Definition
CS is the standard meteorological abbreviation for cirrostratus, a high-altitude, thin, sheet-like ice-crystal cloud that often covers large portions of the sky and can produce a halo around the sun or moon. It appears in aviation weather products such as METARs, TAFs, area forecasts, and pilot reports to indicate the presence and layer of cirrostratus cloud.
Plain English
CS stands for cirrostratus -- a thin, high, milky-looking sheet of cloud made of ice crystals. It often covers the whole sky and can put a halo around the sun or moon. When you see CS in a weather report, the forecaster is telling you cirrostratus is up there.
Context Anchor
Seen in aviation weather reports, forecasts, and briefings that use cloud-type abbreviations.
Derivation
From Latin 'cirrus' meaning 'curl' or 'wisp' (high, wispy clouds) and 'stratus' meaning 'spread out' or 'layered.' Together, cirrostratus means a high, spread-out layer -- which is exactly what the cloud looks like.
Why Pilots Care
Helps assess overall weather picture and potential for changing conditions even though these clouds themselves rarely affect flight directly.
Grounding Statement
Picture a thin, white veil of cloud spread across most of the sky -- the sun still shines through, but with a faint ring around it. That's cirrostratus, and that's what CS means in a weather report.
Intuition Check
Do not read CS as a ceiling value or a report status. In this weather context, CS names a cloud type: cirrostratus.
Example Sentence 1
The area forecast showed CS moving in ahead of the front, so I expected the ceilings to drop within the day.
Example Sentence 2
Pilots noted the CS layer on the METAR and expected possible halo effects around the sun during the approach.