Crews tearing apart a 1.5-acre pile of coal mine refuse that has been smoldering for two decades recently uncovered a section which measured 300 degrees Fahrenheit.

The temperature in New York City has reached 100 degrees as the eastern U.S. sweltered under an extreme heat wave.

A persistent “heat dome” has settled over the eastern U.S., triggering heat advisories and triple-digit heat index values across Kentucky.

The dewpoint, the standard meteorological measure of humidity, could reach 75 degrees during the heat wave. “That is rare,” Chapulsky said.

The ideal temperature to keep your thermostat at during the summer is 78 degrees, according to various energy companies, including New York's Rochester Gas and Electric Corp. and National Grid.