Long-range Transport of 2026 Canadian Wildfire Smoke into the United States (July 14-19, 2026)

Despite a slow start to the 2026 biomass burning season across Canada, devastating wildfires erupted in central Canada in mid-July. The same heat dome that impacted the United States created hot and dry conditions over Ontario during the first week in July that primed the land surface for dangerous fire weather conditions. As is typically the case for the region, lightning strikes then ignited wildfires in the drought-ridden area of Ontario. Wildfires release plumes of smoke that contain toxic gases and fine particulate matter (PM2.5), both of which are harmful to human health. Wildfire smoke can travel hundreds of miles, causing widespread impacts well beyond the source of the smoke, as shown in the animation.

The animation demonstrates the transport of smoke within the GEOS model using the aerosol optical depth (AOD) for brown carbon. Brown carbon is an aerosol tracer representing the organic matter emitted by wildfires, which tends to absorb more sunlight than organic matter emitted by anthropogenic sources such as power plants. A larger value for AOD typically indicates a higher loading of aerosol particles. On July 14, a high-pressure system stationed over the central United States positioned the jet stream, or a fast-moving steering current for upper-level air flow, such that the smoke was able to travel from Ontario into the northeastern United States. Roughly two days later, ushered in by a frontal system, the smoke reached densely populated areas of the United States. The downward motion of the cold air behind the front kept the smoke near the surface rather than aloft.

The daily average concentrations of fine particulate matter (PM2.5) in the Baltimore-Washington, D.C. area on July 17, 2026, neared 200 micrograms per cubic meter (µg/m3), prompting Code Purple air quality alerts in the region. Smoke was still prevalent the following morning, creating a widespread haze due to increased relative humidity until the aerosol particles were washed out of the atmosphere by severe thunderstorms. With the wildfires still raging and a consistent upper-level flow, smoke continued to be transported into the northeastern United States. The meandering pattern of the jet stream resulted in waves of smoke oscillating latitudinally for the next few days.