( CNN ) -- When she was very young , Kayla Avery was used to playing in the snow . But the former Boston resident had n't seen much of the white stuff since she moved to Arizona more than a decade ago . She got a reminder Wednesday . `` We received a blizzard warning last night through the emergency broadcasting system . Most of us did n't believe it , '' she told CNN iReport . `` Most of the news reports said it probably would n't snow in the valley , and two hours later it was snowing . '' Avery , a 19-year-old student at the University of Arizona , said the snow was still falling Wednesday afternoon . `` My brother and I were staring out the window saying , 'What ? It 's snowing in Tucson ? That 's not supposed to happen ! ' `` she said , adding that she 's never seen this much snow in the area since her family moved there . Usually the area gets no more than a dusting of snow once a year . iReport : `` Blizzard '' in Tucson . The inch of snow also caused PGA Tour officials to postpone play at the World Golf Championships-Accenture Match Play Championship in nearby Marana , Arizona . The rare accumulation was all part of a massive winter storm that promises to blanket a huge swath of the nation in crazy weather , from 18 inches of snow or more in Kansas to thunderstorms and flooding along the Gulf Coast . Trouble for the next three days . In all , about 800,000 square miles in 18 states were under some form of watch or warning Wednesday related to a major storm pouring out of California and into the Central Plains and the Midwest , CNN meteorologist Brandon Miller said . About 30 million people live in the covered areas , he said . One of the places that could be hit the hardest is Springfield , Missouri . Among the hazards expected there Wednesday : lightning , wind and ice , with a little snow and sleet thrown on top for good measure . The biggest threat of heavy snow lies in parts of Kansas , Nebraska and Missouri , with the possibility of whiteout conditions in some places , he said . Track winter weather across the U.S . In Kansas , where the storm had already started , the National Weather Service was predicting as much as 18 inches of snow . The agency said parts of Nebraska could see more than a foot of snow , with drifts making some roads impassable . CNN affiliate KSNW in Wichita reported that crews had treated roads Monday but no matter how much salt and sand they had spread , by Wednesday morning , primary roads were snow-packed and slick . Side streets were worse . There was a break in the weather that allowed crews to get out before the afternoon rush hour and clear some of the major thoroughfares , the station reported . Kansas State University announced on its website that Thursday classes were canceled . Forecasters were predicting as much as 2 inches of snow in St. Louis , with the precipitation turning into sleet and freezing rain Thursday . The conditions will have `` a significant impact on travel , '' the weather service warned . North of where the most snow will fall , Chicago could receive what would be its largest single snowfall of the year -- 4 inches , Miller said . The city usually gets up to 4 feet of snow a year . So far this year , only about a foot has fallen , he said . South of the snow belt , dangerously icy conditions are possible in parts of northern Arkansas and southern Missouri , he said . That includes Springfield , where windy conditions will precede the possibility of up to 3 inches of snow and sleet Thursday , with the possibility of a quarter of an inch or more of ice to boot . Heavy rains forecast . Elsewhere , severe thunderstorms moving in from the Gulf of Mexico are expected to dump from 2 to 6 inches of rain over New Orleans , Louisiana , and Montgomery , Alabama , according to CNN 's weather center , before rolling up toward Atlanta . The torrential rains could lead to significant river flooding near the Gulf , as flood watches are still in effect from last week 's heavy rains . Heavy winds , hail and tornadoes are possible , the National Weather Service says . Downpours are expected to continue into Friday . Travel delays . It was snowing Wednesday in Denver where almost a dozen inbound flights were canceled , according to the flight-tracking website FlightAware.com . More than 200 flights into or out of U.S. airports were canceled , the website said , with almost 175 already called off for Thursday . Kansas City International Airport posted a statement on its website advising passengers to check their flight status before heading to the airport . `` There is potential for more cancelled or delayed flights as the storm continues , '' the statement said . Flight Aware reported that more than 100 flights were affected at that airport . CNN Meteorologists Ivan Cabrera and Dave Hennen contributed to this report .
More than 200 U.S. flights canceled on Wednesday . Parts of Missouri and Kansas could see 3 inches of sleet , 1/4-inch of ice . The storm is expected to move into the Midwest by Thursday night or Friday morning. There are still flood watches in place from last week near the Gulf , and more rain is coming .