What Is Low Cloud Cover?
Low cloud cover refers to clouds that form in the lowest part of the atmosphere, relatively close to the Earth’s surface. These clouds can cover part or all of the sky and often create dull, grey conditions.
Common low clouds include stratus and stratocumulus clouds. Depending on their thickness and moisture content, low clouds may produce light rain, drizzle, mist or light snow.
Low cloud cover can also affect visibility, particularly when the cloud base becomes very low. In some situations, clouds can reach the surface and effectively become fog.
Related Conditions
| Condition | Description |
|---|---|
| Overcast | A sky condition in which clouds cover nearly all or all of the visible sky. |
| Low Ceiling | A condition in which the base of the lowest significant cloud layer is unusually close to the ground. |
| Stratus Clouds | Low, widespread clouds that often create a uniform grey layer across the sky. |
| Stratocumulus Clouds | Low, lumpy cloud layers that can cover large portions of the sky while allowing occasional breaks. |
| Broken Clouds | A sky condition where clouds cover most, but not all, of the sky. |
Related Alerts
| Alert | Description |
|---|---|
| Fog Advisory | Issued when widespread fog is expected to significantly reduce visibility. |
| Freezing Drizzle Advisory | Issued when freezing drizzle is expected to create icy and hazardous surfaces. |
| Rainfall Warning | Warns when significant rainfall is expected to create hazardous conditions. |
| Snowfall Warning | Warns when significant snowfall is expected to reach warning criteria. |
| Winter Storm Warning | Warns of a significant combination of hazardous winter weather conditions. |
What Causes Low Cloud Cover?
Low cloud cover develops when moist air near the Earth’s surface cools enough for water vapour to condense into tiny water droplets or ice crystals.
This can happen in several ways. Moist air may cool overnight, move over a colder surface or be lifted slightly as it travels across changing terrain. Weather systems can also bring widespread moisture into the lower atmosphere and create extensive layers of low cloud.
Stable atmospheric conditions are particularly favourable for widespread low clouds. Instead of rising high enough to form tall clouds, moist air remains trapped relatively close to the surface and can spread horizontally across a large area.
Stratus clouds are a common result and can create overcast skies that persist for hours or even days.
When the base of a low cloud layer reaches the ground, the suspended water droplets are considered fog. This is why low clouds and fog can sometimes appear very similar, especially around hills, elevated terrain and other areas where the ground intersects the cloud layer.
FAQ
Low clouds generally have bases within roughly the lowest 2 kilometres of the atmosphere, although their exact height varies with weather conditions and location.
Stratus and stratocumulus are two of the most common types. Both can spread across large portions of the sky at relatively low altitudes.
No. Low cloud cover describes the altitude of the clouds, while overcast describes how much of the sky is covered. Low clouds can create overcast skies, but they can also cover only part of the sky.
They are closely related, but not exactly the same. Fog is essentially a cloud at ground level. A low cloud becomes fog where its base reaches or intersects the surface.
Yes. Low clouds can produce drizzle or light rain, although heavier precipitation is generally associated with thicker and deeper cloud systems.
It can. Visibility may become poor when cloud bases are very low, particularly in elevated terrain where roads, buildings or hills extend into the cloud layer.