I am watching the development for the possibility of thunderstorms during Thursday afternoon and evening. There will be a lot of instability and this will help cloud tops to reach over than 30,000 feet. This then gives us a risk of some big thunderstorms developing. Explanation of the echo sounding graph shows cloud base and height, So the dotted line starts around 1,000 feet (base of the cloud) and then re joins the red line after 30, 000 feet (top of the cloud). At the top of the chart you can see 874 Cap. All these indications give you the idea there is a risk of big thunderstorms developing.