The Excessive Heat Warning is in effect until 6 a.m. Monday, while an Excessive Heat Watch will be in effect from Monday evening through Monday evening. The last time the temperature in the city hit 100 degrees was in 2012.
As an example, if the air temperature is 96°F and the relative humidity is 65%, the heat index-how hot it feels-is 121°F.
The Pennsylvania Department of Environmental Protection also has continued to issue a code orange air quality alert for the Lehigh Valley and Berks County.
The heat continues into the week, with temperatures reaching well into the 90s each day.
Meteorologists say the intense heat will be caused by a ridge of high pressure - or a "heat dome". Look for record highs in Massachusetts, Michigan, New York and Vermont this weekend.
A cold front will move south across the area Friday with a better chance of showers and thunderstorms.
An excessive heat warning remains in effect through late Saturday for Chicago as sweltering summer temperatures stick in the area.
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Once temperatures reach 90 degrees, we'll have an official heat wave, as temperatures hit 90 on Friday and Saturday.
Do not leave a pet in a auto: Even with windows rolled down, temperatures inside a vehicle can still be 15 degrees higher than outside, experts say. Persons who have epilepsy or heart, kidney or liver disease, are on fluid restrictive diets or have a problem with fluid retention should consult a physician before increasing their consumption of fluids.
Also, a must: wearing light-colored, light-weight clothing and drinking plenty of water.
Do not forget to check in on elderly neighbors and those with breathing issues. In these conditions, people should minimize sun exposure between 10 a.m. and 4 p.m. Cool down with water activities.
Cities across the region, from the Mississippi River to the East Coast, have set up cooling centers to keep people out of the unsafe heat.