It goes into effect at 11 a.m. Thursday and lasts until 8 p.m. on Friday.
The heat and humidity will make the temperature feel like we're in the triple digits both days.
Because of the dangerous heat, the School District of Philadelphia plans to dismiss 52 schools early on the last day of class.
52 Philadelphia schools to dismiss early Thursday due to extreme heat
Gusty storms swept through the area Wednesday evening, bringing rain, thunder and lightning.
There is also a chance of some storms forming in the evening and nighttime hours on Thursday as well.
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Saturday will feel better. While it will still be hot, it will be less humid.
Next week is expected to drop back into the 80s.