Did you know that meteorologists use satellites that measure temperature to detect cloud cover at night? That's right, "infrared" or "IR" satellite imagery actually measures the temperature being emitted from the earth. Since clouds usually reside in the colder air above the ground, cloud cover shows up as "colder" temperatures (usually brighter colors) on IR satellite images, while cloud free areas show the temperatures closer to the ground which tend to be warmer (usually gray-ish colors). Infrared satellites work really well at showing cloud cover most of the time, however, when the air near the ground gets as cold as air typically gets aloft IR satellites detect that cold air and it shows up as "cloudiness" on satellite.
The satellite image below is a prime example of bitter cold air showing up as cloud cover. Notice the expansive area of yellowish colors extending from the Dakotas and Minnesota northward across most of southern Canada. That isn't cloud cover, that's just bitter cold air near the surface! When cold air shows up like this on satellite it can allow you to see unique features that sometimes are hard it visualize, such as the pocket of warmer air around Minneapolis, MN, due to the effects of the urban heat island of that city. Also, notice the cold air doesn't make it over Lake Superior, which is still mostly unfrozen and helping moderate the cold air mass. Farther south, the satellite is picking up streak of cloud cover from the central plains east to Missouri and also over the eastern Great Lakes.