Clouds Formation Before The Storm

The polar air in the mesosphere is, counter-intuitively, colder during the summer so it is mostly at this time of year that noctilucent clouds are seen. They can occasionally be seen illuminated by the sun during deep twilight at ground level. Noctilucent clouds are the highest in the atmosphere and occur mostly at altitudes of 80 to 85 kilometers (50 to 53 mi), in the mesosphere. An alpha-numeric sub-classification is used to identify variations in physical appearance.
- Type 1: Very tenuous noctilucent resembling cirrus fibratus.
- Type 2: Bands; noctilucent in the form of long streaks, often in groups or interwoven at small angles similar to cirrus intortus.