Good to moderate air quality expected

Weather Summary: Issued on Friday, February 22, 2008

A weak low pressure trough south of Ontario is moving eastward during Friday, spreading light precipitation over southern and eastern Ontario, and mostly cloudy skies with light winds are expected over northern regions. The trough is forecast to move eastward from the province later Friday, followed by partly clearing skies.

During Saturday, another weak trough moving across southern Ontario is forecast to cause some cloudiness and scattered light precipitation, followed by clearing skies and light west to northwesterly winds over most regions as a high pressure region west of the Great Lakes spreads dry air across Ontario.

During Sunday, the high is forecast to be south of Ontario and sunny skies with light southwesterly winds are expected over most regions, while a weak low pressure trough over northern Ontario is expected to cause partly cloudy skies with scattered light precipitation over northern regions.

Air quality indices are forecast to be generally in the good category during Friday and Saturday in all forecast regions. During Sunday, clear overnight skies may allow nocturnal inversions to form by sunrise, and allow local ground level pollutants to accumulate and cause air quality indices in the good to moderate categories in some locations of southern Ontario Sunday morning. Otherwise, air quality indices are forecast to be generally in the good category.

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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.