Fog ? Light drizzle? Too cold?
I’ve never seen either a police laser or radar based trap operating during even light drizzle or fog conditions. Will these environmental conditions nullify any laser or microwave radar based detection schemes?
How low does the humidity level have to be before radar can be used?
Radar frequencies in the X, K, and Ka bands are pretty strongly absorbed by atmospheric water, so they become usless in heavy rain. Don’t know about humidity, though. A WAG says mere humidity is not enough to deter these radars.
Just high humidity has no effect that I’ve ever noticed. Rain definitely interferes, usually just reducing the range of the signal (how close the target has to be before I get a good reading).
I have no experience with laser speed measuring devices, so I don’t know how those are affected.
I would guess that severe dust storm might also interfere.
So, basically, the conditions that cause police radar to be unusable are the same conditions that you should probably drive slower in.