Here's why:

* Altitude: Altostratus clouds are found at middle levels of the atmosphere, typically between 6,500 and 20,000 feet (2,000 to 6,000 meters). Your range of 5,000 to 20,000 feet falls within this range.

* Appearance: They are known for their grayish, sheet-like appearance that often covers the entire sky.

* Transparency: Altostratus clouds can be thin enough to allow the sun or moon to shine through as a hazy disk.

Let me know if you have any more questions about clouds!