Chicago-area ComEd customers warned rolling power outages are possible Christmas Eve, Christmas Day

CHICAGO - ComEd warned electricity customers in the Chicago area that hours-long rolling power outages were possible on Christmas Eve and Christmas Day – two of the coldest days so far this winter.

ComEd said the power outages – if they happen – would be due to problems with PJM Interconnection. PJM coordinates the movement of wholesale electricity and ensures power supplies for 65 million people in all or parts of 13 states and Washington, D.C.

Iif rolling power outages are needed, a city official said the first customers impacted would have about 15 minutes notice. The next power outage areas would be given 1 to 2 hours notice. Customers could be without power for 2 hours.

"While PJM will do everything in its power to prevent rotating outages, the risk is real and we ask consumers to continue conservation efforts," PJM said on Twitter.

PJM and ComEd said that customers can help reduce the burden on the power system – and lower the risk of power outages – by setting thermostats lower than usual, if health permits; postponing use of major electric appliances such as stoves, dishwashers and clothes dryers until other times; and turning off non-essential electric lights, equipment and appliances.

The strain on the power grid is expected to lessen by 10 a.m. on Christmas morning.

An earlier version of this story quoted ComEd as saying that customer would get 15 minutes to 2 hours notice. That information was from a Chicago city official, not ComEd.