On Tuesday, parts of country, specifically 18 states were said to be under a heat advisory, warning or watch, according to the National Weather Service. The United States National Weather Service warned residents of the most significant heat wave the region has experienced in at least the last five years.

The combination of hot temperatures and high humidity will combine to create a dangerous situation in which heat illnesses are likely, the National Weather Service warned. This is unusual, said Pat Slattery, spokesman for the weather service. There's no sugar coating anything here.

Affected states included Illinois, Wisconsin, Minnesota, Iowa, Missouri, Kansas, Nebraska, Oklahoma, and South and North Dakota.

Authorities warned those under the heat dome to drink plenty of fluids, stay in air conditioned spaces, out of the sun and to check on relatives and neighbors and said that once the humidity is factored into the mix, it will feel like 110 degrees in some parts of the nation.

Temperatures in places such as Dodge City, Kansas, and Woodward, Oklahoma, were forecast to be above 100 degrees through Saturday. Wichita, Kansas, will see temperatures higher than 100 degrees through Sunday, officials added.

This heat wave is particularly dangerous because many of the areas under its umbrella are not used to prolonged high temperatures and humidity, according to the weather service. Plus the overnight temperatures are not expected to dip low enough to provide any reprieve. The cumulative effects, when it doesn't cool down overnight, you get no relief, Slattery said.

According to the weather service outlook, the central United States from North Dakota to Texas and east to the Carolinas, excluding parts of the Northeast and Southern Florida, will see excessive heat through July 29.