Stratocumulus

How to recognise it

• Large rounded masses or rolls, often organised into rows or a honeycomb pattern.
• Each element is wider than three fingers held at arm's length — noticeably bigger than altocumulus.
• A mix of grey and white in the same layer, with distinctly darker undersides.
• Gaps of blue or brighter sky between the elements, unless the layer closes over completely.

What weather it signals

• Generally benign. Stratocumulus produces at most light drizzle or a few flakes of snow.
• It often forms when a cumulus layer spreads out and flattens against a temperature inversion in the late afternoon or evening.
• A stratocumulus deck breaking up during the day usually means clearing skies ahead.

How to photograph it

• Sunset is the best moment. Low light picks out the three-dimensional structure of the rolls and the gaps glow.
• Use a wide angle to show the repeating pattern across the whole sky, which is what makes the cloud recognisable.
• Shoot toward the brighter gaps for contrast rather than at the flat grey centre of the deck.

Fun facts

• Stratocumulus covers a greater fraction of the Earth's surface than any other cloud genus, dominating the cool subtropical oceans.
• Because it is bright and low, it reflects a large amount of sunlight back to space and is one of the most important — and most uncertain — factors in climate models.
• It frequently forms in the evening as daytime cumulus loses its heat source and spreads sideways instead of rising.

Easily confused with

Frequently asked questions