Good to moderate air quality expected

Weather Summary: Issued on Friday, May 9, 2008

A weak high pressure ridge developing over Ontario is causing partly or mostly sunny skies over most regions during Friday, and a low pressure trough south of the province is causing some cloudiness over southern Ontario and causing east to northeasterly winds over southern and eastern Ontario. A weak mid-level disturbance is causing some cloudiness over northern regions.

During Saturday, mostly sunny skies are expected by afternoon with light north to northwesterly winds over most regions and seasonal temperatures.

During Sunday, a strong low pressure storm is forecast to develop near the southern Great Lakes region and cause increasing cloudiness and precipitation over southwestern Ontario, with increasing east to northeasterly winds over all regions. Generally sunny skies are expected over central and eastern regions.

Air quality indices are forecast to be in the good to moderate categories in most forecast regions under mostly sunny skies due to afternoon ozone generation under the strong May sunshine. Sunday's air quality indices are forecast to be in the good category in southern and northwestern regions where skies become cloudy by afternoon, and in the good to moderate categories elsewhere where skies remain mostly or partly sunny.

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Smog, comprised of ozone and/or PM_2.5, is primarily a summer phenomenon, occurring mostly in southern Ontario; however, PM_2.5 can elevate smog levels during all months of the year. For this reason, the ministry reports the AQI hourly, seven days a week; and continues to provide air quality forecasts daily.