Heat Wave Spreads East, Threatening Millions

A major heat wave that gripped the Midwest is advancing eastward, predicting record-high temperatures for millions. Many areas won’t see relief until the weekend.

Over 160 million people are under extreme heat warnings or advisories ahead of the Fourth of July. For many, it marks the second or third consecutive day of severe heat alerts, urging people to avoid outdoor activities during peak heat.

Triple-digit temperatures are exacerbated by high humidity, resulting in intense heat index readings. Emergency officials emphasize that the heat index, which accounts for humidity, is a better reflection of outdoor conditions than temperature alone.

On Tuesday, the heat index reached 106 in Chicago, 113 near Milwaukee, 103 in Cleveland, and 113 in Southern Illinois. The Weather Service predicts heat index values from 100 to 115 degrees across cities from Kansas City to Boston on Wednesday.

Radley Horton, a professor at Columbia University’s Climate School, noted the significant role of humidity in this heat wave. He explained that high moisture levels cause nights to remain warmer, with minimal temperature variation between day and night.