Good to moderate air quality expected

Weather Summary: Issued on Friday, March 12, 2010

A strong high pressure ridge over Quebec and a low pressure trough south of the Great Lakes during Friday are causing easterly winds over Ontario with cloudiness over most regions and scattered precipitation over some southern Ontario regions, except for partly sunny skies over some eastern Ontario regions.

During Saturday, increasing and gusty easterly winds are expected with cloudy skies over most regions and some precipitation over southern Ontario as the low moves eastward over the eastern US and the eastern ridge spreads across northern Ontario.

During Sunday, the high is forecast to strengthen over northern Ontario as the low pressure trough moves eastward to the Atlantic coast. Northeasterly winds are expected over all regions with clearing skies over northern regions as the cloudiness and moisture move southeastward. Temperatures are forecast to continue significantly warmer than seasonal values with the polar jet stream continuing to be north of the province.

Air quality indices are forecast to be generally in the good category in all forecast regions during the next several days. Sunday's air quality indices may increase to the moderate category in some northwestern forecast regions where skies become sunny due to ozone during the afternoon.

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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.