Axios

A massive, severe storm system that's slamming the U.S. Northeast with heavy snow has this weekend triggered flash flood warnings in West Virginia, Virginia, Tennessee and Kentucky, where officials reported at least 11 deaths.

The big picture: The multifaceted storm that began Saturday knocked out power to an estimated half a million customers from Virginia to Mississippi and delayed thousands of flights during the holiday weekend.

A week-long, unusually cold Arctic outbreak will bring frigid conditions to most locations east of the Rockies starting today. For some locations, this could be the coldest air so far this season.

Why it matters: This event is likely to be more intense than the two previous polar vortex-related cold snaps in the U.S. so far this winter, according to University of Oklahoma meteorologist Jason Furtado.