Kingfisher City-County Emergency Management Director Steve Loftis announced an excessive heat warning Monday.

The warning has most of Oklahoma surrounded by a “heat advisory.”

Tuesday was expected to be the hottest day in years across the state with dangerous heat from 108 to 115 degrees.

Only a few isolated storms were possible mainly in the north and northwest.

The humidity levels will drop below 20% across western and central Oklahoma so the heat index will be about the same as the air temperature.

However, the fire weather threat was enhanced, especially in southwestern Oklahoma with the very hot, dry conditions.

Criteria for an excessive heat warning is a heat index of 105 degrees or greater that will last for two hours or more.

The general rule of thumb for such an advisory is when the maximum heat index temperature is expected to be 100 degrees or higher for at least two days and night time air temperatures will not drop below 75 degrees.

When the heat index exceeds 90 degrees, heat stroke or heat exhaustion is possible.

A heat index of 103 degrees or hotter means heat exhaustion is likely, heat stroke is possible.

Finally, a heat index of 125 degrees or hotter is extremely dangerous, with heat stroke likely.

A heat warning means that some people can be seriously affected by heat if precautions are not taken.

Studies in Canada, Europe and the U.S. have indicated that mortality begins to increase exponentially as the heat increases or stays above a heat index of 104 degrees. Note: This threshold will be a rare event in the National Weather Service alert. Even the warm summer of 2005 would not have produced a heat warning, the state advisory said.

All residents were advised to be cautious about spending time in the heat with elderly residents most vulnerable, said Loftis.