MET - Thunderstorms

What is a thunderstorm defined as?

• thunder and lightning manifested by clouds at least 10,000ft high

• CB cloud with an anvil and showers of hail for more than 10mins

• at least 4 electrical discharges from a cloud with at least 20,000ft for vertical extent

• one or more electrical discharges shown with thunder and lightning

Requirements for a thunderstorm?

Select all that apply

• unstable air through a deep layer

• adequate supply of moisture

• wind of at least 15kts

• 'trigger' action

• mechanism to provide electrical charge

How is lightning formed?

• from the solar radiation heating the top of the CB cloud creating static electricity

• from ice particles colliding into other ice particles

• from water molecules splitting into their component hydrogen and oxygen atoms, releasing static electricity

• from the electrostatic interference of varying layers of stratus cloud

What causes thunder?

• The expansion of air as a spark passes through

• Two or more ice particles colliding at great speed

• Updraughts and downdraughts colliding near the centre of the cloud

• Air particles expanding and exploding due to the high instability of air

Which stage of development would 'all draughts be upward'?

• growing

• mature

• decaying

Why may no precipitation fall from a CB during the growing stage of a thunderstorm?

• dew point of the cloud is too low

• updraughts may be too strong

• cloud water content is not great enough

• downdraughts may be too strong

Which statement is correct regarding the mature stage of a thunderstorm?

• the updraughts are stronger than the downdraughts

• the downdraughts are stronger than the updraughts

• lightning and thunder activity have ceased by this stage

• the updraughts and downdraughts interact to cause moderate turbulence

Squall line is also known as....

• thundercloud

• gust front

• small quail

• freezing level

How long does the growing stage of a thunderstorm last?

• 5min

• 20min

• 60min

• 2hr-3hr

What causes a gust front?

• The downdraughts striking the surface during the mature stage

• The updraughts causing the cloud to grow in size during the growing stage

• A thermal low forced to flow parallel to the coastline

• A cold front meeting warm air