Good to moderate air quality expected

Weather Summary: Issued on Friday, July 30, 2010

A high pressure ridge over Ontario during Friday is causing mostly sunny skies with light northwesterly winds, except for southwesterly winds developing over the northwestern forecast regions, and with temperatures continuing cooler than seasonal values.

During Saturday, the ridge is forecast to move eastward over southern and eastern Ontario and a weak low pressure trough is forecast to develop over the central Great Lakes region. Partly sunny skies with increasing cloudiness are expected over southern and northern regions, and mostly sunny skies are expected over eastern regions. Light southwesterly winds are expected with temperatures moderating toward seasonal values.

During Sunday, the low pressure trough is forecast to move eastward over southern Ontario, causing some cloudiness over most regions and scattered precipitation over some regions. Temperatures are forecast to be near seasonal values, except for increasing warmth and humidity over southwestern Ontario.

Air quality indices are forecast to be in the good to moderate categories in some regions of southern Ontario during Friday and Saturday, and generally in the good category elsewhere. Sunday's air quality indices are forecast to be in the good to moderate categories in southern and eastern Ontario and generally in the good category elsewhere.

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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.