Tornado Flashcards
What 3 things do thunderstorms require?
Moisture, instability, and a lifting mechanism
Describe air mass thunderstorms
- are they localized or complex
- are they destructive
- are they single or multiple celled
Contained within air masses, away from frontal boundaries.
- localized and lasts less than an hour
- most common and least destructive
- single cell storms
What are the most common thunderstorms?
Air mass thunderstorms are the most common and least destructive
What are the 3 stages of an air mass thunderstorm?
- Development stage: warm, unstable air rises, cools adiabatically and forms cumulus clouds.
- Entrainment: unsaturated dry air comes in and reduces droplet size on the edges of the cloud - The mature stage (most dangerous stage):
- Heavy precipitation drags air toward the surface as downdrafts.
- The air is cooled by evaporation of rain droplets, intensifying the downdraft.
- updrafts dominate within the cloud and downdrafts dominate the outside - Dissipative stage: Downdrafts occupy an increasing portion of the cloud base and cut off the supply of additional water
During an air mass thunderstorm, how is the air cooled
Evaporation of rain droplets, which intensifies the downdraft
Why do air mass thunderstorms occur?
warm, moist and unstable air in the atmosphere
During an air mass thunderstorm, where does the entrainment occur?
Edges of the cloud
- Unsaturated air cools the edges of the cloud by rain drops evaporating
what 4 criteria classify a severe thunderstorm?
- wind speeds exceeding 93 km/h
- not localized
- Hailstones larger than 1.9cm
- composed of several thunderstorms
What do severe thunderstorms require?
- wind shear: changes in wind speed and direction with elevation prevents the downdrafts from ‘choking’ the cloud
- high water vapour content in the lower troposphere
- uplift mechanism
Severe thunderstorms appear in groups of individual storms clustered together in ___?
Mesoscale convective systems: The shape of this group can either be:
- Linear: squall line thunderstorms
- Circular mesoscale convective complexes
What is the difference between squall line and mesoscale convective complex thunderstorms?
Squall line thunderstorms are linear
Mesoscale convective complexes are circular
How do mesoscale convective systems work?
One cell is responsible for the formation of others.
- As the first cell matures, it is carried downstream by the upper-level winds and a new cell forms upwind of the previous cell to take its place.
- the precipitation from each cell creates a downdraft which is enhanced by the cooling of the air as the rain evaporates and consumes latent heat
- upon hitting the ground, the downdrafts spread outward and converge with the warmer surrounding air to form an outflow boundary
What is an outflow boundary?
Separates thunderstorms cooled air (outflow from downdrafts) from the surrounding air
Shelf clouds are also called? How are they formed?
arcus clouds - formed by the uplift/downdraft of warm air pushed up by a gust front
other than shelf clouds, whats the other type of arcus cloud?
roll cloud - completely detached from other clouds, they roll about a horizontal axis
A supercell storm consists of what? What type of wind does it have?
a single extremely powerful cell
The updraft and downdraft bend and wrap around each other due to strong wind shear
Which storms are responsible for the significant tornados and larger hailstorms
Supercell storms
- its a single storm, not a series of storms and brings large-scale rotations with it
What are the most distinguishable factors of a supercell. If a tornado forms from a supercell, it comes from the ___?
- Vault looks like an area of no rain on a Doppler image
- Hook designates an area of intense rain and cloud rotation. Tornado forms from the hook
What’s a doppler radar
Records precipitation density using electromagnetic waves. It can also record wind speed and direction
- It emits electromagnetic waves at wavelengths that are reflected by cloud constituents
Tornados form from a ___ storm?
Supercell
What are mesocyclones? How do they form?
- Slow horizontal rotation of a large segment of the cloud deep within the cloud interior
- Form during wind shearing, and form a tornado
The mesocyclone intensifies by ___?
Narrowing - the rotating air stretches downward, and a portion of the cloud base protrudes downward to form a wall cloud
where do wall clouds form
where cool, humid air from a zone of precipitation is drawn into the updraft feeding the main cloud
- the cool, humid air condenses before the air feeding into the rest of the cloud
Whats a wall cloud
a protruding area of cloud with intense rotation associated with large hail and rain
