14 Thunder Storms

Question 1

Conditions required for a thunderstorm

Answer 1

1. Unstable air
2. Humidity
3. Trigger

Question 2

Triggers for a thunder storm

Answer 2

• Orthographic
• Frontal
• Thermal / Convection
• Low Pressure / Convergence

Question 3

Types of Thunderstorm

Answer 3

1. Frontal - warm air is forced up and over a cold front
2. Air Mass - Cold air moves in over a warm surface. Air is heated from below via conduction which then rises
3. Heat/Thermal - Surface reaches its hottest point in the afternoon so ELR > DALR as air is heated from the surface.
4. Squall Line - Line of thunderstorms along a cold front. Multi-cell storm. Most severe conditions.

Question 4

Name the phases of a Thunderstorm

Answer 4

1. Initial / Cumulus / Building
2. Mature
3. Dissipating

Question 5

Key facts on Cumulus stage of a thunderstorm

Answer 5

• Up drafts build the cloud up
• Up drafts can reach speeds of 60kts
• Area of low pressure can developers underneath due to up drafts
• Lasts 15 to 20mins

Question 6

Key facts about the mature stage of a thunderstorm

Answer 6

• Strong up drafts and down drafts
• Latent heat absorbed (Evaporation) - stronger downdrafts
• Rain and Hail
• Updrafts up to 100kts
• Static charge developed by friction between perspiration
• Positive at top, negative at bottom
• Lightning - between -10 and +10 degrees C
• Front gusts 15-20 miles in front - Roll cloud
• Microbursts, area <5km, <5mins
• Macrobursts, area >5km, >5mins
• Lasts 15 to 20 mins
• Max height - 60 to 70K Ft
• 6000ft from surface

Question 7

Key facts about Dissipating stage of a thunderstorm

Answer 7

• Downdrafts overcome updrafts
• Sinking air evaporates - cloud disperses
• Lasts 1.5 to 2.5 hours

Question 8

Speed of thunderstorm:

Answer 8

15 - 20kts

• Frontal storms travel the speed of the front
• These are the fastest storms

Question 9

Where in a storm are tornadoes found?

Answer 9

Trailing edge of a super cell

Question 10

Diameter of a tornado

Answer 10

100 to 150m

Question 11

Ground speed of a tornado

Answer 11

20 - 40kts

Question 12

Wind speeds in a tornado

Answer 12

200kts

Question 13

How long do tornados last?

Answer 13

Up to 30mins

Question 14

Where on the globe are tornados mostly found?

Answer 14

Mid-west USA

Late spring to early summer

Question 15

How are tornados measured?

Answer 15

On the Fujita scale

Question 16

Hazards associated with a thunderstorm

Answer 16

• Hail - up to 45k ft, structural damage, engine ingestion
• Static electricity - instrument damage, St Elmo’s fire
• Wind sheer - Most dangerous close to ground
• Turbulence
• Icing - Super cool water droplets
• Water ingestion - Engine flame-out, Keep engine igniters one
• Instrument error - Pressure readings, Air speed, Compass
• Virga

Question 17

Thunderstorm avoidance guidence

Answer 17

• Above 20,000ft, 20 miles

- Below 20,000ft, 10 miles

Question 18

What signals the start of the mature stage of a thunderstorm?

Answer 18

Start of precipitation

Question 19

Between the external appearance of a severe thunderstorm and the turbulence and hail that are contained within it, there is:

Answer 19

No Correlation

Question 20

What sort of cloud will often proceed Thunderstorms?

Answer 20

Castellanus