Forty million people were under heat alerts Tuesday across the Central and Southern U.S. as a hot and sultry air mass led to dangerously hot conditions.

Houston hit 100 degrees Sunday and Monday, Dallas has reached 101 on three days since Friday, and Oklahoma City saw a high of 103 degrees Monday. Many locations set daily records for high temperatures, as Atlanta did three days in a row.

It’s an impressive heat wave, but it’s nothing compared to what Europe endured two weeks ago when all-time national records fell in at least half a dozen countries, nor are many all-time daytime high temperature records being broken.

Then why does it feel so awful?

It’s all about the heat index  […]