The accessory cloud known as velum – Latin for the ‘sail’ of a ship – is often upstaged by the huge and dramatic formations that cause it to appear. Clouds like the blustery Cumulonimbus storm cloud in Palace of the Popes, Avignon by English artist Sir Claude Francis Barry. The velum clouds are the flat, extended horizontal strips flanking the towering storm cloud. Velum develop as the powerful vertical air currents rushing up within mighty convection clouds like these lift the more stable surrounding air, cooling it and encouraging its moisture to condense into sheets of droplets that hang in the air for some time. Understated accessory clouds like velum can’t compete for attention with the Cumulonimbus storm clouds that create them. Instead, they linger meekly in the shadows of such huge Gothic piles of the sky.