A heat dome occurs when high pressure acts as a lid on the atmosphere and as hot air tries to escape the lid forces the air to sink, according to CNN.
This causes the air to warm even more as it sinks.
Forecasters predict that the heat index will likely reach the dangerous category, creating deadly conditions.
People could also suffer from heat exhaustion and heat stroke.
Weather experts have said that ‘corn sweat could be contributing to the hot weather.
Planted corn fields in the Midwest have been known to boost dew points, according to CNN.
The corn crops pull moisture from the soil and some of that moisture escapes into the atmosphere, forming a very high ‘pool’ of moisture.
In the Midwest, these conditions can lead to very high heat index values.
Arizona will be the hardest-hit, peaking at 116 degrees, according to long-range predictions by the National Weather Service.
If those predictions bear out practically the entire country will be suffering from the unusually warm summer weather, with only the Pacific Northwest escaping relatively unscathed.
The build-up is expected to begin Sunday, as the heat currently centered on the southwest states – and the California and Arizona border – flows quickly out across the country, hitting the western reaches of the Midwest hard.
Cities such as Des Moines, Kansas City, St Louis and Oklahoma City are expected to see temperatures nearing or exceeding 100 degrees.