GlossaryMamma (mammatus)
Supplementary feature · Special
Mamma (mammatus)
mamma
Definition
A supplementary cloud feature consisting of hanging, pouch-like protuberances on the underside of a cloud, most often a cumulonimbus anvil or the underside of an altocumulus or stratocumulus layer.
Field note
The pouches are saturated descending parcels that cool as they sink, which is why they keep a sharp shape while the rest of the cloud dissolves. They are seen most often near sunset, when a low sun angle rakes across them.
- Added
- 1 August 2026
- By
- Class
- Supplementary feature
- Band
- Special
Read the full field note
Mammatus: the pouches that mean the storm is leaving
Mammatus is one of the few cloud features that is unmistakable once you have seen it: a ceiling of smooth, hanging pouches, usually on the underside of a cumulonimbus anvil. It is spectacular, it is frequently described as a sign of a severe storm, and the folklore around it is mostly wrong in an interesting way.