The Airmass RGB image from Meteosat-10 shows a cold pool crossing the UK and Ireland on 22 March.
The convective cloud associated with this cold pool caused heavy showers, with thunder, hail and snow.
In the imagery there is a change in colour, from a purple in the centre of the cold pool, marking the coldest air, to a reddish brown colour, closer to the cold side of tightest gradient of thickness lines. There is then a distinct change to a blue/green colour — the warmer air surrounding the cold pool.
This change in colour is close to the 5280 m thickness line (shown as a blue dashed line). A thickness line is the vertical distance in meters between two pressure levels.
Although it is only a rough guide, the 5280 m thickness line is often referred to as the snow line. Areas of precipitation where the thickness is below this value are likely to fall as snow rather than rain. Across the UK heavy showers were reported with a mixture of rain, sleet and snow, some with hail and thunder.