Cirrus spissatus
Ci spi
Cirrus spissatus
© Wetterkurs.ch
Description
The name "spissatus" (Latin: thickened, dense) describes a cirrus that is so compact and optically dense that it can partially or completely obscure the sun. In contrast to the delicate, translucent forms of other cirrus types, Cirrus spissatus appears as a grey-white to whitish field in the sky that looks noticeably thicker. These clouds frequently form from the upper parts of powerful cumulonimbus clouds (known as anvil remnants) or through strong lifting processes in the upper troposphere. They consist entirely of ice crystals and can reach a considerable horizontal extent. Cirrus spissatus is the densest of all cirrus types and sometimes forms the transition to cirrostratus.
Identification Features
- Dense, compact cirrus fields that are noticeably less translucent than other cirrus types
- Grey-white to whitish colouring; the sun is measurably dimmed or completely obscured
- Often lacking the typical fibrous or hair-like structure of other cirrus clouds
- May appear as a remnant of a cumulonimbus anvil
- Located at great altitude, typically above 6,000 metres
- Sometimes casts a visible shadow on lower cloud layers when the sun is low on the horizon
- Edges can trail off in a fibrous manner, while the centre remains opaque
- Distinguished from cirrostratus by a more limited, less uniform extent
Occurrence by genus
Highlighted: all genera with which spissatus occurs.
Meteorological Significance
Cirrus spissatus can carry different meteorological significance depending on its origin. If it derives from the remnants of a cumulonimbus anvil, it indicates past thunderstorm activity and has no immediate forecasting relevance. However, if it appears ahead of an approaching warm front, it can be regarded as a harbinger of increasing cloud cover and subsequent precipitation. In conjunction with a build-up and spread of high clouds, Cirrus spissatus can indicate a deterioration in weather within the next 12 to 24 hours. When occurring in isolation, it is generally of little meteorological significance.
Facts
- WMO-Code
- Ci spi
- Height layer
- High clouds
- Typical height
- 6.0 - 12.0 km
- Genus
- CIRRUS