The brutal, unrelenting cold that lasted for several days over the Christmas holiday froze off a sizable portion of Appalachia’s ample gas production, cutting off supply to power plants when they needed it most. Gas transmission pipelines said the gas they were promised simply didn’t show up. On the electric grid that connects Pennsylvania to 12 other states, at one point almost 25% of the capacity on the system either didn’t start up or broke while operating, leaving coal and petroleum-fired units to pick up the slack. PJM, a Valley Forge-based grid operator, is still analyzing what happened during the...