Cirrus Uncinus Clouds: Australian Mare's Tails Explained

Cirrus uncinus clouds, also called mare's tails clouds, are high-level clouds made of ice crystals. Their hooked shape usually appears when wind shear bends falling ice crystals into a curved tail. In Australia, they often sit ahead of changes in the weather and can help with weather forecasting.

Key takeaways

• Cirrus uncinus are high-level clouds made of ice crystals.
• Their hook shape forms when wind shear stretches the falling ice crystals.
• They are a useful clue for weather forecasting, especially when fronts are nearby.
• The Bureau of Meteorology (BOM) notes that cirrus uncinus can show wind shear in the atmosphere.
• They do not usually bring rain themselves, but they may appear before thicker cloud bands.

How Wind Shear Forms Cirrus Uncinus

Cirrus uncinus forms high in the atmosphere, where the air is cold enough for water vapour to become ice crystals. As those crystals fall, wind shear changes their path. Stronger winds higher or lower down can stretch the cloud into a hooked tip, which is why these clouds are also called hooked cirrus clouds.

The Bureau of Meteorology has used cirrus uncinus as an example of wind shear in the upper atmosphere. That makes them useful for weather forecasting because they can hint at changing airflow well before rain reaches the ground.

What causes mare's tails clouds?

Mare's tails clouds form when ice crystals fall into air layers that move at different speeds. The ice trails are pulled sideways and thin out, leaving long, feather-like streaks with a curved hook at the end.

What Cirrus Uncinus Means for Australian Weather

In Australia, cirrus uncinus clouds often appear ahead of fronts, especially when a change in the jet stream is helping to steer new weather systems across the country. They can be an early sign that high cloud is spreading in advance of thicker cloud bands. For local cloud spotting, see Weather Charts & Maps and How Forecasts Work.

What do cirrus uncinus clouds signify for weather in Australia?

They usually point to upper-level moisture, wind shear, and changing weather. They are not rain clouds themselves, but they can appear before a front or a broader cloud shield arrives. In that way, they are one of the weather forecasting clouds that can help show what may happen next.

What do cirrus uncinus clouds mean?

They often mean the upper atmosphere is becoming more active. If you also see altostratus or thicker cloud spreading in behind them, the chance of rain can increase as the system moves closer.

Are cirrus uncinus clouds a sign of rain?

Not on their own. They are ice crystal clouds, so they sit high above the rain area. But if they are followed by altostratus, nimbostratus, or a thickening cloud band, rain may be on the way.

Cirrus Uncinus vs. Other Cirrus Cloud Types

Cirrus uncinus is one type within the broader cirrus family. The main difference is the hook or comma shape at the end of the streak. Other cirrus clouds can look wispy, fibrous, or dense without that obvious curled tail.

Cirrus Uncinus vs. Other Cirrus Cloud Types

Standard cirrus clouds are thin, white, and fibrous. Cirrus uncinus has the same icy origin, but the hooked tail sets it apart. Cirrus spissatus is a denser form of cirrus that appears greyish in patches, while cirrus uncinus is a comma-shaped cirrus cloud terminating in a hook; cirrocumulus uncinus is not given as a standard International Cloud Atlas species name.

What is the difference between cirrus and cirrus uncinus?

Cirrus is the wider cloud type. Cirrus uncinus is a specific form of cirrus with a hook at the end, made by wind shear acting on falling ice crystals.

Cloud formations Australia sky watchers often notice

Across Australia, cloud formations can change quickly as fronts move through southern states, and as tropical systems send upper-level cloud outward. If you watch the sky regularly, it helps to compare cirrus with lower cloud layers and note whether the cloud is building, thinning, or spreading. For more on local weather pages, see Sydney Weather, Melbourne Weather, and Brisbane Weather.

Large storm systems can also send ice cloud outflow far from the core. For example, tropical cyclones can spread upper-level cloud well away from the main storm. To read more about that side of weather, see Worst QLD Cyclones and Tropical cyclone formation Coral Sea.

Cirrus clouds are one part of the bigger picture. For a broader guide to cloud types, see Clouds explained.