The main weather factors affecting air quality during the next several days include:
-a low pressure trough is centred over northern Ontario causing partly or mostly cloudy skies across northern regions, while elsewhere partly or mainly sunny skies are occurring courtesy of a high pressure ridge over eastern Ontario and southern Quebec
-the centre of the low is projected to move northeasterly into northern Ontario and northern Quebec and is expected to result in partly or mainly cloudy skies to continue for northern regions, while becoming increasingly cloudier for central regions with the risk of showers or thundershowers mainly for northern regions; the ridge is forecast to move southeastward and to cause partly or mostly sunny skies for southern and eastern Ontario most of the day
-southerly winds with near to above seasonal temperatures are anticipated
-air quality indices are forecast to be in the good to moderate categories across the province due to the generation of ozone caused by partly or mainly sunny skies and calm or light winds, which may allow concentrations of fine particles and ground level pollutants to increase
-the low is expected to migrate into northeastern Canada, while a cold front associated with the low is forecast to gradually track southeastwardly across the forecast areas and is projected to result in partly or mainly cloudy skies with showers or thundershowers
-ahead of the front high humidity and southwesterly winds are expected, while the passage of the front is forecast to cause winds to veer from the west to the northwest and is also expected to cause humidity to decrease
-temperatures are projected to be mainly above seasonal values for most regions, except northern regions, where near to below seasonal temperatures are forecast
-air quality indices are forecast to be in the good to moderate categories for southern and eastern regions due to calm or light winds and high humidity allowing concentrations of fine particles and ground level pollutants to increase, while elsewhere indices are expected to generally be in the good category
-the cold front is forecast to continue tracking southward from the province and is expected to result in partly or mainly overcast skies for some southern and eastern regions, while elsewhere mainly sunny skies are projected to occur courtesy of an area of modified arctic high pressure, forecast to build in behind the front over the province
-north to northeasterly winds are forecast to occur along with near to below seasonal temperatures
-northerly winds are anticipated to keep air quality indices generally in the good category
Air Quality Forecast:
For Friday, air quality indices are anticipated to be in the good to moderate categories across the province. Air quality indices are forecast to be in the good to moderate categories in southern and eastern Ontario Saturday, while elsewhere indices are projected to be in the good category. For Sunday, air quality indices are forecast to be generally in the good category.
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.