The National Weather Service in Norman has issued a heat advisory for much of Oklahoma today and Monday.

Heat index values are expected to reach 105 degrees across areas near and east of Interstate 35.

Forecasters warn that hot temperatures and humidity can cause heat illnesses.

Tips for staying safe in the heat include drinking plenty of fluids, staying in an air-conditioned room or in the shade, avoiding the sun, and checking on relatives and neighbors.

Those who work outdoors should schedule frequent rest breaks in shaded or air-conditioned environments.

The National Weather Service forecasts heat index values as high as 110 degrees in parts of Oklahoma for the rest of the week.

“The heat index, also known as the apparent temperature, is what the temperature feels like to the human body when relative humidity is combined with the air temperature,” according to the National Weather Service.

Chances for thunderstorms return late Tuesday into Wednesday morning across northern and central Oklahoma.

This article originally appeared on Oklahoman: National Weather Service issues heat advisory for much of Oklahoma