Triple-Digit Heat Is Closing In on 200 Million Americans

The heat dome is here, bringing scorching temperatures to about 200 million Americans in the days leading up to the Fourth of July holiday weekend. Read on for a more precise look at the timing and heat associated with this sprawling zone of high pressure setting up shop across much of the central and eastern U.S.

Heat Dome Building Over Central U.S. to Start the Week

An expansive heat dome is spread across the central U.S., forecast to bring temperatures well into the 90s to millions in its path. Several of the nation's largest metro areas will feel the impact of this heat wave, including New York City, Philadelphia, Washington, D.C., Chicago, St. Louis, and more.

In addition to the scorching air temperatures, rising humidity levels will amplify the heat. Real feel readings will surpass the century mark in many areas as dangerous conditions encompass more than two dozen states.

Dew point readings will climb into the 70s for many parts of the country. This reading represents the saturation temperature in the air. For context, most people would consider it noticeably humid with dew points in the 70-degree range. Although this is a typical occurrence during the summer in the steamy South, those in the Midwest and the Northeast are not acclimated to this type of humidity.

The longevity of this heat wave will compound its impacts. For instance, Chicago is bracing for at least four to five straight days of readings of 90 degrees or higher. Typical highs in the Windy City in early July hover in the mid 80s. It will be even toastier to the south. St. Louis will see readings near 100 degrees for at least eight consecutive days.

Although a few locations within the heat dome may set new record highs, the most notable records may come in the overnight hours. Forecasters are predicting that some of the larger urban areas may not see readings fall below 80 degrees at night during the peak of the heat wave.

It is natural for urban areas to retain heat even in the overnight hours due to the proliferation of pavement, concrete, and brick. Known as the urban heat island effect, these surfaces inherently absorb the sun's energy during the day and then slowly release it back into the air when the sun goes down, keeping the temperatures elevated even under the cover of darkness.

The heat and humidity will move from west to east as the week progresses. While temperatures will begin to moderate slightly in the central U.S. by the time that the Fourth of July rolls around, the eastern U.S. could still be under the gun for the sizzling weather on the holiday.