The Stratus Principal Cloud Type (cloud genus) is also in the Low Cloud Family. Stratus often covers the sky with a low gray uniform layer. The cloud content is usually widely dispersed water droplets that are above freezing or super-cooled droplets below freezing. If the temperature is sufficiently cold there may be ice crystals but this is relatively rare and found only in very cold air masses. Stratus does not normally produce precipitation however if it occurs it is in the form of drizzle, small ice crystals, or snow grains.

Stratus often forms from dissipating fog. Stratus may form over land at night due to low level radiative cooling. The fog frequently dissipates from the bottom up after sunrise as the Sun heats the land. The warming air leave an upper cloud layer of Stratus that transitions from Stratus to Stratus fractus or Cumulus before disappearing. Fog is found where a moist stable layer has formed near the ground.