Story highlights Some of the hottest temperatures of the summer are expected this week

Heat kills more people in the United States than all other natural disasters combined

(CNN) The dog days of summer are hitting hard this year, and forecasters warn that some of the hottest temperatures of the season may sear a large portion of the United States this week.

Very high humidity is expected to accompany the heat, especially in the Midwest, and that moisture -- combined with the high temperatures -- will create what's known as a "heat dome" over most of the country. Only the Northwest will be spared.

Those conditions could be deadly. Forecasters say the heat index, which measures what the temperature really feels like when you add in the humidity -- the summer equivalent of the winter wind chill -- will likely reach the dangerous category, increasing the risks of heat exhaustion, heat stroke, and death.

What it actually feels like outside when you take into account the humidity and high temperature.

Cities such as Des Moines, Kansas City, St. Louis, Minneapolis, Oklahoma City and Chicago are expected to see temperatures nearing or exceeding 100 degrees -- and when humidity is added in, the heat index may rise to a dangerous 120 degrees.

Heat is one of the deadliest weather events, killing hundreds of people every year. Extreme heat results in even more heat-related illnesses.

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