A powerful cold front (or polar vortex) developed in the United States and Canada beginning December 21. After strengthening over the Northern Plains, it descended and covered much of the eastern two-thirds of the United States from December 23 to December 25, bringing dangerous cold, high winds, and blizzard conditions to many areas.

Early indications are that the combination of unexpected high demand and failure of a significant amount of generation to perform as expected during this period pushed many regions into emergency operations. Many regions declared emergencies, and load-shedding occurred in Tennessee and the Carolinas.

As a first-order analysis, in the following infographic, we look at selected regions’ fuel mix during the event.