Here is a very interesting video from the What Tesla Autopilot really sees series from the greentheonly channel. This video presents Autopilot image recognition (Firmware 19.8.1) during a night storm.
As you can see from the seven cameras, the overall situation on the highway is way simpler than in the city, where the record is swarmed with objects. Here, just several objects were identified and marked.
On the other hand, the night and storm makes image recognition more demanding for Autopilot and it seems that the view is disturbed from time to time by intense rain.
It’s probably safe to assume that just like in case of humans, it will be more difficult for Autopilot to drive safely at night, in rain or snow.