Stratus undulatus
St un
Stratus undulatus
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Description
The name "undulatus" (Latin: wave-shaped) describes the characteristic wave structure of this stratus variety. Stratus undulatus appears as a low, uniform cloud layer traversed by clearly visible waves or undulations. This wave-like structure is formed by wind shear at the upper or lower boundary of the cloud layer, where air layers of different speeds or directions meet. The cloud appears as a grey layer, often covering the entire sky, with parallel light and dark stripes or bands. Compared to other stratus varieties, the wave structure is the most prominent distinguishing feature.
Identification Features
- Low, extensive cloud layer with a clearly visible wave pattern
- Parallel light and dark stripes or bands within the cloud deck
- Uniform, grey base layer typical of stratus, but with a wave-like modulation
- The wave crests may appear as slightly thickened, darker areas
- Cloud base is typically very low, often below 600 metres
- Wavelength of the undulations ranges from a few hundred metres to several kilometres
- When viewed from the ground, it can resemble a rippled ceiling or corrugated surface
- Can be distinguished from Stratocumulus undulatus by the absence of clearly separated cloud elements
Occurrence by genus
Highlighted: all genera with which undulatus occurs.
Meteorological Significance
Stratus undulatus indicates pronounced wind shear in the lower atmospheric layers, where air masses of different speeds or directions meet. The wave structure can be a sign of slight dynamic instability within an otherwise stable stratification. This cloud form frequently occurs during calm, moist weather conditions, with drizzle being possible. A dissipation of the wave structure may indicate increasing mixing and a possible break-up of the cloud layer. However, if the layer persists, continued overcast and damp weather is to be expected.
Facts
- WMO-Code
- St un
- Height layer
- Low clouds
- Genus
- STRATUS