Why are we getting thunder and lightning?

11 04 2012

With the weather in April being distinctly showery so far, what exactly causes this changeable weather and why do some showers give thunder and lightning?

 

Thunderstorms are normally associated with convective clouds which form from rising air warmed by the Sun. At this time of year we have longer days and therefore more heat reaches the Earth’s surface giving a greater chance for convective clouds to form. The air is continuously moving within the cloud in a very disorderly fashion, allowing the cloud to grow and water droplets or ice crystals to form. Given enough time and growth, the cloud may develop into a Cumulonimbus cloud and give quite heavy bursts of rain or hail for short periods of time, and possibly thunder and lightning.

Hail forms when ice crystals or frozen raindrops within the cloud get thrown about with the rapidly circulating air. As they ascend they grow as water freezes on the surface of the droplet or crystal. Eventually the droplets will become too heavy to be supported by the updraughts of air and they fall to Earth as hail.

 As hail moves through the cloud it picks up a negative charge as it rubs against smaller positively charged ice crystals. A negative charge collects at the bottom of the cloud where the heavy hail collects, while the lighter ice crystals remain near the top of the cloud and create a positive charge. The negative charge is attracted to the Earth’s surface and other clouds and objects and when the attraction becomes too strong, the positive and negative charges come together, or discharge, to balance the difference in a flash of lightning. The rapid expansion and heating of air caused by lightning produces the accompanying loud clap of thunder.

 Thunder and lightning facts:

  • A bolt of lightning lasts on average for about one 10,000th of a second.
  • The average speed at which the lightning cuts through the air is 270,000 mph.
  • There are several types of lightning, the most common being “sheet lightning” in which the discharge of positive and negative charges occurs within the cloud.
  • The risk of being struck by lightning is minimal and ninety percent of lightning travels from cloud to cloud. Lightning takes the shortest and quickest route to the ground, usually via a high object standing alone.
  • The average annual frequency of lightning is less than 5 days in western coastal areas of the United Kingdom and over most of central and northern Scotland, and 15 to 20 days over the east Midlands and parts of southeast England

Get more facts from our thunderstorms fact sheet.

See lightning observations for the last three hours on our observations map.


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3 responses

12 04 2012
Tony William Powell

Hi Dave,

I was one of the few who received Thunder on the 10th April, making my 2nd Thunder day of the year. A friend reported that they heard Thunder previously on the 3rd March. As this latter date was not my observation, are you aware of any sources on the web where this could be confirmed or otherwise?

Kind Regards

Tony Powell

17 04 2012
Dave Britton

Tony, it is entirely possible that there was thunder on the 3rd of March. However I am unable to confirm as I am not too sure of the location or observation time. If you would like to share observations or compare observations with others you can visit the Met Office Weather Observations Website, WOW, at http://wow.metoffice.gov.uk

17 04 2012
Tony William Powell

That is another great resource. As to the location, it was Newbury in Berkshire.
I will continue to look for other sources and get back to you if I find anything of interest to both of us.

Oddly another Thunder day as I type this.

Kind Regards

Tony Powell

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