When it's not safe to drive, it's not safe to drive.

I've been in zero-road-speed whiteout conditions several times. The only move to make is to the side of the road without getting stuck, and turning on your flashers.

Low-light cameras would not have worked. Sonar would not have worked. Infrared would not have worked.

If you have multi-return lidar, you can see through certain occlusions. If the fog/rain isn't that bad, you can filter for the last return and get the hard surface behind the occlusion. The bigger problem with rain is that you get specular reflection and your laser light just flies off into space instead of coming back to you. Lidar not work good on shiney.