The smoke from the wildfires in southern and central Canada have provided more of a hazy sky the last few days over the Midwest, Plains and Great Lakes. But the smoke Tuesday has become a little more problematic, especially in Minnesota and Wisconsin, as skies have filled with quite a bit of smoke down closer to the surface. This has actually reduced visibility for residents in northern and central Wisconsin, prompting Air Quality Alerts to be issued. This means higher concentrations of fine particulate matter could reach unhealthy levels for the more sensitive group levels. Those include children, elderly people and individuals with respiratory and cardiac problems.
A cold front, known as a back door cold front because it is coming more from the northeast, is quickly moving through Wisconsin and down Lake Michigan. The air behind the front is a little more dense causing it to sink down towards the surface. The last few days the smoke from the wildfires has remained well above the surface, in the upper levels of the atmosphere. But the sinking air behind the front is pulling that smoke down closer to the surface.
Higher concentrations of the smoke will be noticed further north but hazy, and for some smoky, skies are likely to impact areas further south; this includes northern Illinois later tonight. The cold front is expected to pass through between 8pm and 10pm Tuesday. As it does the wind will be shifting around to the northeast. This is when we could see a little more haze/smoke fill our skies, as well as potentially even smelling the smoke. Some of that could carry over into Wednesday morning but the impacts will be a little lower at that time. With the upper level winds shifting more to the west and southwest later in the week, the haze and smoke won’t be as much of an issue.