Altocumulus translucidus
Ac tr
Altocumulus translucidus
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Description
Translucidus (lat. translucent) denotes a variety of altocumulus in which the cloud patches or layers are sufficiently translucent to reveal the position of the sun or moon. The cloud elements appear as regular patches, plates, or rolls at mid-level altitude and allow light to pass through diffusely. Altocumulus translucidus is one of the most common forms of altocumulus and often occurs in extensive fields that can cover large portions of the sky. Despite its sometimes widespread extent, the cloud layer remains thin enough that the outlines of the sun or moon remain faintly visible. This variety is particularly striking at low sun angles, when the translucent light highlights the cloud elements in colour.
Identification Features
- Cloud field composed of individual patches, plates, or rolls at mid-level altitude
- The sun or moon is discernibly visible through the cloud layer
- Cloud elements do not cast complete shadow on the ground
- Apparent size of individual elements is between 1° and 5° (approximately one to three finger widths at arm's length)
- Regular, often mosaic-like arrangement of cloud elements
- The layer is thin enough that shading and brightness variations remain visible across the sky
- Distinction from Altocumulus opacus: with translucidus, the position of the sun or moon is always discernible
Occurrence by genus
Highlighted: all genera with which translucidus occurs.
Meteorological Significance
Altocumulus translucidus is in many cases a fair-weather cloud and indicates stable conditions in the middle troposphere. However, if this cloud becomes progressively thicker or consolidates into Altocumulus opacus, it may signal an approaching disturbance or frontal passage. Altocumulus translucidus appearing in the morning can be a precursor to convective development in the afternoon, particularly during the summer months. In combination with a lowering cloud base and increasing cloud cover, deteriorating weather and possible precipitation within 12 to 24 hours should be anticipated.
Facts
- WMO-Code
- Ac tr
- Height layer
- Mid-level clouds
- Typical height
- 2.0 - 6.0 km
- Genus
- ALTOCUMULUS