Thunderstorm facts and formation

• Storms are atmospheric disturbances, while thunderstorms are storms specifically with thunder and lightning
• Thunderstorms can occur almost anywhere, and severe ones can lead to tornadoes and hurricanes
• Most thunderstorms move with the wind flow in the troposphere
• Worldwide, there are about 16 million thunderstorms annually
• The United States experiences around 100,000 thunderstorms each year, with about 10% reaching severe levels

Thunderstorm Description

• Thunderstorms occur in cumulonimbus clouds, which are tall and dark
• These storms typically have strong winds and precipitation (rain, sleet, hail, snow), but sometimes have no precipitation
• An updraft causes thunderstorms, which happens when warm, moist air rises and mixes into the atmosphere
• Frequent thunderstorms form where warm air from tropical areas and cooler air from polar regions meet

Thunderstorm Formation

• Thunderstorm formation requires moisture, unstable air, and a lifting force (heat)
• The sun heats the Earth's surface, warming the air above it and causing it to rise
• Convection is the transfer of heat from the Earth's surface to the upper atmosphere
• Water vapor in the air cools, leading to condensation and the formation of cumulus clouds, and cooled air drops
• Convection cell is the cycling of rising and falling air, which is considered unstable air
• Typical thunderstorms can reach 33,000 feet, with some exceeding 66,000 feet in altitude
• Tall clouds darken and become cumulonimbus clouds
• Ice particles collide in the cloud, causing electricity to build up which causes a bolt of lightning
• Thunder is the sound waves created by lightning

Storm Formation

• Storms form due to quick upward movement of warm, moist air with a force pushing it upward
• A trough, which is a long low-pressure system, can push the cloud upwards
• As warm air rises, it cools, condenses, and forms a cumulonimbus cloud, potentially reaching over 12 miles high
• Downdrafts are cool air sinking, created by falling water droplets dragging cooler air
• The combination of warm updrafts and cool downdrafts creates a storm cell
• The process repeats until the air temperature is equalized and an anvil shape forms creating anvil head/thunderstorm clouds

Thunderstorm Life Cycle

• Thunderstorms go through three stages: developing, mature, and dissipating

The Developing Stage:

• A cumulus cloud is pushed upward by an updraft
• The cumulus cloud grows in height
• This stage has little to no precipitation but there may be lightning

The Mature Stage:

• In this stage, precipitation begins to fall out of the storm, creating a downdraft
• As the downdraft spreads, wind speed increases
• Heavy rain, hail, lightning, and tornadoes can occur
• Precipitation eventually overcomes the updraft, leading the storm to dissipate

The Dissipating Stage:

• A front forces the storm to break up, cutting off the warm, moist air supply
• Precipitation decreases, and the storm dissipates

Types of Thunderstorms

Single Cells

• Small, weak, and brief (typically lasting about an hour)
• Driven by hot temperatures on a summer afternoon
• Can contain heavy rain and lightning
• Often called "popcorn" storms

Multi-Cell Clusters

• Groups of storm cells spread out, forming from new updrafts along the edge of rain-cooled air (gust front)
• Pass through an area in 30 to 60 minutes, but can last for hours
• Can produce hail, strong winds, brief tornadoes, and flooding

Multi-Cell Lines

• Arranged in a line with high winds and heavy rain, also called a squall line
• A squall is a sudden burst of violent wind
• Pass through quickly due to their long, narrow shape
• Less likely to produce tornadoes

Supercells

• Long-lasting, organized storms that can last over an hour long
• Gaining power by an updraft that is tilted and rotating and can rotate for around 20-60 minutes
• Large and violent tornadoes can form from supercells

Severe Thunderstorms

• Classified as "severe" if containing: hail one inch or greater, winds exceeding 58 mph, or a tornado
• Can occur from any type of storm cell

Mesoscale Convection

• A system is a collection of thunderstorms acting as a system
• These systems can be very large and last longer than 12 hours
• Have a low-pressure center that pulls winds into a vortex
• The vortex can persist beyond the storm's dissipation an can become the start of the next
• If it moves over warm water, it can become the eye of a tropical storm or hurricane

Hazards

• Thunderstorms are most common in spring and summer, but can occur any time of year
• Hazards include lightning, hail, tornadoes, flash floods, downbursts, and storm asthma

Lightning:

• Produced when ice particles collide, creating electrical charges
• Electrical energy is released, heating the air and causing it to expand, which creates thunder
• Lightning is seen before thunder because light travels faster than sound

Hail:

• Chunks of ice falling from an updraft
• Can damage cars, homes, and harm animals and people

Tornadoes:

• Rapidly rotating vortices reaching the ground
• Rated by wind speed
• Very dangerous due to their rapid formation and destructive potential

Flash Floods:

• Heavy rainfall causes water to accumulate rapidly
• Can damage roads and carry away cars

Downburst:

• Powerful winds formed when high air pressure systems sink
• Sudden change in density is the downburst that is felt
• Can damage buildings, crops, and trees

Storm Asthma:

• Asthma attack triggered by a thunderstorm
• Pollen absorbs moisture and bursts into smaller particles, increasing pollen count in the air

Thunderstorms are storms characterized by thunder and lightning, typically forming in cumulonimbus clouds. They require moisture, unstable air, and a lifting force, often occurring where warm and cool air masses converge. The United States sees approximately 100,000 thunderstorms annually.