Here's why:
* Nimbostratus clouds are dark gray, thick, and often cover the entire sky. They are associated with steady, persistent rain or snow.
* The prefix "nimbo" means "rain" in Latin, indicating their precipitation-producing nature.
* Because they are so dense, they can completely block out sunlight, making the day seem gloomy and overcast.
Other clouds can also be thick, but they are less likely to completely block out sunlight:
* Cumulonimbus (thunderstorm clouds) can be very tall and dense, but they usually have gaps in their structure, allowing some sunlight through.
* Altostratus clouds are gray and sheet-like, but they are generally thinner than nimbostratus clouds.
Let me know if you'd like to know more about different cloud types!
