(Bismarck, ND)  --  North Dakota utilities are keeping the lights on for their customers during the latest cold snap.  Demand for electricity has skyrocketed and cold temperatures have disrupted the supply of natural gas in the South, leading one of North Dakota's regional grid operators to implement limited rolling blackouts in some southern states.  The state's rural electric coops have been asking large customers to switch to backup gas or diesel generators to lighten the load and prevent blackouts.