Originally posted by HoutHans Wow, in Dutch these are called parelmoerwolken, mother of pearl clouds, but a very nice capture of some special clouds. Thanks for sharing.
Same as in Norwegian, then; perlemorskyer
I got some more information about the conditions required for them to appear in my area. It can happen when there's fairly moist air in the mountains to our west combined with gale force winds from the west pushing the moist air into the stratosphere (at 10-50 km altitude) causing clouds of ice particles to form (-15 to -50°C). The wavy form comes from the wind being "shaped" by the mountains, sort of a blueprint of the mountains. In addition the weather must be clear at lower altitudes and the time of day must be right (with the sun between 1° and 6° below the horizon).