A convection rainfall day 5 August 2012
The chart shows a large area of low pressure across the UK.
Air in such a situation is said to be unstable. The sun heats the ground causing convection of the air above. As the air rises, clouds form, which ultimately give rain showers.
The phrase sunshine and showers is often used to convey the 'hit and miss' nature of the showers. One location may be experiencing a dry and bright day whereas a short distance away there may be heavy showers with hail and thunder. A look at the present weather over the course of the day will show that at any one time some places are dry and sunny, some have showers and some have thunderstorms.
In summer, during convective situations, the hotter temperatures are found away from the coast.
The coastal strip may stay dry and bright with inland areas seeing heavy showers.