Mysterious Clouds: How and why did they form?

It's been a wild weekend for many of us with some crazy weather sweeping through the East and West Midlands.

And it wasn't just heavy rain, thunder and lightning that lit up the skies there were some weird and wonderful cloud formations that many of you caught on camera.

So what happened?

An area of low pressure slowly drifted up the western side of Britain pushing a cold front our way. Ahead of the cold front, we saw some very high temperatures and when the cold front then pushed north on Sunday it introduced cooler conditions to end the weekend. In fact temperatures dropped a good 10 degrees. This big temperature contrast across this cold front helped to make it a really active feature and gave us the thundery downpours.

We saw 10-12mm in the hour in a few places across the West Midlands on this front, and about 15-20mm in total as it passed. Amounts across the East Midlands were much smaller.

Now sometimes on the leading edge of an active cold front or thunderstorm you find these huge clouds known as Shelf Clouds. Within the front there is lots of unstable air rising and falling. So it was these strong downdraughts that essentially ‘scooped’ up the warm air ahead of them, and formed shelf clouds you see. They are horizontal and wedge shaped and attached to the base of the thunderstorm.

What it also produced is a roll cloud which is quite rare and unlike the shelf cloud is detached from the thunderstorm or cumulonimbus base and appears to be slowly rolling.

Both roll clouds and shelf clouds are collectively Arcus clouds (from the latin for “arch”) and get their names purely from their looks.

As we saw this weekend both clouds produce a wonderful display in the sky, not necessarily what you would expect in late August.