One of the virtues of oil paint is that you can paint in a drizzle or a downpour. Don’t even think of trying it in watercolor. In 100 percent humidity, watercolor washes won't dry.
Here's the setup I was using for a painting of a storefront scene. The umbrella was a cheap beach umbrella that came with a plastic clamp. It attached to the top of the pochade box. It kept the worst of the water off the painting, but instead an icy river flowed down my neck.
It poured for six hours with no let-up. You can see the painting here in its lay-in stage, drawn in loosely with a bristle brush using burnt sienna thinned with turpentine.
It was fun painting the puddles, but I had a devil of a time with the neon drug store sign, as you can see in the final painting. The neon is an intensely saturated color. But it’s also high in value. It’s impossible to capture in both the intense chroma and the high value in the same single paint mixture.
If you go for the bright red chroma, the value or tone of the paint goes lower, and if you try to capture the lightness, you can’t also suggest the color. Analyzing the photo now after the fact, I suppose the trick would have been to show the bright halo of intensely saturated color directly adjacent to the near-white neon tubes.