Thunderstorms: The Science Bit

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By ITV Weather Presenter Becky Mantin

Many areas recorded their hottest temperature of the year so far with highs of 32C in Chelmsford.

However, early this morning thunderstorms bringing torrential downpours swept in from the continent and have continued to push northwards throughout the day.

But what actually is a thunderstorm and why do they occur?

Thunderstorms are more common than you might expect, with 40,000 a day around the world.
Thunderstorms are more common than you might expect, with 40,000 a day around the world. Credit: Reuters

Thunderstorms are basically enormous, electrically charged showers caused by intense heating of the ground, resulting in the air rising rapidly and then cooling and condensing to form raindrops.

The cloud rises to 10,000 metres (the height of Mount Everest!) with the top of the cloud well below freezing point and a flat head of ice crystals appears, shaped like a blacksmiths’ anvil.

Strong convective currents churn the raindrops in the cloud around, sweeping them upwards in the cloud over and over again to form hailstones.

Hailstones the size of a grapefruit and weighing as much as a kilogram have been recorded.
Hailstones the size of a grapefruit and weighing as much as a kilogram have been recorded. Credit: Reuters

Turbulence in the cloud causes friction between ice pellets and droplets, which in turn causes opposing electrical charges to build up.

The top of the cloud and the ground below become positively charged, but the cloud’s base is negatively charged.

These opposite charges are strongly attracted to each other, resulting in a huge rapid electrical discharge, a flash of lightning.
These opposite charges are strongly attracted to each other, resulting in a huge rapid electrical discharge, a flash of lightning. Credit: Reuters

In a fraction of a second the air is heated to over 20,000C, the air expands rapidly and we hear a clap of thunder.

When the hail is heavy enough it falls with torrential rain and runs the risk of localised flooding.
When the hail is heavy enough it falls with torrential rain and runs the risk of localised flooding. Credit: PA

Be prepared for more thunderstorms overnight tonight and throughout the day tomorrow.

Be warned there is Met Office Weather Warning out for midnight Friday night until midnight Saturday night for very heavy, potentially thundery rain giving dangerous driving conditions and the risk of localised flash flooding.

It’s going to be an uncomfortably warm and humid day and showers, potentially thundery, will continue throughout Sunday, mainly across eastern areas.

The weather looks to gradually settle down and improve for early next week.

Read more: Rude awakening as 3,000 lightning strikes move across the UK