Smoke from wildfires burning in three Canadian provinces is spreading into the U.S. Upper Midwest, stirring memories of the severe pollution that drifted south from Canada two years ago during that country's worst fire season on record.

Haze from Canadian wildfires is seen over Lake Michigan as a person runs along the shoreline Monday in Chicago. Wildfires burning in British Columbia, Alberta, Saskatchewan, Manitoba and Ontario are affecting parts of the United States. (Joshua Lott/The Washington Post)

You may notice a bit of a haze in the air this week. In part, it’s coming from central Canadian wildfire smoke. We’re keeping a close eye on it, but unless you are unusually sensitive to fine airborne particles,