These photos were taken just one day apart, showing how quickly Toronto's sky went from clear to smoky. Smoke from forest fires in northwestern Ontario is causing poor air quality and reduced visibility for much of southern Ontario, according to Environment Canada, which says the conditions may last until Friday morning. The agency is urging people to 'reschedule or cancel' outdoor activities. »»» Subscribe to CBC News to watch more videos: http://bit.ly/1RreYWS For breaking news, video, audio and in-depth coverage: https://www.cbc.ca/news Follow CBC News on TikTok: https://www.tiktok.com/@cbcnews Subscribe to CBC News on Snapchat: https://bit.ly/3leaWsr Subscribe to CBC News on WhatsApp: https://www.whatsapp.com/channel/0029Vb6MSjH9Bb63S9tbQa1Y Download the CBC News app for iOS: http://apple.co/25mpsUz Download the CBC News app for Android: http://bit.ly/1XxuozZ »»»»»»»»»»»»»»»»»» For more than 80 years, CBC News has been the source Canadians turn to, to keep them informed about their communities, their country and their world. Through regional and national programming on multiple platforms, including CBC Television, CBC News Network, CBC Radio, CBCNews.ca, mobile and on-demand, CBC News and its internationally recognized team of award-winning journalists deliver the breaking stories, the issues, the analyses and the personalities that matter to Canadians.