CHICAGO — Across the southern half of Chicago on Sunday, weather spotters were confirming instances of thundersnow while points west and north obliterated half-inch snowfall forecasts, with nearly 5 inches reported at O'Hare International Airport, meteorologists said.
The National Weather Service originally expected light flurries to fall on the greater metropolitan area, but Todd Kluber, a meteorologist with the weather service, said O'Hare reported 4.8 inches as of 4 p.m.
"Midway (Airport) did just include a report of thunder along with the snow," Kluber said. "We've had scattered reports of it, mainly across the south half of the city."
As of 3:30 p.m., a volunteer weather spotter reported 4.1 inches of snow near Midway, Kluber said.
Thundersnow is rare because it requires relatively warm air, which isn't all that common in storm systems cold enough to drop snow, explained Kevin Donofrio, a meteorologist.
"It's uncommon to get thunder in a winter system because the surface temp tends to be really cold," Donofrio said. "It takes a very dynamic system in order to combine the warmer air aloft — relatively warm, that is — with really cold air. You don't often get that setup in winter."
The unseasonable storm also led to more than 1,000 flight cancellations at O'Hare and Midway. As of Sunday night, 1,030 flights were called off at O'Hare, which also saw average delays of 34 minutes for departing flights, according to the Chicago Department of Aviation.
A Twitter account for O'Hare wrote that spring snow was to blame for the problems. "Snow teams & Deicers are rolling, but be sure to check flight status with your airline!" the tweet said.
At Midway, 164 flights were cancelled and average delay times clocked in at 27 minutes for departing flights, according to the department.
Though the snowfall let up by evening, Kluber said that Chicagons should expect to encounter icy sidewalks until at least Tuesday. That's because much more snow fell than originally was predicted and temperatures are not expected to warm up much until Tuesday. The snow in the city likely will melt sooner than the areas to the west that saw greater accumulation, he said.
Kluber said most roadways inside city limits were wet as of Sunday afternoon, because the snow was melting on contact with the ground. But areas to the west and northwest, including portions of Kane and DuPage counties, had slick roadways with accumulation, Kluber said.
"In those areas, snow was coming down so hard it caused some hazardous conditions," he said.
Heavy bands of snow started falling throughout the region before 9 a.m., prompting the Cubs to postpone their home game against the Angels.
Fans of HBO's "Game of Thrones," which Sunday is to air the first episode of its final season, made jokes on social media about the show's popular line "winter is coming."
Others posted memes about Chicago's "12 seasons" or references to a week that featured all four seasons in a span of just a few days.
Forecasters also were calling for an unseasonably chilly high temperature of 38 degrees. It was expected to be breezy to windy all day, with winds from the north or northwest, and with gusts as strong as 30 to 40 mph expected into the evening.
On Monday, the high temperature should return to a more springlike 47 degrees. Light rain showers are also possible Monday, forecasters said.
Although midweek temperatures are expected to rebound from Sunday's low, high temperatures shouldn't top out above 65 degrees and lows in the 40s will persist through Friday, according to the National Weather Service forecast for Chicago.