Tests have shown that the majority of the temperature rise can occur within 15 to 25 minutes.

As shown in the chart left, on an 85º F day, the temperature inside the car
can reach 110º in less than 20 minutes.

In 5 minutes, it can climb to 95º F

Humidity also plays a critical roll.
(Dogs become less efficient at cooling themselves as the humidity rises). A dog's normal body temperature is about 101.5 degrees. But during a heat stroke, it can rise to 105-110 degrees with tragic results. As shown in the chart, this temperature can be reached very quickly, even when the temperature outside is only 85 degrees F.