma in 2013)
• Severe thunderstorms can cause property damage through high winds, hail, and flooding
  • Hailstones can damage roofs, windows, and vehicles, while flash flooding can inundate buildings and infrastructure (Dallas, Texas hailstorm in 2016)

Environmental and Economic Impacts

• Tornadoes and severe thunderstorms can have significant environmental impacts, such as deforestation, soil erosion, and disruption of natural habitats
• Agricultural losses can be substantial, with crops and livestock vulnerable to high winds, hail, and flooding
  • Hailstorms can devastate crop yields and cause significant economic losses for farmers (Kansas and Nebraska)
• The economic impacts of tornadoes and severe thunderstorms extend beyond direct property damage
  • Business interruptions, reduced tourism, and increased insurance premiums can affect local economies long after the event (Greensburg, Kansas in 2007)

Preparedness and Response for Tornado and Thunderstorm Events

Emergency Planning and Public Education

• Develop and maintain a comprehensive emergency plan that includes warning systems, evacuation routes, and designated shelter areas
• Conduct regular tornado drills and severe weather awareness campaigns to educate the public about the risks and appropriate actions to take during an event
  • National Weather Service's "Tornado Preparedness" and "Severe Weather Awareness Week" initiatives
• Strengthen building codes and encourage the construction of storm shelters or safe rooms in homes, schools, and public buildings
  • FEMA's "Safe Room" program and ICC/NSSA 500 standard for storm shelters

Forecasting, Warning, and Communication Systems

• Invest in advanced weather monitoring and forecasting technologies, such as Doppler radar and weather satellite systems, to improve the accuracy and lead time of severe weather warnings
  • National Weather Service's "Weather Ready Nation" initiative and upgrades to the WSR-88D radar network
• Foster collaboration between emergency management agencies, local governments, and community organizations to ensure a coordinated and effective response to severe weather events
  • FEMA's "Whole Community" approach to emergency management
• Establish a robust communication system to disseminate warnings and critical information to the public, including the use of wireless emergency alerts, social media, and traditional media outlets
  • Wireless Emergency Alerts (WEA) system and integration with smartphone apps (FEMA, Red Cross)
• Encourage individuals and families to create their own emergency plans and kits, including supplies for sheltering in place or evacuating if necessary
  • Ready.gov's "Build a Kit" and "Make a Plan" resources for personal preparedness