The main weather factors affecting air quality indices during the next several days include:
-lingering moisture is causing low level clouds over southwestern regions and parts of northern forecast areas, while a weak high pressure ridge is causing mainly clear skies in northeastern and some central regions, a cloud band associated with a developing Nor’easter is also causing mainly overcast skies in southern, eastern and the southernmost central regions
-a weak low pressure trough is forecast to move through the US Midwest Wednesday and is forecast to cause partly to mainly overcast skies and scattered light precipitation over portions of northwestern and southwestern regions, while the weak ridge is forecast to cause clearing skies in northeastern and central areas
-partly to mainly overcast skies are forecast to persist through Wednesday in southern and eastern Ontario with a risk of scattered light precipitation developing late in the day as the strengthening Nor’easter tracks northward along the east coast
-light east to northeasterly winds and near seasonal temperatures are forecast
-air quality indices are forecast to generally be in the good category due to low pollutant background concentrations
-an upper level trough is forecast to cause partly to mainly overcast skies across all regions and scattered light precipitation in portions of southern, northern and central areas Thursday, while a high pressure ridge is forecast to build across the US Midwest and is forecast to cause a northwesterly flow and near to below seasonal temperatures
-the northwesterly flow is forecast to keep air quality indices in the good category
-the high is expected to track eastward south of the province and is expected to cause partly sunny skies for most of the day, with increasing cloudiness and scattered precipitation expected through most regions late Friday, except eastern Ontario, due to a weak trough forecast to be over the western Great Lakes region
-a southwesterly flow and near to below seasonal temperatures are expected
-air quality indices are forecast to remain generally in the good category due to low pollutant background concentrations
Air Quality Forecast:
Air quality indices are forecast to remain generally in the good category across the province during the next several days.
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.