After one of the driest and warmest Aprils on record we're finally seeing the month live up to its name with plenty of showers today, but why the change?

Well for the last few weeks the jet stream has been to the north of the UK. On the northern side of the jest stream is cold air and to it's south is warm air, that's what drives it. So we've been basking in warm air and settled weather.

However, at the moment the jet stream is running towards northwest France and Spain, bringing colder air and more changeable weather to the West Country.

Jet stream position this April

So what is it about showers in particular when it comes to April? Well it's because the air tends to be very unstable. Warm air wants to rise, and at this time of year the sun is strengthening, the earth heats up more and creates warm air at the surface. However, if colder air is sitting above, as we have at the moment, it creates a lid trapping the warm air below.

It wants to shoot upwards and break through the layer of colder air, rising and cooling rapidly as it does so, creating huge clouds that produce heavy showers. If the air is really unstable it can lead to thunderstorms too, producing cumulonimbus clouds with tops that can reach well above 25,000 feet!

Cumulus clouds producing showers above Odd Down, Bath. Credit: Ruth Wishart
Heavy showers across Dartmoor. Credit: Rod Stevenson
Contrasting skies as a shower cloud moves overhead. Credit: ITV West Country

Spring is therefore quite a topsy turvy season when it comes to weather as we make the transition from the end of winter to the start of summer. The atmosphere is taking on all that extra heat and moisture and we tend to see it in the form of downpours one minute, and sunshine the next.