More than 800,000 customers in the U.S. as far west as New Mexico were without electricity and over 10,000 flights were canceled on Sunday ahead of a monster winter storm that threatened to paralyze eastern states with heavy snowfall.

U.S. airlines canceled flights and waived change fees for travelers as a cold snap and massive winter storm were forecast to sweep across the country.

The snowfall from a winter storm is expected to impact much of the nation Friday and has triggered thousands of flight cancellations.