Summary of Weather Factors affecting Air Quality
The main weather factors affecting air quality indices during the next several days include:
-an upper trough is over most of the forecast area and is causing partly to mainly cloudy skies in addition to a weak weather pattern that is causing foggy conditions in some regions due to calm or light east to southeasterly winds as well as continuing high humidity
-an upper ridge is forecast to build across the regions following the passage of the upper trough Wednesday and partly sunny skies are expected along with some day time cumulus clouds, which are forecast to develop in the afternoon due to lingering moisture
-high humidity and near to above seasonal temperatures are forecast to persist along with light east to southeasterly winds due to the weak weather pattern
-the upper ridge is forecast to weaken and move across the forecast regions Thursday and is forecast to cause partly to mainly sunny skies across most regions for part of the day but increasing cloudiness is forecast to develop for most regions ahead of a low pressure trough forecast to be over Hudson Bay, however mainly cloudy skies are forecast for northern regions while partly sunny skies are expected to persist in most eastern regions
-high humidity and a light southeasterly flow are expected to continue Thursday along with near to above seasonal temperatures
-a deepening low pressure trough is forecast to be over the northern Great Lakes region and is forecast to cause partly to mainly cloudy skies along with showers or thunder showers for most of the forecast areas, except for extreme eastern Ontario, where partly cloudy skies and dry conditions are expected
-increasing humidity along with a south to southwest flow is forecast along with near to above seasonal temperatures for early October
-periods of brisk winds are forecast for most of the forecast area, except for eastern Ontario, where winds are expected to be light
Air Quality Forecast
For Wednesday and Thursday air quality indices are expected to be in the good to moderate categories in southern and eastern Ontario due to light winds and continuing high humidity, which will allow increasing concentrations of fine particles. Ozone concentrations may also cause indices to increase to the moderate category due to partly or mainly sunny skies Wednesday and Thursday. Air quality indices are forecast to be in the good to moderate categories due to high humidity and a southwesterly flow allowing increasing concentrations of fine particles in southern and eastern Ontario.
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.