Extreme weather hits U.S., from blizzards to an early heat wave.

A broad storm system on Monday brought blizzards, severe storms and an unusually early heat wave across large parts of the United States, disrupting flights and causing widespread power outages.

A broad storm system on Monday produced a mix of extreme weather across the United States, including heavy snow in the Midwest, severe storms on the East Coast, and unusually warm conditions in the Southwest. Officials reported significant travel disruptions, widespread power outages and active wildfires in affected areas. Federal offices postponed some business and agencies sent workers home early as the system moved through multiple regions. Key developments: - More than 4,700 flights were canceled nationwide, and tracking service FlightAware reported over 2,100 cancellations or delays as of 6 a.m. - Poweroutage.com reported over 500,000 customers without power, mainly in Michigan, Pennsylvania, New York and Massachusetts. - Blizzard and heavy-snow conditions affected parts of the Upper Midwest and Great Lakes, with some communities receiving about three feet of snow since Saturday. - A heat dome pushed temperatures into the 90s and triple digits in parts of the Southwest and California, while three fires in Nebraska had consumed more than 1,140 square miles of mostly grassland. Summary: The system disrupted travel, caused widespread outages and prompted local officials to delay or postpone some public business. Undetermined at this time.