Stratus clouds form flat gray layers that can cover the whole sky for days.

The longer version

Flat gray stratus layers form when a broad sheet of moist air is lifted gently over a large area and cools slowly. Because the lifting is weak and spread out, the condensation arrives as a wide horizontal blanket rather than separate heaps. The layer often sits low, with its base close to the ground.

Such cloud can linger for days while the air beneath it stays calm and the supply of moisture continues. The thickness of the sheet decides whether the result is dull overcast skies or a light drizzle. Stronger uplift or a change of air mass is usually needed to break it up.

Where this entry sits

Clouds, wind, rain, and storms shape daily life in ways that most people barely notice. This collection explains snow, lightning, rainbows, the turning seasons, temperature, the instruments forecasters rely on, and scraps of old weather lore. The full list sits on the Weather and Climate page, where every entry is listed in order.