A short-lived heat blast across the Midwest and Mid-Atlantic overlaps with scheduled power plant shutdowns for seasonal maintenance on PJM Interconnection's grid, which serves 67 million people from the Mid-Atlantic to Chicago. PJM was forced to declare a low-level emergency for Tuesday and Wednesday as 60 gigawatts of capacity remained offline.

Bloomberg reports that the squeeze sent spot power prices skyrocketing across PJM's Western hub to $1,021 per megawatt-hour Tuesday afternoon, more than double the day-ahead average for that hour. Day-ahead prices for Wednesday jumped 28% to $295.83 per megawatt-hour, the highest daily average since mid-July. 

"Unpredictable weather patterns are providing fewer days to perform important maintenance or construction on the generation and transmission equipment serving our footprint," PJM spokesman Jeffrey Shields told the outlet in an email.