Ah, the joys of plein-air painting in Ohio. If the bugs aren't biting, the sky is threatening. But I wouldn't change a thing about it!
It just so happens that my last several Saturday morning paint-outs have coincided with cloudy days, which is what prompted me to paint super fast. All of these are one-hour (or less) paintings. I seem to be able to move faster with the palette knife than with the brush, so I used one of my favorite tools for all of them. It's a great exercise if you've never tried it. It really forces you to focus on your big shapes and get to the essence of your subjects. But I still paid attention to harmonizing the color relationships.