Stratus clouds - rain or snow clouds
I like this view of the tops of these low stratus clouds, I snapped it just before the plane slipped through them. It is strange to fly above these clouds being in the sun and then suddenly be in the rain when the plane drops below them. Stratus means "sheet-like", I tell my students to think of the sheet they sleep under on their bed, it is low, flat, and covers a lot of area like these clouds. Stratus clouds are usually no higher than a mile above the ground, but they can cover an entire state or even a large region of the country. They bring precipitation in the form of rain or snow.