A low, gray, featureless layer that covers the sky like a blanket is stratus. These clouds sit close to the surface, often only a few hundred meters above the ground, and can extend for hundreds of kilometers horizontally.

Stratus forms in stable air when moist air is cooled to saturation, frequently by gentle lifting or by contact with a cold surface. Light drizzle or mist often falls from stratus. When the cloud intersects the ground it becomes fog.

The uniform gray appearance produces dull, overcast days. Visibility below the cloud is usually good unless drizzle is occurring. Stratus can persist for long periods until a change in air mass or an increase in wind breaks up the layer.

Pilots regard low stratus as a ceiling that can restrict visual flight operations.