Whatever the temperature outside, parked cars heat up quickly in the sun. Their metal frames work like a solar collector to raise the temperature and turn the interior into a giant oven.
Even when you think it’s cool enough outside, don’t leave your dog alone in an enclosed car. A parked car in the shade also can get very hot very quickly. And leaving a window open a crack doesn’t help.
According to research from San Francisco State University, when the outside air temperature is a mild 70 degrees, within 10 minutes the temperature inside a parked car will rise to 89 degrees. After 40 minutes, it shoots up to 108 degrees and it’s likely the dog will die of heat stroke.
When it’s 90 degrees out, just 10 minutes in a car can be fatal to a dog.