Good to moderate air quality expected

Weather Forecast: Issued on Friday, December 19, 2014

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

Friday:
- a high pressure ridge over Ontario is cause partly clearing skies over most regions, except for sunny skies over northwestern regions, with diminishing northwesterly winds and temperatures near seasonal values
-pollutant concentrations are not expected to increase significantly in the cooler northwesterly flow and air quality indices are forecast to remain generally in the good category

Saturday:
-the ridge is forecast to be over southern Ontario and all of the forecast regions and to cause light winds and partly or mostly sunny skies over most regions, except for increasing cloudiness over southwestern regions ahead of an upper-level trough which is forecast to move over the southern Great Lakes region
-pollutant concentrations are not expected to increase significantly and air quality indices are forecast to remain generally in the good category

Sunday:
-the ridge is forecast to move eastward over eastern Ontario and to cause partly sunny skies over most regions with generally seasonal temperatures for late autumn
-winds are forecast to be light or calm
-the light or calm winds and weak ventilation and dispersion conditions may allow concentrations of fine particles to increase and cause air quality indices to increase to the moderate category in some regions

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