Soaking thunderstorms expected on Saturday

As we’re halfway through the week, I thought I’d look ahead to the start of the weekend, with some lively weather on the cards for Saturday.

Now that June has arrived, from a meteorological perspective, we are now in summer, with the longest day of the year just over two weeks away.

With the sun approaching its highest point in the sky in the northern hemisphere, the amount of heat energy being injected into the atmosphere is heating up the continents markedly. 

As is the case for any system that contains energy, the greater the amount that is present, the greater the potential for something to happen, if and when it is released.

In meteorology, a situation where the atmosphere contains a lot of potential energy is often referred to as a loaded gun scenario. In a nutshell, this means that if the right conditions exist to cause the trigger to be released, then things can get very lively.

Ingredients for a thunderstorm

Weather is driven by contrasts in temperature, pressure and humidity (moisture levels), with the most active weather taking place when these contrasts are most extreme.

When it comes to thunderstorm formation, it is down to the collision of cooler air with warm, moist air. As the two collide, the warm, moist air is thrown way up into the atmosphere to around 30,000ft – the height at which commercial airliners fly.

It is effectively like taking the lid of a saucepan of cooking popcorn, resulting in the bubbles of air rushing rapidly upwards in the atmosphere, forming cumulonimbus clouds that produce thunder, lightning, heavy rain, hail and gusty winds.

Later this week, such conditions will be in place across the UK, with the potential for some lively weather to start the weekend.

On Friday, a slow-moving area of low pressure will sit a few hundred miles to the south west of the UK. This will pump up warm, humid air from France and Spain, where temperatures will be around 24-32C.

Part two of the thunderous cocktail will come on Saturday, as cooler air moves in off the Atlantic and colliding with the warm, humid air lying in waiting.

What to expect on Saturday

The first point to emphasise is that there is still significant uncertainty in the timing of and position of the most active thunderstorms on Saturday.

Nevertheless, most of the weather computer models suggest that through the day, a band of rain with embedded thunderstorms will sweep north eastwards across the UK. This will deliver heavy downpours, with hail, thunder, lightning and gusty winds.

Given that some of the rain could be very intense, there is a risk of some flash flooding – something highlighted on the Met Office’s weather warning page today.

You may have seen rather more dramatic articles in the Daily Express and Daily Star today regarding Saturday’s weather, but this is my take on what is going to happen, paralleled by other credible sources such as MeteoGroup and the Met Office.

Don’t forget, you can get the latest forecast on the Channel 4 Weather website. I’ll also be posting regular updates on Twitter – @liamdutton