What is an Air Quality Forecast?

An Air Quality Forecast is a prediction of the quality of the air in the future.

The Ministry wants to give Ontario residents as much notice as possible if it looks as though a smog day is on the way. So the Ministry will issue a 3-day outlook or a smog prediction for today, tomorrow and the third day. Since smog days are tied to weather, our meteorologists keep a close watch on short and long-range weather forecasts, and continually study air quality information concerning Ontario and neighbouring U.S. states.

Air quality forecasts are issued in three descriptive categories

• Good means the Air Quality Index (AQI) reading is expected to range from 0 to 31.
• Moderate means the AQI reading may range from 32 to 49
• Poor means the AQI reading is expected to be at least 50. If poor readings are predicted to be sustained over a period of time and over a wide area, then a Smog Alert is issued for that area.

There are two kinds of Smog Alerts that could be called. A Smog Watch is issued when there is a 50 per cent chance that elevated smog levels are forecast to occur within the next three days.  A Smog Advisory is issued when there is a strong likelihood that elevated smog levels are forecast to occur within the next 24 hours, or it can be issued immediately if widespread, poor AQI readings occur, and weather conditions conducive to the persistence of such levels are expected to continue for several hours.