Generally, during the summer months, dew points have to climb between 55 and 65 degrees before the weather feels sticky and muggy, according to the weather service. Dew points above 65 degrees make the heat oppressive and uncomfortable due to the high level of moisture in the air.

Much of the eastern U.S. and Midwest was facing the threat of severe thunderstorms and heavy rainfall, while heat alerts were issued Sunday for over 50 million people from Kansas to the Carolinas. The big picture: NOAA's Weather Prediction Center issued a Level 3 out of 4 risk for excessive rainfall over parts of the Ohio Valley through Monday morning,