The National Weather Service advisory is in effect from 11 a.m. to 8 p.m. for multiple counties, including Perry, Dauphin, Lebanon, Cumberland, Adams, York and Lancaster. The heat index is expected to range between 100 and 104 degrees, with some isolated areas potentially feeling even higher temperatures.

The Heat Advisory has been extended through Tuesday of next week due to high temperatures in the mid-90s, with heat indices topping out in the 100 to 105° range, but change is coming with a shift in the summer ridge and the development of a trough across the East,

The Lehigh Valley will be under a heat advisory from 10 a.m. until 9 p.m. Regions to the south, such as Bucks County and Philadelphia, will be under an extreme heat warning then. It will feel close to 105 in those areas, according to forecasters.

The heat dome won't dissipate soon. Dangerous heat is expected across parts of the Central and Southeast. through July, the weather service says. High temperatures will reach 100 degrees from Texas to western Tennessee almost every day for a week or two, AccuWeather said.

The Detroit Health Department provided tips for staying safe when the temperatures climb: Limit time outside between 8 a.m. and 9 p.m., when it tends to be the hottest; Monitor for signs of heat exhaustion and heat stroke, such as nausea, confusion, rapid or slowed heart rate.