Thunderstorms

Question 1

What is required for a thunderstorm to form?

Answer 1

• Instability throughout significant height
• Moisture
• Trigger for uplift
• Limited windshear

Question 2

What are some of the main risks of a thunderstorm?

Answer 2

Icing Turbulence
Hail Lightning
Pressure variation Micro/macro bursts
Water ingestion Tornadoes

Question 3

What are the 5 types of thunderstorm formation?

Answer 3

Heat/Thermal 
Air mass
Frontal 
Squall line
Orographic

Question 4

How does a heat/thermal thunderstorm form?

Answer 4

Absolute Instability occurs due to ELR being much greater than DALR
This creates a large gap of instability, where the storm forms

Question 5

How does an Air mass thunderstorm form?

Answer 5

A cold air mass moving over a warm surface, results in the warm air being underneath the cold air
This creates a deep layer of instability, due to the very steep ELR - resulting in a storm developing (alike to Thermal thunderstorms)

Question 6

How does a frontal thunderstorm form?

Answer 6

The bottom/front of a cold front rolls underneath itself (due to friction), trapping a pocket of warm air beneath it.
This warm air then rising through the cold air, great ELR, therefore instability and a storm grows.

Question 7

How does a Squall line thunderstorm form?

Answer 7

Squalls occur just ahead of a cold front, and can several hundred miles long.
Common over large continent areas (such as North America)

They are essentially many frontal thunderstorms together

Question 8

How does an Orographic thunderstorm form?

Answer 8

When conditionally unstable air is lifted at a ridge/coast

Warm air is pushed up within cold air - creating instability, therefore forming a storm.

Question 9

What are the 3 stages of thunderstorm development?

Answer 9

1- Initial/Developing/Cumulus

2 - Mature

3 - Dissipating

Question 10

What occurs during the developing stage of a thunderstorm?

Answer 10

Updraughts of 60kt (30 m/s OR 6000ft/min) within the cloud
Lasts for 15-30 minutes
No precipitation

Question 11

What occurs during the mature stage of a thunderstorm?

Answer 11

Updraughts of 10,000ft/min - and Downdraughts of 2,000ft/min
Heavy showers begun to fall
May last 30 minutes

An Anvil may also develop
There is a static build up, with lightning between -10 and 10°C
May form Micro/Macrobursts

Question 12

What occurs during the dissipating stage of a thunderstorm?

Answer 12

Downdraughts occur across the cloud
Distinct anvil forms, and can spread to become ST/AS
Can feed moisture into nearby systems
Evap. draws latent heat from falling air

Lasts 90-150 mins

Question 13

What is a Supercell storm?

Answer 13

A single very large storm.
Downdraughts occur next to the updraughts - without interfering
Which allows the storm to continue to grow.

Question 14

What are Mesoscale Convective Clusters, and where do they occur?

Answer 14

Groups of cub development, mostly along the Equatorial trough
Can cover an area of 100-1000km, lasting 1-2 days
May develop into Tropical Storms

Question 15

Why is it difficult to measure the true extent of a storm formation, using radar?

Answer 15

Radar only returns from water droplets.
Therefore giving the best reading at the base, and melting/freezing point (0°C) of a cloud

The rest of the cloud gives minimal return.

Question 16

What is a micro/macroburst? What is the difference between them?

Answer 16

A MICROburst is a very intense, narrow Downdraught that often forms from a storm formation (AC, CB, TCU).
They tend to be smaller than 4km, and last less than 5 mins

A MACROburst tends to be larger than 4km, and last longer than 5 mins

A dry downburst may not be visible on radar - but Virga is a sign.

Question 17

What are the dangers of Windshear?

Answer 17

Occurring as a result of a microburst - windshear comprises of very fast moving up/downdraughts.

1) Updraught (bouncing off the ground) forces A/C higher (energy gain)
2) Main downdraught forces A/C lower (energy loss)
3) Updraught (bouncing off ground) forces A/C higher (energy gain)

Question 18

What is lightning, and what are the dangers?

Answer 18

Electrostatic discharge, that develops down ionised channels (leaders)

A bolt travels at 140,000mph, with a temperature reaching 30,000°C
Which can lead to a supersonic shockwave through the heated air (Thunder)

If struck, can result in:
blindness, airframe damage, instrument error, loss of hearing

Question 19

Where does most hail form?

Answer 19

80% of hail forms within the upper Tropopause (45,000ft)

Question 20

What is the order of effectiveness of radar return on different types of precipitation?

Answer 20

1 - Wet hail
2 - Rain
3 - Hail
4 - Wet snow
5 - Dry hail
6 - Dry snow