The autumn sky over the Mendip Hills of Somerset, England looked tortured as roiling clouds stretched and arched their way across the landscape. Helen Crawley (Member 50,003) had spotted an expanse of Stratocumulus lacunosus asperitas and remarked that ‘It was one of the most unusual skies I have ever seen.’

The holelike details in the layer of cloud are the lacunosus elements, caused by sinking parcels of denser, cooler air. The dramatic wavelike undulations are the asperitas elements, sculpted by turbulent winds. When such buckled formations appear together, there’s usually a storm cloud at work in the vicinity. Sure enough, Helen’s clouds were accompanied by a Cumulonimbus. Though the towering height of the storm cloud was hidden from view, you can see its showers darkening the horizon to the left, where Helen recalls it was producing heavy rain and dramatic flashes of lightning.