Meanwhile, in the South, there's an elevated flash flood risk in Alabama, Georgia and Tennessee, where scattered showers and thunderstorms are forecast for Saturday afternoon. Strong, slow-moving thunderstorms could drop rain at 1 to 2 inches per hour.

Canada is battling more than 700 active wildfires across the country, roughly two-thirds of which are burning out of control, according to the Canadian Interagency Forest Fire Center (CIFFC). Smoke billowing from the blazes has blanketed central Canada and the northern U.S., prompting widespread air quality alerts.

Wildfire smoke drifting across the Great Lakes has caused air quality to plunge to hazardous levels in several states, affecting millions of people in major cities.