The Michigan Department of Environmental Quality issued an air quality alert for the Ann Arbor area for Saturday.

This is the fourth alert this year. There also was an alert Friday. The department declared Saturday an action day for elevated levels of ozone. Pollutants are expected to be in the unhealthy range for sensitive groups.

The alerts are issued when ground-level ozone and fine particle pollution exceed levels considered healthy. The department urges people, especially those with respiratory conditions such as asthma, to avoid prolonged outdoor exertion.

The DEQ urges people and businesses to avoid activities that lead to ozone formation. These activities include refueling vehicles, using gasoline powered lawn equipment and using charcoal lighter fluid.

The ozone action day Saturday is in effect for Washtenaw, Genesee, Lapeer, Livingston, Macomb, Monroe, Oakland, St. Clair and Wayne counties.

According to the National Weather Service, Saturday's high is 90 degrees F with partly cloudy skies. Forecasts call for tonight to be mostly cloudy with a chance of a thunderstorm and a chance of rain, then thunderstorms after midnight, with a low of 66. Chance of rain is 60 percent.

For updated weather conditions anytime, visit AnnArbor.com's weather page.