It is simply worth it every time that you go out to paint.....even if there is a heat warning or an imminent thunderstorm. We had a heat warning on Monday and it was totally oppressive by 8:30 in the morning but I went anyway. When I got to the boat landing it was hot but there was a breeze of about 20mph. and it was wonderful! The humidity made the landscape seem more solid somehow (without diminishing the color which it does sometimes)...........the water was at my back when I painted this and I focused on that tiny little stripe of green/coolness that appears between the horizontal tabletop of the grasses and the vertical of the trees!