In Colorado the weather is so random, that it makes me not even want to bother. My truck is filthy since last week's snowstorm. It's been clear and sunny the last few days, but the meltoff from the snow keeps the roads soaking wet in many areas, so even if I washed it it would be dirty again in about an hour. Now we have another storm coming Sunday or Monday.
I wash my truck after the bigger storms just to get the mag chloride de-icer off of my paint and undercarriage. I don't do it to keep the truck totally clean, because that's impossible lol.