What Type Of Cloud Is This/how Are They Formed?

[Things]

Some stormy and rainy weather around here, and I found these in the sky. I havent seen these in person before, so how are they formed and what are they called?

Cheers,

Dan :o

[J07]

Looks like Mammatus...

[stormchaser1]

Looks like Mammatus to me as well

if they are Mammatus these are formed when a localized downdraught carries cold air down into a warmer layer, causing it

to cool to its dewpoint and produce cloud droplets. This process has been termed `upside down convection` drawing a parallel with the commonly seen process where a thermal carries warm air upwards and gives no cloud

The Mamma seen beneath many types of cloud are relately small and not praticularly pronounced, but beneath cumulonimbus clouds they may assume various forms and are sometimes extremely striking,.

nigel