☁️Meteorology Unit 10 – Thunderstorms and Tornadoes

Key Concepts and Definitions

• Thunderstorms are convective storms characterized by the presence of lightning and thunder
• Tornadoes are violently rotating columns of air extending from a thunderstorm to the ground
• Supercell thunderstorms are highly organized, long-lived storms with a rotating updraft (mesocyclone)
• Squall lines are elongated lines of thunderstorms that can produce severe weather
• Downbursts are strong downdrafts that cause damaging winds at the surface
  • Microbursts are small-scale downbursts less than 4 km in diameter
  • Macrobursts are large-scale downbursts greater than 4 km in diameter
• Fujita scale (F-scale) and Enhanced Fujita scale (EF-scale) are used to rate tornado intensity based on damage

Formation and Development

• Thunderstorms form when three conditions are met: moisture, instability, and a lifting mechanism
• Moisture is necessary for the formation of clouds and precipitation
• Instability occurs when warm, moist air near the surface rises rapidly due to being less dense than the surrounding air
• Lifting mechanisms include frontal boundaries, convective heating, and orographic lifting
  • Frontal boundaries are the interfaces between air masses of different densities
  • Convective heating occurs when the sun heats the Earth's surface, causing air to rise
  • Orographic lifting happens when air is forced to rise over mountains or other topographical features
• Tornadoes typically form within supercell thunderstorms when strong wind shear and rotation are present
• Wind shear is the change in wind speed or direction with height, which can cause horizontal rotation in the atmosphere

Structure and Characteristics

• Thunderstorms have three main stages: cumulus, mature, and dissipating
  • Cumulus stage is characterized by updrafts and the formation of a cumulus cloud
  • Mature stage features both updrafts and downdrafts, as well as heavy precipitation, lightning, and possibly severe weather
  • Dissipating stage occurs when downdrafts dominate, and the storm gradually weakens
• Supercell thunderstorms have a rotating updraft (mesocyclone) and can produce severe weather such as large hail, strong winds, and tornadoes
• Tornadoes have a central region of low pressure called the eye, surrounded by the eyewall, where the strongest winds occur
• Tornado vortex signature (TVS) is a radar signature indicating the presence of a tornado
• Wall cloud is a lowering of the cloud base in a supercell thunderstorm, often associated with tornado development

Types and Classification

• Single-cell thunderstorms are short-lived, isolated storms that typically do not produce severe weather
• Multi-cell thunderstorms are clusters of storms that can produce severe weather and have a longer lifespan than single-cell storms
• Supercell thunderstorms are the most severe type, capable of producing significant severe weather events
• Tornadoes are classified using the Fujita scale (F-scale) or Enhanced Fujita scale (EF-scale) based on the damage they cause
  • EF0: wind speeds of 65-85 mph
  • EF1: wind speeds of 86-110 mph
  • EF2: wind speeds of 111-135 mph
  • EF3: wind speeds of 136-165 mph
  • EF4: wind speeds of 166-200 mph
  • EF5: wind speeds greater than 200 mph
• Waterspouts are tornadoes that form over water, typically less intense than land-based tornadoes

Detection and Forecasting

• Radar is the primary tool for detecting and tracking thunderstorms and tornadoes
  • Doppler radar measures the velocity and direction of wind, helping to identify rotation within storms
• Satellite imagery is used to monitor the development and movement of thunderstorms on a larger scale
• Skywarn is a network of trained volunteer weather spotters who report severe weather to the National Weather Service
• Numerical weather prediction models are used to forecast the potential for thunderstorm and tornado development
• Severe weather watches are issued when conditions are favorable for severe weather, while warnings are issued when severe weather is imminent or occurring

Safety and Preparedness

• Develop a severe weather plan and identify safe locations to shelter during a thunderstorm or tornado
• Safe locations include interior rooms on the lowest floor of a building, away from windows and exterior walls
• Avoid mobile homes, vehicles, and open spaces during severe weather events
• Monitor weather forecasts and stay informed about potential severe weather threats
  • NOAA Weather Radio provides continuous weather information and alerts
• If caught outdoors during a thunderstorm, seek shelter in a substantial building or a hard-topped vehicle
• If caught outdoors during a tornado, seek shelter in a sturdy structure or lie flat in a nearby ditch or low-lying area

Environmental Impact

• Thunderstorms and tornadoes can cause significant damage to buildings, infrastructure, and natural environments
• Strong winds associated with thunderstorms and tornadoes can uproot trees, damage crops, and cause power outages
• Heavy rainfall from thunderstorms can lead to flash flooding, erosion, and landslides
• Lightning strikes can ignite wildfires, particularly in dry, forested areas
• Hail produced by thunderstorms can damage crops, vehicles, and buildings
• Tornadoes can cause catastrophic damage, destroying homes, businesses, and entire communities

Notable Historical Events

• Tri-State Tornado (1925): The deadliest tornado in U.S. history, killing 695 people across Missouri, Illinois, and Indiana
• Super Outbreak (1974): A series of 148 tornadoes across 13 states, resulting in 319 deaths and extensive damage
• Plainfield Tornado (1990): An F5 tornado that struck Plainfield, Illinois, causing 29 deaths and $165 million in damage
• Moore, Oklahoma Tornado (1999): An F5 tornado that caused 36 deaths and $1 billion in damage
• Joplin, Missouri Tornado (2011): An EF5 tornado that killed 158 people and caused $2.8 billion in damage
• El Reno, Oklahoma Tornado (2013): The widest tornado on record, with a maximum width of 2.6 miles (4.2 km)