A tweet from @JayHDick about possible broken air conditioning on his Yellow Line car this a.m. reminded me that when the outside temperatures climb in the D.C. region, so too, do the temperatures on Metro rail cars.

This week, Metro boss Richard Sarles offered some data on hot cars. It’s not your imagination — there are more this time of year. In July, he told members of the Washington Metropolitan Area Transit Authority that about 2.5 percent of the cars in service experienced temperature control issues after they entered service.

Such a small number on paper, but to some passengers riding the system, it may feel like they draw the hot car approximately 100 percent of the time.

As Metro officials explained to The Post’s Dr. Gridlock, it’s hard to keep cars cool when the temperatures climb.

A properly functioning air conditioning system should cool the car by about 25 degrees, Dr. Gridlock wrote. During very hot days, such as the ones he chose for his temperature test, cars with constantly opening doors and crowds of passengers can’t keep up. And so a car that leaves the yard with an acceptable temperature but with equipment that isn’t performing well is likely to be a hot car by the afternoon commute.

You can report a hot car to a Metro train operator by using the intercom. You’ll need to know the car number, which is in black letters near the intercoms. You can also let us know by tweeting or by sending an e-mail to transportation@washpost.com — and we’ll send them along to Metro officials.

Also, check out Dr. Gridlock’s tips on how to spot (and avoid) getting stuck in a hot car.