Good to moderate air quality expected

Weather Forecast: Issued on Friday, November 21, 2014

The main weather factors affecting air quality indices during the next several days include:

Friday:
-a strong high pressure ridge moving eastward across Ontario and the eastern US is causing continuing cool temperatures and partly or mostly sunny skies over most regions, except for cloudiness over northern regions and lake-effect cloudiness with scattered precipitation east of the big lakes
-winds are forecast to be west to northwesterly during the morning and west to southwesterly during the afternoon as the ridge axis moves eastward
-pollutant concentrations are not expected to increase significantly and air quality indices are forecast to remain in the good category

Saturday:
-the ridge is forecast to be east of Ontario and a low pressure trough is forecast to move over northwestern Ontario, resulting in a southwesterly flow with temperatures moderating to seasonal values
-winds are forecast to be southwesterly and skies are forecast to be mostly cloudy with scattered light precipitation possible over all of the forecast regions
-pollutant concentrations are not expected to increase significantly and air quality indices are forecast to remain in the good category

Sunday:
-a weak high pressure ridge is forecast to be over eastern Ontario during the morning and a strengthening low pressure trough is forecast to be west of the Great Lakes
-winds are forecast to be south to southeasterly and upper level winds are forecast to be southwesterly, causing increasing warmth and humidity over all of the forecast regions
-the increasing temperatures and humidity may be accompanied by increasing concentrations of fine particles, but air quality indices are expected to remain mostly in the good category

Air Quality Forecast:
Air quality indices are forecast to remain mainly in the good category across the province during Friday, Saturday and Sunday.

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Smog, comprised of Ozone (O3) and/or Fine Particulate Matter (PM2.5), is primarily a summer phenomenon, occurring mostly in southern Ontario; however, PM2.5 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.