The main weather factors affecting air quality during the next several days include:
-a strong arctic high pressure ridge moving southeastward over the province is cause clearing skies over most of the forecast regions (except for cloudiness persisting south of Lake Huron), gusty north to northwesterly winds (except for light winds over northwestern forecast regions near the ridge axis), and temperatures decreasing below seasonal values
-air quality indices are forecast to be in the good category due to strong ventilation and dispersion conditions in the cold northwesterly flow
-the high pressure ridge is forecast to be over eastern Ontario while a low pressure trough is forecast to move eastward over northern Ontario
-cloudy skies are expected over most regions, except for partly sunny skies over eastern regions, and light scattered precipitation is expected over some regions
-cold temperatures are expected with light winds over most regions except for westerly winds over eastern regions and increasing southwesterly winds over southern Ontario during the afternoon
-concentrations of pollutants are not expected to increase significantly and air quality indices are expected to remain mostly in the good category, but pollutant concentrations could increase and cause increasing indices in locations where winds remain calm or light
-a strong arctic high pressure ridge is forecast to spread across northern Ontario and a low pressure trough is forecast to move eastward over the eastern US
-mostly sunny skies are expected over northern, central and eastern regions and cloudy or partly cloudy skies are expected over southern Ontario
-north to northeasterly winds are expected with temperatures significantly colder than seasonal values
-good ventilation and dispersion conditions in the cold northerly flow are expected to result in air quality indices in the good category
Air Quality Forecast:
Air quality indices are forecast to remain generally in the good category across the province during the next several days, but indices may increase toward the moderate category during Saturday in some regions where winds become light or calm.
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.