A fast-approaching wildfire has prompted an evacuation order for all of Yellowknife, which has the city's more than 20,000 residents rushing to get to safety. The long lines of people waiting to leave, how Alberta is stepping up to help evacuees, and the urgent plea from Yellowknife Mayor Rebecca Alty to people who insist on staying behind. Several new evacuation orders and alerts are being issued across British Columbia, as officials warn this could be the most challenging stretch yet of the province's wildfire season. How the situation became so dire, and what's expected in the forecast. As emergency crews sift through the ashes of what's left in Lahaina, people are returning to their fire-ravaged community. The fears of an impending economic crisis, the mixed messages to tourists, and the hope to rebuild. Plus: what extreme heat and humidity can do to your heart and brain. Our Jeff Semple goes into a lab to wire up and learn first-hand exactly what happens.