19 August 2011
The red arrow is pointing at the overshooting top on the thunderstorm, indicating a very strong updraft. The BBC says 4 were killed when a stage collapsed at a music festival. Surface weather obs (from just before the storm developed) indicated temps near 27℃ (80℉) and dew-points near 18℃ (64℉). A surface front was moving into Belgium as a strong upper level trough pushed through the UK, and this set the stage for severe storms in a place that sees few of them.