Usually has to be 80 or higher. The hotter the temperature, the more likely elevated levels of ozone will occur. Higher temperatures enhance the ozone formation chemistry and increase the evaporative emissions of volatile organic compounds. Winds out of the south-southwest typically bring warmer weather to West Michigan, or transport ozone from upwind locales, like Chicago. At higher wind speeds, emissions are diluted or dispersed, however ozone can still be transported from other locales.
Dry weather allows ozone to remain in the air.
Widespread rain will cleanse the atmosphere of ozone, therefore scattered showers and thunderstorms are not enough to completely eliminate ozone.