A fast-moving winter storm will unload a messy mix of heavy snow, strong winds and frigid temperatures across parts of the Midwest and Northeast over the weekend.
More than 100 million people are under some form of winter storm watch, warning or advisory from Missouri to Maine.
Snow was piling up Saturday morning in Chicago, Detroit and Cleveland. Chicago could see 9 inches of snow by midday, the National Weather Service said.
Indianapolis was to get a messy mix of rain, snow and freezing rain Saturday morning, but it was expected to turn into snow by afternoon.
Cities on the storm's southern edge such as Houston, Memphis, Tennessee, and Jackson, Mississippi, woke up to thunder and lightning Saturday.
As the storm quickly pushes east, forecasters expect a substantial amount of precipitation Saturday evening through Sunday up and down the East Coast.
A mix of snow and sleet will begin Saturday afternoon in New York and Philadelphia but shift to rain overnight. Boston will start with snow in the afternoon, followed by snow, ice and rain overnight through Sunday.
Inland areas of the Northeast and New England will likely see the most accumulation, with up to 2 feet of snow possible.
New York Gov. Andrew Cuomo said a ban on tractor-trailers and buses on most highways in the state will start at 3 p.m. ET Saturday.
Amtrak said it will operate a modified service Saturday and Sunday due to the weather.
Travel will be affected through Sunday, with more than 2,700 flights involving domestic airports canceled, according to the flight-tracking site FlightAware.com. Airlines are issuing waivers for travelers in the Midwest and Northeast.
Eppley Airfield in Omaha, Nebraska, closed for several hours Friday after a Southwest Airlines flight went off a runway while taxiing. The plane slid onto a runway overrun area, Southwest said.
None of the 150 passengers and six crew members was injured, it said.
Icing is possible in New England
Significant amounts of ice is likely along and north of the Interstate 95 corridor through New England. More than half an inch of freezing rain could fall between northern New Jersey and southern New England.
Some parts of Connecticut, Massachusetts, New Hampshire and Maine could get an inch of ice, likely triggering power outages and hazardous road conditions.
New Jersey Gov. Phil Murphy declared a state of emergency beginning at noon Saturday. He told residents to stay off the roads and prepare for possible power outages.
Severe storms possible in the South
More than 10 million people face a slight risk of severe weather Saturday in the South. The potential for dangerous weather stretches from Louisiana to Florida and north to Tennessee.
The main threats are damaging winds and isolated tornadoes.
A tornado watch is in effect for parts of Louisiana and Mississippi through Saturday morning, meaning conditions are favorable for a tornado to develop.
Deep chill across the United States
Behind this storm, a deep chill will grip much of the eastern half of the United States.
Temperatures are expected to drop so fast in some areas that any moisture on the ground or surrounding objects would likely freeze.
Highs on Sunday in the Kansas City, Missouri, area -- where the Chiefs will be host to the New England Patriots in the AFC Championship game -- will be in the 20s.
The extreme cold follows the storm and moves into the rest of the Eastern United States on Monday.
Monday's forecasted high in Boston is 11 degrees Fahrenheit, and New York City will top out at 14 F. The Massachusetts Emergency Management Agency is warning residents the wind chill could drop as low as 20 degrees below zero early Monday.
This arctic air will spill out across the country later next week as far south as Florida, leaving most of the continental United States with below-average temperatures.