The mid-Atlantic electricity grid operator is asking people to conserve electricity as a wave of bone-chilling cold moves in to the Great Lakes area.

The Valley Forge, Montgomery Co.-based PJM Interconnection said Monday that conserving electricity will help ensure there's an adequate power supply.

PJM said demand for electricity is expected to be highest Tuesday evening, and it's asking people to conserve especially from 6 a.m. to 10 a.m. and from 5 p.m. to 9 p.m. on Tuesday.

It suggests people set thermostats lower than usual, if health permits, and postpone using major appliances such as stoves, dishwashers and clothes dryers until midday or after 9 p.m., when the demand for electricity goes down.

Forecasters said temperatures will be coldest around the Great Lakes and in western Pennsylvania, but the 69 News viewing area can expect high temperatures Tuesday in the middle teens and wind chills below zero all day.