A giant storm is expected to test the entire U.S. power grid this weekend.

As a massive storm advances towards the northeast of the United States, heavy snow and dangerous cold are spreading from the Rocky Mountains to the Great Lakes region, causing transportation disruptions and threatening the power supply in most parts of the country. The storm is expected to bring heavy snow, destructive freezing rain, and subzero wind chills to some of the biggest cities in the US; airlines have already canceled flights, and Amtrak has removed some trips from its schedule. State and local officials have warned residents to prepare for power outages, frozen pipes, and road closures; due to concerns that equipment freezing will disrupt supplies, electricity and natural gas prices have soared significantly.