We did it over Pennsylvania when the spring temperature dropped into the frost range over the new tomatoes. They pre sell them so frost would be a big financial loss. We light smoke pots so the smoke shows the inversion level so we know exactly where to blow the warm air down. It was about 50' the last time. It works, the fields we did with three helicopters were completely clear when all the others were white with frost. That night every helicopter in Pennsylvania was in the air.