Field Guide / Clouds & Weather Signs
Cirrostratus
halo cloud
A thin, milky veil that covers much of the sky and often makes a ring, or halo, around the sun or moon. It is a common early sign of rain or snow.
- Height
- High Clouds
- Abbreviation
- Cs
- Typical altitude
- Above about 20,000 ft (6,000 m); made of ice crystals
- Usually means
- Rain or snow likely
How to recognize it
- A thin, transparent, whitish sheet covering all or part of the sky.
- The sun or moon shows through with a clear outline.
- A ring, or halo, around the sun or moon is a classic sign. It is caused by ice crystals bending the light.
What it usually means
- A halo around the sun or moon often comes before rain or snow, commonly within about a day, as the veil thickens and lowers.
- If the veil thickens to a gray sheet and the halo disappears, it has probably turned into altostratus and rain is closer.
- The old rhyme, a ring around the moon means rain soon, is a rough guide rather than a forecast.
What to do outdoors
- Plan for a change: pack rain layers and think about where you will shelter.
- If you are heading for exposed ground, aim to finish before the weather arrives.
- Check the National Weather Service forecast for a front.
Often confused with
- Cirrus: separate wispy streaks, with no continuous veil.
- Altostratus: thicker and gray, with a dim sun and no halo.
Field notes
A halo is one of the easiest weather signs to see. Cirrostratus usually forms ahead of a warm front, so the weather often turns within a day.
If you can see the sun with a clear outline and a ring around it, you are looking at cirrostratus.
Related guides
Cloud signs are rough guides, not forecasts. Always check the National Weather Service forecast at weather.gov before and during a trip, carry a way to receive alerts, and treat any watch or warning as a reason to change your plans. If you can hear thunder, you are close enough to be struck by lightning.