Good to moderate air quality expected

Smog Advisory Terminated

The Ministry of the Environment has issued a Smog Termination. For regional details see: Current Smog Terminations.

Weather Summary: Issued on Thursday, September 2, 2010

A weak high pressure ridge over northern Ontario is causing partly sunny skies with light northeasterly winds over northern regions during Thursday, while a frontal zone over southern and eastern Ontario is causing mostly cloudy skies with scattered precipitation developing during the afternoon and with light southwesterly winds over most regions. Temperatures are forecast to continue significantly warmer than seasonal values in all of the forecast regions with continuing high humidity in most regions. The frontal zone is forecast to move northward over northern Ontario as a warm front overnight.

During Friday, a cold front is forecast to move eastward across Ontario. Mostly cloudy skies are expected with scattered precipitation developing over most regions and with southwesterly winds veering to westerly following passage of the front.

During Saturday, a strong low pressure trough is forecast to move eastward over Ontario. Cloudy skies and scattered precipitation are expected with temperatures cooler than seasonal values. Southwesterly winds are expected over southern and eastern regions ahead of the trough, and west to northwesterly winds are expected over northern regions north of the trough.

Air quality indices are forecast to be in the good to moderate categories in southern and eastern regions and generally in the good category elsewhere during Thursday and Friday due to ozone and fine particles. During Saturday, air quality indices are forecast to be in the good category across the province.

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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.