Driving through the winter in northeast Wisconsin is a challenge. Keeping your truck clean through that winter is an even bigger challenge. It is rare for me to get my truck washed while on the road. I do like to get it washed when any maintenance work is done. I will also get it washed if I am using it for a Freightliner event, like an open house or a local truck show. Really I think that my blue truck does not look too bad dirty, but it looks great clean.
It has been told to me by enforcement officers that they are more likely to pull a dirty truck around back than a clean one. To them it is a sign. The truck may not be properly maintained. I know that enforcement officers might choose you for a variety of reasons. They might see a marker light out. One of your mud flaps might be torn or missing. These officers are not stupid. They learn. They are constantly looking for signs of more serious violations. Why not just avoid the unwanted attention and wash your truck.
Clean is not just the outside of your truck. Keep any objects off of your dashboard. I had a co-worker ask me how often I got pulled around back. "I don't know maybe a couple of times per year, if that." He was stunned. He told me that he was constantly getting "harassed". We drove for the same company. Our trucks were similar. They each got washed every other weekend. The only difference was that he had "stuff" piled up on the dash. I politely mentioned that might be the issue. He just said that was stupid. I replied with "Who cares if it is stupid? He just grunted and walked away. I wonder if he ever did clean off that dash. I asked an officer about that once. He agreed that a full dash is a sign of other issues and it definitely could be a factor.
It isn't complicated. I don't think officers expect a clean truck in the days following a snow storm. They get that. They can also tell if a truck has not been washed in months. That makes me wonder how the truck has been maintained. I would imagine that the same though goes through the mind of the officer.