Cloud enthusiasts in northwest England have been treated to the unusual sight of a Helm Bar.
This special type of lenticular cloud is caused by the Helm Wind, a strong north-easterly which blows down the south-west slope of the Cross Fell escarpment.
Although many other mountain regions in Britain exhibit the same phenomenon when the weather conditions are favourable, the Helm Wind is unique to Cumbria and is the only named wind we have in the British Isles.
This wind can cause a low rolling wave cloud, called a Helm Bar - the formation of a dense cap of cloud - but is also referred to as Helm Bar Cloud, Wave Cloud, Altocumulus Lenticularis, Elongated Lenticular Cloud, Voltus and Roll Cloud.
Lenticular cloud itself isn't unique - we often get altocumulus lenticularis or wave cloud to the lee of high ground - it's the named wind that's specific to Cumbria.