According to the US Army Corps of Engineers, it is unsafe to engage your parking brake in cold temperatures.
The emergency brake cable can become frozen and fail to release when the lever is disengaged. Parking in a garage or other protected area can help you to avoid this problem. But if you have to park outside and it freezes up, you should not attempt to drive your vehicle. Solutions include waiting it out or jacking up the car and using a hairdryer. The best option in freezing weather is to simply not use the emergency brake at all.