Good to moderate air quality expected

Weather Summary: Issued on Thursday, July 2, 2009

A low pressure region over southern Ontario during Thursday is causing cloudiness, scattered precipitation, and temperatures cooler than seasonal values in all of the forecast regions.

During Friday, the low is forecast to move slowly eastward from Ontario and cause continuing unsettled weather conditions, and a weak high pressure ridge is forecast to develop west of the Great Lakes and cause clearing skies over southwestern Ontario and light westerly winds over all of the forecast regions.

During Saturday, the low is forecast to be over southern Quebec and the ridge is forecast to move eastward over the Great Lakes region and cause light northwesterly winds with partly or mostly sunny skies over most regions, except for cloudiness and scattered precipitation continuing over eastern regions.

Air quality indices are forecast to be generally in the good category during Thursday and Friday in all forecast regions. Saturday's air quality indices are forecast to be mostly in the good category, except for indices increasing to the moderate category in southwestern regions.

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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.