Severe Weather Flashcards

Vocabulary flashcards covering fundamental definitions, classifications, and processes related to severe weather, thunderstorms, and tornadoes.

Thunderstorm

A storm defined specifically by the presence of lightning and thunder.

Cumulus Stage

The initial stage of a thunderstorm's lifecycle, during which an air parcel is forced to rise, cool, and condense into a cumulus cloud.

Entrainment

The process by which downdrafts pull cold, dry air from outside a cloud toward the ground.

Mature Stage

The second and most intense stage of a thunderstorm lifecycle, characterized by coexisting updrafts and downdrafts, heavy precipitation, and strong gusty winds.

Dissipating Stage

The final stage of a thunderstorm lifecycle, occurring when downdrafts overtake updrafts, cutting off latent heat and causing the storm to weaken.

Air Mass Thunderstorms

Also called ordinary thunderstorms, these follow a standard three-stage lifecycle and are triggered by localized uplift within a warm, moist ($mT$) air mass.

Outflow Boundary (Gust Front)

An arc-shaped boundary created when thunderstorm downdrafts slam into the ground and spread outward, acting as a mini-cold front that can trigger new cumulus cloud growth.

Multi-Cell Thunderstorms

Complex storm systems lasting several hours that consist of multiple thunderstorms in various stages of development sustained by outflow boundaries.

Severe Thunderstorm

A thunderstorm classified by the Storm Prediction Center as having wind speeds exceeding $58\text{ mph}$ or producing hail with a diameter of at least $1.9\text{ cm}$.

Squall Line

A linear arrangement of thunderstorms that develops over hundreds of miles along the leading edge of a gust front or dryline.

Dryline

A boundary where a dry, warm continental tropical ($cT$) air mass penetrates between a maritime tropical ($mT$) and continental polar ($cP$) air mass, causing severe air lifting.

Supercell

A highly powerful single-cell thunderstorm that can reach heights of $65,000\text{ ft}$, last several hours in the mature stage, generate winds over $100\text{ mph}$, and spawn most tornadoes.

Mesocyclone

A vertically rotating column of air within a thunderstorm formed when strong updrafts lift horizontal wind shear.

Wall Cloud

A rotating cloud feature that extends below the base of a thunderstorm from a mesocyclone.

Stepped Leader

A zigzag pathway of negative charges moving from the base of a cloud down toward the ground.

Return Stroke

The visible electrical discharge that flows upward from the ground toward a cloud along the path created by a stepped leader.

Thunder

A shockwave created when air superheated by lightning expands violently.

Dry Thunderstorms

Thunderstorms that generate lightning but little to no surface rain because precipitation evaporates in dry air before reaching the ground.

Hail

Precipitation consisting of ice pellets formed in cumulonimbus clouds as updrafts repeatedly carry them above and below the atmospheric freezing level.

Flash Flood

A short-term event featuring a rapid stream rise that occurs within $6\text{ hours}$ (often within $2\text{ hours}$) of heavy rainfall, dam breaks, or rapid snowmelt.

Microburst

A intense downburst where evaporating moisture cools falling air, making it denser and causing it to blast laterally across the ground at speeds up to $100\text{ mph}$.

Tornado

A violently rotating column of air descending from a thunderstorm and in physical contact with the ground.

Tornado Alley

A region in the United States Midwest where cold polar air from Canada collides with warm subtropical air from the Gulf of Mexico, resulting in frequent tornado activity.

Enhanced Fujita Scale

An updated tornado classification system implemented in February 2007 that rates tornadoes from $0$ to $5$ based on structural and vegetation damage assessments to estimate wind speed.

Suction Vortices

Smaller, distinct rotating columns of air contained within certain large, intense multiple-vortex tornadoes.

Tornado Watch

An alert issued by the Storm Prediction Center informing the public that atmospheric conditions are favorable for tornado formation in a given area and timeframe.

Tornado Warning

An alert issued by the National Weather Service when a tornado has been sighted or detected, signaling a high probability of imminent danger.

Vortex2

The largest field project of scientists dedicated to monitoring and studying tornadoes, funded by the National Science Foundation (NSF) and NOAA.