If you switch to non-lidar mode for unfavorable condition, why don't just use the non-lidar for all conditions. A system that is safe for unfavorable conditions is likely to be the system that is safe for all conditions.
Because lidar allows faster travel in the modes where it works. When there is heavy rain/snow the only safe speed is very slow anyway. When roads are clear and dry I really want my car to go faster than the elderly walk (I walk faster than that normally), and lidar may be required for that mode.
Just like in cooking you can use meat cleaver and a paring knife or in a network you use switches and routers.