Meteorologists on Saturday alerted millions of residents in Puerto Rico and Texas of potentially dangerous heat conditions, with some areas expecting heat indexes over 110 degrees.

Those warnings, however, are far more localized than the widespread air quality concerns after a smokey haze from Canada’s wildfires plagued the eastern United States earlier this week.

On Wednesday, Thursday and Friday, millions of Americans were under Air Quality Alerts along the East Coast in cities like New York, Philadelphia and Washington, D.C. Some schools switched to remote instruction and residents were told to stay indoors or wear protective face masks outdoors.

At the same time, social justice advocates sounded the alarm about the dangers facing cities’ most vulnerable residents who live without proper shelter and couldn’t easily escape the smoggy air.

Here’s what to know about the weekend weather forecast in the US:

Air quality much improved in eastern US

Air quality along huge stretches of the East Coast has improved since Wednesday and Thursday, when residents faced dangerous levels of pollution from smoke that drifted into the U.S. from hundreds of wildfires in Canada. The concerns were worsened by fires in the U.S. as well.

  • What is the air quality on Saturday? On Saturday, the air had “good” or “moderate” levels of particle pollution along the East Coast’s I-95 corridor, meteorologists said. There may still be some hazy smoke visible in the skies Saturday in major cities like New York and Philadelphia, but it will be in higher levels of the atmosphere, said NWS meteorologist Zack Taylor from the Weather Prediction Center. It should not affect people’s breathing.
  • Why did the air quality improve? Shifting winds have allowed the smoke to be more dispersed, according to meteorologists at the National Weather Service’s Weather Prediction Center.