Thunderstorms, Lightning, and Tornadoes

Vocabulary flashcards covering the characteristics, stages, mechanisms, and associated phenomena of thunderstorms, lightning, and tornadoes based on lecture notes.

Thunderstorm

A cumulus cloud that produces the characteristic events of lightning and thunder, lasting on average $1-3\,\text{hours}$ but capable of lasting up to $12\,\text{hours}$ or more.

Cumulus Stage

The initial build-up stage of cumulus clouds fueled by updrafts (up to $160\,\text{kph}$) of warm, moist air cooling adiabatically.

Mature Stage

The thunderstorm stage in which raindrops begin to fall, initiating downdrafts that are fueled by the influx of cool, dry air.

Entrainment

The process involving an influx of cool, dry surrounding air into a thunderstorm that helps to fuel downdrafts.

Dissipating Stage

The final stage of a thunderstorm that occurs as the rate and amount of rain lessens with the loss of warm, moist air and latent heat energy, causing the cloud mass to break up and evaporate.

Derecho

Strong linear or "straight-line" winds exceeding $58\,\text{mph}$, capable of exceeding speeds of $100\,\text{mph}$ with a recorded high of $128\,\text{mph}$.

Microburst

A small, severe downburst less than $2\,\text{mi}$ in diameter produced by thunderstorms, with wind shear capable of damaging or crashing aircraft.

Lightning

Flashes of light resulting from a build-up of millions or hundreds of millions of separated positive and negative charges in a cloud discharging to restore balance.

Step Leader

An invisible pathway of charges formed from the cloud base toward the ground, marking the first step of a cloud-to-ground lightning strike.

Return Stroke

The movement of opposite charges back cloudward that illuminates the pathways and causes the visible flash of lightning.

Ball Lightning

A form of lightning that appears as a round, glowing mass of electrified air, usually of basketball size or smaller, lasting around $15\,\text{seconds}$.

St. Elmo’s Fire

A luminous atmospheric electrical phenomenon that occurs as the result of ionization.

Sprites

Large but short-lived electrical phenomena that can resemble giant red jellyfish and reach heights of up to $57\,\text{miles}$ above the cloud top.

Blue Jets

Upward electrical discharges moving at about $60\,\text{mph}$ that attain heights of $30\,\text{miles}$ above the surface.

Thunder

The sound emitted when a lightning flash heats surrounding air to between $15{,}000^\circ\text{C}$ and $33{,}000^\circ\text{C}$ in milliseconds, traveling at a speed of about $1082\,\text{feet/sec}$.

Tornado

A violently rotating vortex extending downward from a cumulonimbus cloud, characterized by central barometric pressures upwards of $90 - 100\,\text{mb}$ below surrounding air and winds upwards of $300\,\text{mph}$.

Enhanced Fujita Scale

A modified wind rating scale originally developed by Dr. Ted Fujita, classifying tornadoes from EF0 ($65-85\,\text{mph}$) up to EF5 (winds $> 200\,\text{mph}$).

Mesocyclone

A rotating column of air formed in stronger tornadoes (EF3 to EF5) when tumbling, barrel-rolling surface air is drawn up into the thunderstorm.

Upper-Level Support

Wind flow aloft, usually provided by the jet stream, that pulls away rising air to promote greater surface uplift during tornado formation.