Atlanta , Georgia ( CNN ) -- Snow and ice dealt a major blow to U.S. air travel Thursday , while much of the nation shivered from record low temperatures . At least 400 flights at Chicago , Illinois ' , O'Hare International Airport were canceled . Arriving flights were being delayed an average of 45 minutes and outgoing flights about 30 minutes , according to the Federal Aviation Administration . Chicago 's Midway Airport and Newark International Airport in New Jersey also reported delays . Those bottlenecks were affecting flights at many other international airports . Meanwhile , the National Weather Service was keeping an eye on a dangerous mix of ice and snow expected in the Southeast , where temperatures have dipped between 10 to 35 degrees below normal for the past two weeks , said CNN meteorologist Jacqui Jeras . Atlanta-based Delta Air Lines offered to issue winter weather travel waivers to Delta and Northwest passengers on flights to , from or through five states . Travelers can change their schedule without fees until Saturday if their routes include Alabama , Arkansas , Georgia , Mississippi or Tennessee . The arctic blast that began last weekend has been blamed for at least seven deaths across the nation . Share your photos , video of winter weather . Record-breaking lows were forecast for two-thirds of the country , for most areas east of the Rockies . For some regions , even lower temperatures are on tap through the weekend , forecasters said . `` But the brunt of the cold air will ride down the Mississippi River , '' said CNN meteorologist Rob Marciano , reporting from Memphis , Tennessee . Marciano said temperatures have been the lowest there in more than a decade . `` You have people not used to this weather , and homes are not built for this weather . Yesterday alone , the city [ Memphis ] went around to turn on the heat for homes when people have not been able to pay [ their utility bills ] . '' Alabama issued a warning to drivers Thursday night , urging them to stay off icy roads as driving conditions were `` becoming dangerous '' with numerous accidents reported . Trooper Curtis Summerville with the Alabama State Patrol said the biggest problem on the roads was black ice on overpasses and bridges . But , he said football was helping keep people at home as University of Alabama fans cheered on their team in the National Championship Game against the University of Texas . A wind chill advisory was in effect until Friday in Arkansas , where readings were expected to drop below zero with winds of over 30 mph . A dusting of snow in Atlanta on Thursday night left roads slick after two weeks of below normal temperatures . CNN meteorologist Chad Myers noted that it was warmer in Fairbanks , Alaska , than it was in Atlanta on Thursday morning , calling the cold front sweeping the nation one that `` we probably have n't seen for 15 years . '' 29-car pileup near Atlanta airport . In the Deep South , Florida was under a state of emergency because of the threat to the state 's lucrative citrus and vegetable industries . Gov . Charlie Crist issued an order Tuesday aimed at helping farmers salvage what they can by lifting weight limits on trucks so already-harvested crops can more easily reach markets . Also suffering in the cold : sea turtles . Florida Fish & Wildlife officers have rescued 120 sea turtles after water temperatures in the 40s shocked their tropically inclined systems , according to CNN affiliate WPBF . `` Their bodies are shutting down because they 're too cold , '' Karrie Minch of the Merritt Island National Wildlife Refuge told WPBF . `` If we do n't rescue them , they 'll end up expiring . '' Elsewhere Thursday , the high in Bismarck , North Dakota , was around 11 degrees below zero , with a wind chill of minus 35 . Forecasters said the wind chill could dip to 52 degrees below zero overnight . Snowfall amounts of 4 to 8 inches were forecast Thursday for the upper Plains to the Northeast and as far south as Kentucky and Tennessee . Up to 7 inches fell in parts of Illinois . School districts in Omaha and Lincoln , Nebraska , called off classes Thursday and city governments reported burning through their entire snow removal budgets with a full two months of winter left . Jeras said the long stretch of cold weather in the South is `` extremely unusual . '' Dallas , Texas , where it was 24 on Thursday , has been experiencing the longest stretch of cold weather in more than a decade , she said . The Southeast is expected to see lower temperatures by Saturday . CNN 's Jim Kavanagh , Craig Johnson and Ed Payne contributed to this report .
About 100 flights at Chicago Midway International Airport canceled . Expected high in Bismarck , North Dakota , minus 11 , wind chill as low as minus 35 . At least 20 deaths attributed to deep freeze , which is reaching record lows in some areas . In Nashville , Tennessee , city officials turn on heat for those who ' n't pay utility bills .