The Maryland Department of the Environment has issued an air quality advisory for June 20, the first day of summer.
On top of the soaring temperatures and humidity, officials forecast an air quality index of 106-in the "orange" or "unhealthy for sensitive groups" range because of high levels of ozone.
On Wednesday and Thursday, hot and humid conditions with light, west-northwesterly winds will cause ozone and fine particle levels to rise, according to the state agency. Fine particles are expected to remain in the moderate range, according to the agency's forecast.
A cold front is forecast to roll into the region on Friday, which may produce cloud cover and thunderstorms. A moderate air quality index is expected to result after the front passes through later in the day on Friday, according to the state Department of the Enviroment.
Updated air quality information and forecasts are available through the state's Air Quality Hotline at 410-537-3247.