Severe Weather: Thunderstorms, Lightning, and Tornadoes

A comprehensive vocabulary flashcard set defining the key atmospheric concepts, formation stages, and specialized terms related to thunderstorms, lightning phenomena, and tornadoes.

Thunderstorm (T-storm)

A cumulus cloud producing lightning and thunder, indicating great vertical development and atmospheric instability, with an average duration of $1\text{--}3\,\text{hours}$ (or up to $12\,\text{hours}$ or more).

Cumulus Stage

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

Entrainment

An influx of cool, dry surrounding air into a thunderstorm that helps fuel downdrafts during the mature stage.

Mature Stage

The thunderstorm stage initiated when falling raindrops start downdrafts, further fueled by entrainment, producing heavy rains.

Dissipating Stage

The final thunderstorm stage that occurs as rainfall decreases due to the loss of warm, moist air and latent heat energy, causing the storm to break up and the cloud to evaporate.

Derecho

A widespread, strong linear or "straight-line" wind event classified when winds exceed $58\,\text{mph}$, capable of exceeding $100\,\text{mph}$ ($128\,\text{mph}$ record), and occurring predominantly from May to August in the Upper Midwest.

Microburst

A small (less than $2\,\text{mi}$ in diameter), severe downburst produced by a thunderstorm whose intense wind shear can damage aircraft or cause crashes.

Lightning

Flashes of light generated by charge separation within a developing thunderstorm, which discharges the negative base of the cloud by transferring positive charges to the base and negative charges to the top.

Step Leader

An invisible pathway of charges that establishes from the cloud base toward the ground in multiple linked branches during a cloud-to-ground lightning strike.

Return Stroke

The rapid movement of opposite charges traveling back toward the cloud once a path touches ground, creating the illuminated visible flash of lightning.

Ball Lightning

A lightning phenomenon that appears as a round, glowing mass of electrified air, typically basketball-sized or smaller, and lasting around $15\,\text{seconds}$.

St. Elmo's Fire

A luminous electrical discharge resulting from atmospheric ionization.

Sprites

Large, short-lived electrical discharges that can resemble giant red jellyfish and occur up to $57\,\text{miles}$ above cloud tops.

Blue Jets

Upward electrical discharges moving at approximately $60\,\text{mph}$ that reach heights of up to $30\,\text{miles}$ above the surface.

Thunder

The sound emitted when lightning heats the surrounding air to between $15{,}000^\circ\text{C}$ and $33{,}000^\circ\text{C}$ in milliseconds, traveling at the speed of sound ($1082\,\text{feet/sec}$, or about $5\,\text{seconds}$ per mile).

Tornado

A violently rotating column of air extending downward from a cumulonimbus cloud in response to extremely low central air pressure ($90\text{--}100\,\text{mb}$ below surrounding air), producing winds upwards of $300\,\text{mph}$.

Enhanced Fujita Scale

A modified version of Dr. Ted Fujita's original scale used to measure tornado wind speeds, ranging from EF0 ($65\text{--}85\,\text{mph}$) to EF5 (winds $> 200\,\text{mph}$).

Mesocyclone

A rotating column of air created when vertical wind shear causes air near the ground to roll like a barrel, which is drawn upward by updrafts to generate strong tornadoes (EF3 to EF5).

Severe Weather Watch

An advisory issued to indicate that atmospheric conditions are favorable for the development of severe thunderstorms or tornadoes.

Severe Weather Warning

An advisory issued to indicate that a severe storm or tornado is currently occurring, observed, or imminent in the area.