By Josh Levs and Ben Brumfield
(CNN) -- A massive winter storm spanning 20 states could dump as much as 1½ feet of snow in some places Thursday and bring life to a standstill in parts of the central United States.
About 60 million people -- 20% of the U.S. population -- are under winter weather warnings, watches and advisories in the 750,000 square miles affected.
Dodge City, Kansas, "is in the middle of a bull's eye," said CNN meteorologist Chad Myers. The state should see 16 to 18 inches of snow west of Wichita, with the white stuff continuing up into Nebraska.
United Airlines announced Thursday that certain affected travelers can change their itineraries without paying fees.
Statewide emergency declared
Missouri Gov. Jay NIxon declared a state of emergency. Snow, sleet and ice could wreak havoc, and parts of the state could see more than 10 inches of snow.
Kansas City, Missouri, Mayor Sly James also declared a state of emergency. There were 250 snow plows working to clear roads in the city, but residents were urged to limit travel.
Kansas City International Airport announced that some flights were canceled and called on passengers to check on their flights before venturing to the airport.
The city could have its highest daily snowfall since 1912 on Thursday if the prediction of nearly a foot of snow pans out, CNN meteorologist Brandon Miller said.
CNN iReporter Joseph Kopel posted photos of empty shelves in St. Joseph, Missouri, on Wednesday as people stocked up for the blizzard.
Kansas State University canceled Thursday classes, as have dozens of grade schools in the Plains states.
In Wichita, crews have spread salt and sand across roads since Monday. But no matter how much they used, many roads remained slick. Side streets were worse, CNN affiliate KSN reported.
Across Kansas, authorities were calling on people to "just stay home," the station reported.
Wichita set a record for daily snowfall Wednesday, with 6.2 inches.
Some drought relief expected
There is a silver lining for some areas facing the heavy snowfall. "Big chunks of Nebraska, Kansas, Oklahoma and Texas" are facing exceptional drought, HLN meteorologist Bob Van Dillen said.
"You squeeze out the water from the melting snow, and you're talking 1 to 2 inches of water for those dry regions."
On Wednesday, CNN iReporter Doug Simonton in Tulsa, Oklahoma, posted a photo of a car covered in snow and said numerous traffic accidents had been reported around town.
A large system
The storm system is huge and carries with it a warmer, wetter Southern component.
It will eventually stretch from the Dakotas to Houston, Myers said. While it will remain snowy in the north, the system will spawn torrential rains and tornadoes along the Gulf Coast and dump freezing rain over Arkansas and Missouri.
"There's going to be a monster ice storm over Springfield and Branson, Missouri. Think of an inch of ice coating everything," Myers said. "Power lines will be coming down. Trees will be coming down."
In St. Louis, freezing rain is predicted to fall on top of a thin layer of snow, which will have "a significant impact on travel," the National Weather Service warned.
North of where the most snow will fall, Chicago could receive as much as 6 inches, CNN's Sarah Dillingham said. The city is running 15 inches below its average snowfall for the season.
Severe thunderstorms moving in from the Gulf of Mexico are expected to dump from 2 to 6 inches of rain over New Orleans and Montgomery, Alabama, according to CNN's weather center, before rolling up toward Atlanta.
The torrential rains could lead to significant river flooding, as flood watches are still in effect from last week's heavy rains.
Heavy winds, hail and tornadoes are possible, the National Weather Service said. Downpours are expected to continue into Friday.
Desert dwellers stunned
On Wednesday, the winter storm system left a rare thin layer of snow across the deserts of Arizona, New Mexico and Southern California -- as far south as the border with Mexico.
"I've been here for over 10 years and I've never seen it snow like this," Kayla Avery of Tucson, Arizona, said in a CNN iReport, which came with a video of the snowfall.
"There is more snow on the ground in Tucson today than I have seen in over 30 years living here," Carrie Tucker said in another iReport.
Mona Jensen of Dolan Springs, Arizona, posted photos of her 8-acre property blanketed by snow.
Katie June in Yucca Valley, California, shared a shot of a snow-covered cactus.
"Some of the larger ones are having a hard time," she wrote. "But they all enjoy the drink!"
CNN's Steve Almasy, Mike Pearson and Pedram Javaheri contributed to this report.