Atmospheric optics expert Les Cowley explains the special conditions required to create such a cloud: "Take an unusually cold lower stratosphere (15-25km high), use some gravity waves generated by high winds and storms in the troposphere to stir in some water vapour, and -- voilà! You get these clouds made of tiny ice crystals shining after sunset with unforgettably bright iridescent colors."
"The very special conditions make nacreous clouds a rare, high-latitude phenomenon. Scandinavia, Iceland and northern Canada are favourite places to see them. Sightings in the southern hemisphere are even more rare because there is so little land far enough south except for Antarctica." www.spaceweather.com