[rwoerz]

"Nachts ist kälter als draußen." Not sure if this really works in English: "At night is colder than outdoors."

[albert_e]

I wonder if there is an element of implied location (wherever the speaker is usually present physically "at night" -- presumably at home) and time (usually day time for "outdoors") that might make the sentence meaningful and good enough for every day communication?

[deltaonefour]

It could work.

"The temperature at night is much much more colder then the temperature outside.