The warning went into effect at noon on Wednesday and will remain in effect until Thursday at 7 p.m.
The heat wave is expected to last through at least Friday.
A thunderstorm watch has been issues in the western part of the state.
Central Pennsylvania is under the heat warning with much of the remainder of the state under heat watches and advisories.
The heat index values are expected to be between 104 and 110 degrees Fahrenheit.
The National Weather Service is urging the public to take steps to protect themselves from the heat including the following:
- Drink plenty of fluids
- Stay in an air-conditioned room
- Stay out of the sun
- Avoid strenuous activities
- Wear lightweight and loose fitting clothing
The NWS reminds the public not to leave children and pets unattended in vehicles under any circumstances, and suggest checking in on housebound and elderly neighbors.
If you experience symptoms of heat stroke call 911.
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