There isn’t one fixed setting—snow at night depends on the look you want. The main issue is that auto exposure often tries to make the scene average to middle gray, which can leave snow too dark or blow out the streetlights.

A good approach is to avoid full auto and use either:

• manual mode, or
• exposure compensation

General guidance:

• For a darker, moodier low-key look: use less exposure than the camera suggests (for example, a faster shutter speed).
• For brighter, whiter snow: use more exposure than the camera suggests (for example, a slower shutter speed).

Start by taking a test shot in auto or aperture priority, then review the camera’s chosen shutter speed, aperture, and ISO. Use that as a baseline and adjust from there depending on whether you want the snow brighter or the whole scene moodier.

Because light is limited, expect slower shutter speeds and/or higher ISO. If your shutter speed gets too slow, use a tripod or other stable support. Fresh snow is reflective, so if you experiment with flash, check results carefully.