PHOTOS: Thundersnow! strikes Chicago
"Our brief fling with spring is over," National Weather Service Meteorologist Richard Castro said. And as temperatures plunge this weekend and next week, piles of malleable snow will freeze into glaciers, and puddles will become sheets of ice, Castro said.
"Cold weather is back, and it looks like it's here to stay for a while. Highs in the lower 20s and teens are expected next week ... it will be very, very, very cold for this time of year," Castro said.
The weather accelerated long-awaited melting and added to considerable runoff, raising concerns about flooding.
The snow that piled up in Illinois during weeks of subzero temperatures started to melt in earnest as temperatures rose above freezing on Wednesday and Thursday. As work crews scrambled to clear catch basins of water to prevent flooding, some people took steps to make sure protect their belongings from any floodwaters. Emergency workers evacuated dozens of residents from a nursing home in Illinois' Kankakee County as a precaution.
"It flooded in front of my house up to my boot," said Lisa Robertson, a 50-year-old computer operator, after she got off a train in Chicago from her home in the south suburbs. "Last night, we made sure nothing was on the floor of the basement, (but) I'm worried about flooding when I get home."
As of Thursday afternoon, those fears had not materialized.
"It seems like it rained less here than we expected, and we are not getting the flow of water and ice melt that we expected," said Jim Zay, chairman of the Stormwater Management Planning Committee in DuPage County.
Meanwhile, river gauges along some of the nation's biggest inland waterways - the Mississippi, Missouri and Ohio rivers - showed no immediate cause for alarm. Many of those rivers, traditionally low this time of year, were expected to rise into the middle of next week because of recent snowmelt and rainfall, though National Weather Service hydrologists say those water levels are still far below flood stage.
Even the fact that the rivers have not risen all that much has provoked worry.
"It tells us the water is trapped in the snowpack," said Kent McKenzie, emergency management coordinator in Lake County in northern Illinois. "We are hoping the water gets to the rivers before tonight," when the rivers could refreeze. "If it refreezes, it puts us at a higher risk of flooding when the temperatures do rise again."
The tantalizing spell of mild temperatures will soon be gone. The National Weather Service predicted that temperatures in Illinois could fall as low as 12 degrees on Saturday night and as low as 6 degrees Sunday night.
Illinois State Police warned that the quick refreeze could result in slippery conditions on roadways and bridges.
"Even though you don't see anything," state police spokeswoman Monique Bond said, "it is treacherous."
The Sun-Times Media Wire contributed to this report.