With December about to end, it may be a bit chilly outdoors. But some methods of providing comfort and a warm start to the day are not advisable, the Prince George’s County police suggested Monday after four cars were stolen in a single morning.

“Cold out?” the police department asked in its Twitter feed before issuing an admonition: “Don’t warm up your car” while leaving it unattended.

The four cars taken Monday were left empty and running, officers said. “We can prevent these” thefts.

Details of the thefts were not available immediately.

It was cold Monday morning, but many days this month have been colder. At Reagan National Airport, the morning low temperature was 39 degrees, which is seven degrees above the normal there for Dec. 30.

However, at the National Weather Service’s measuring site at Camp Springs in Prince George’s, the morning low was 35 degrees.

Forecasts indicated that it might get colder from Monday night into Tuesday morning, with temperatures around the Washington area dipping into the 20s.

Temperatures were falling quickly Monday night. At 7 p.m., they went as low as 33 degrees at Camp Springs.

Readings fell to 34 at Dulles International Airport. Both figures presaged a cold morning Tuesday.

Low readings in the 20s are also expected for New Year’s Eve, according to a Weather Service forecast.

Despite a few truly frigid days, this month has been one of Washington’s warmer Decembers. With only one day left in this month and year, the average temperature for December is more than 2.5 degrees above the normal figure for Washington.