SIR, — This photo was taken outside my flat on Holywell Hill around 7.30pm on Tuesday after a brief downpour. I just grabbed my mobile and started snapping — just couldn t believe what I was looking at. It s definitely not your average St Albans twilight!

SIR, - This photo was taken outside my flat on Holywell Hill around 7.30pm on Tuesday after a brief downpour. I just grabbed my mobile and started snapping - just couldn't believe what I was looking at.

It's definitely not your average St Albans twilight!

IAN PATTISON,

Holywell Hill, St Albans.

n The Herts Advertiser forwarded the picture to the Met Office for an expert opinion on what weather conditions could create such a sight and why.

The explanation was that it was a good example of a cloud formation called mammatus which was usually associated with severe weather conditions.

A spokesperson for the Met Office explained that as the photograph shows, it is a spectacular and distinctive cloud formulation that consists of pendulous globules of cloud - mamma is the Latin for breast - that hang from the underside of stratocumulus or cumulonimbus clouds, especially underneath the anvil of the latter.

They are caused by powerful downdrafts when pockets of cold, moist air sink rapidly from the upper to the lower parts of the cloud, reversing the usual cloud-forming pattern of the upward convection of warm, humid air.

However if any readers have any views on the unusual cloud formation then please contact us on hertsad@hcn.co.uk or visit our website on www.hertsad24.co.uk