Washington, Nowata, and Osage Counties, are under a heat advisory through Friday evening as temperatures and humidity levels remain high.
 
The heat advisory covers the eastern two-thirds of the state. Forecasters say high temperatures could reach the low 100s Thursday and Friday, with heat index values of 105 degrees to 108 degrees.
 
Forecasters say the heat and humidity will persist through Saturday night when there's a chance for thunderstorms.
 
Emergency officials in Oklahoma say they've responded to dozens of calls in the past week for heat-related issues. Emergency Medical Services Authority says people should stay hydrated, wear light-colored clothing and limit time spent outdoors, if possible.