|Weather Reference - Thunder and Lightning
Cloud to Ground | Cloud to Cloud | Cloud to Air | Disclaimer
Thunderstorms occur under varied conditions but are most likely to occur in spring or summer in tropical and subtropical zones and also tend to occur in late afternoon or early evening when heat off the ground has reached its peak.
Each day approximately 40,000 thunderstorms occur worldwide and each may last up to two hours, although they will only be in their mature stage for only 15 – 30 minutes. After this they tend to dissipate. You can normally see if a storm is in the area if the terrain is flat and the sky is not obscured by low level stratus. A towering cumulonimbus cloud may be visible up to 200 miles away.
The best way to see which way the storm is heading is by observing the shape of the anvil of the cloud, as normally there are long and short parts to it with the long section spreading out in the direction in which the upper level winds are blowing.
You should be able to hear a thunderstorm up to twenty miles away, and because light and sound travel at different speeds you can approximate the storms distance by counting the intervals between a flash of lightning and the sound of the thunder. As a general guide, every five seconds interval is equivalent to one mile between you and the storm.
Cloud to Ground Lightning
lightning occurs when there is an electrical discharge within, or around a thunderstorm.
Cloud to ground lightning occurs when the electrical charge travels between a negatively charged cloud base and the positively charged ground.
This form of lightning is spectacular, forming brilliant jagged bolts between the sky and the ground which last a fraction of a second.
Most cloud to ground lightning occurs from the base of a cloud, however rarer forms known as positive flash occurs when positive charges higher up in a cloud react with negative ones on the ground, sending a huge lightning bolt from the top of the cloud to the ground.
The colour of the strike indicates the content of the surrounding air. The flash will appear red if there is rain in the cloud and blue if there is hail. Dust in the atmosphere will produce yellow lightning. White lightning indicates low humidity.
Approximately 20% of lightning hits the ground. To minimize your chances of being hit you should move indoors if possible, as lightning runs along electrics and plumbing in your home you are best avoiding using these items and even switching them off. If you are outside you should not shelter under a tree. Keep clear of metal objects. If you hair stands on end it may mean that you are within an area of positive charge below the cloud and that a strike is imminent. You should crouch down on all fours and keep your head low.
The greatest myth is that lightning never strikes the same place twice – the top of the Empire State Building in America is struck approximately 500 times per year!
Cloud to Cloud Lightning
This is the most common form of lightning and most often occurs within a cloud and involves electricity passing between negatively charged base of the cloud and it's positively charged upper level.
A large flash can produce a spectacular snapshot of an entire cumulonimbus which can remain visible for up to half a second if there is a succession of strokes up and down the leader path.
Cloud to cloud lightning can occur between two adjacent clouds if the electrical discharge is opposite, although this is less common.
Because cloud to cloud lightning happens at high altitudes it can be seen some distance away, especially at night.
Cloud to cloud lightning often appears to be a ‘silent storm' with frequent flashes illuminating the sky amid eerily silent surroundings.
Cloud to Air Lightning
This occurs when an electrical discharge takes place between a build up of one type of charge within a cumulonimbus cloud and an area of opposite charge in the surrounding atmosphere.
This tends to not be as powerful as cloud to ground lightning and one stroke is normally enough to reduce the differences in charges below critical levels.
It normally occurs between the air and the positively charged upper regions of the clouds.
It does not occur in the lower parts of the clouds but usually in combination with the positive flash form of cloud to ground lightning, when the cloud to air bolts will appear as weaker off shoots from the main flash and happens because in the lower layers of difference in charges between the cloud and the ground in normally greater than the difference in charges between the cloud and the surrounding air.
When cloud to air, or cloud to cloud lightning is obscured by clouds only a flicker reflection can be seen in the adjacent clouds, this is known as ‘sheet' lightning which is only an optical effect and is not true lightning.
All information is presented in good faith. We cannot accept any liability for any incorrect or incomplete information. You are strongly advised to seek clarification on any information presented. If you find any errors or omissions, please contact us to let us know so that we can put it right.