Dense Smoke in Dickey, North Dakota

May 17 had the poorest air quality ever measured in North Dakota. During the morning hours a cold front entered northwestern North Dakota and progressed across the state through the remainder of the day. Behind the front, north to northwest winds ushered in dense smoke from Canadian wildfires. The smoke had been held aloft for a few days, and was brought to the surface by the winds associated with the cold front. Visibility dropped abruptly to one-half mile or less across much of western and central North Dakota as the dense smoke moved in, with some locations recording visibilities less than one-quarter mile for a prolonged period of time. The Air Quality Index (AQI) pushed well into the hazardous category, which is the highest category, and begins at a PM2.5 concentration of 250.5 ug/m3. The highest hourly concentration reported was 1,041.1 ug/m3 at Hannover in Oliver County, with most other reporting stations in western and central North Dakota registering maximum hourly values well over 700 ug/m3. According to personnel at the North Dakota Department of Air Quality, this smoke produced the worst air quality conditions ever measured in the state. Conditions did improve some from northwest to southeast during the late day and evening, but visibility remained somewhat restricted by the smoke for a few days, and air quality was adversely affected. The event garnered significant media attention. The NWS office in Bismarck received numerous calls about the smoke from both the media and general public.