A view of Lake Michigan during subzero temperatures in Chicago on Friday. (@NatalieCB_ via Reuters) (Social Media/Reuters)

Mother Nature can’t make up her mind in the Midwest and Northeast, where a number of locations have set record-high temperatures — just days after a polar blast brought a rash of record lows.

The lobe of the polar vortex, which carried punishing cold air into the Midwest and Northeast Wednesday through Friday, swiftly retreated over the weekend, and a surge of unseasonably mild air took its place.


High-altitude weather pattern simulated from the European model Wednesday and Sunday. (PivotalWeather.com)

The magnitude of the thaw has been remarkable and, in some places, record-challenging.

Wednesday, the temperature at Chicago’s O’Hare International Airport plummeted to a staggering minus-23, climbing to minus-10 in the afternoon. It was the city’s second-coldest day in recorded history. The minus-23 was the coldest since 1985.

Fast-forward to Sunday. The low temperature sank to 39 degrees, the warmest for Feb. 3 on record and a 62-degree swing from Wednesday.

On Monday, Chicago’s temperature raced into the low 50s. Considering the wind chill in Chicago crashed to minus-50 on Wednesday, the city witnessed a 100-degree swing in the feels-like temperature in five days.

Chicago’s not alone in its remarkable temperature turnaround. Nearby Rockford, Ill., shattered its record low, plummeting to minus-31 on Thursday. The previous record of minus-27 had stood for nearly four decades. Four days later, on Sunday, the low in Rockford didn’t drop below 37 degrees, a record for the date — and was a 68-degree swing.

Buffalo was home to another wild fluctuation. It set a record low on Friday of minus-4. Then on Sunday, it set a record high, peaking at a balmy 54 degrees.

While the short-fused spike in temperatures has been impressive in many areas, La Crosse, Wis., might take the cake. Its temperature soared 73 degrees in three days. The National Weather Service office serving the region tweeted it was the greatest 72-hour leap in temperature since 1951. Thursday morning saw a low of minus-33, before a maximum of 40 on Groundhog Day.

The brief warm-up coincided with Punxsutawney Phil’s cheerful announcement of an early spring, but make no mistake — the springlike weather will not last. A cold front will knock temperatures into the 20s from the Twin Cities and Chicago south to the Interstate 70 corridor Monday night with a stronger cold front to follow late in the week.

Officials fear the rapid freeze-thaw cycle will result in burst pipes, potholes, ice jams and floods. Numerous rivers in northern Illinois were under flood advisories and warnings Monday because of the ice-jam threat.

In addition, melting has led to above-average groundwater in a large swath of the nation’s middle. The rapid drop in the mercury will lead to quick freezing of water near the surface, resulting in expansion and possible “frostquakes.”

These earthquake-like rattlings of the ground are the product of fresh snowmelt or rainwater entering shallow cracks in the ground. When the temperatures plummet swiftly, trapped water becomes ice and expands. That imparts stress on chunks of soil, building until giving way in an abrupt jolt and boom.

Above-average groundwater in Iowa, Illinois and Missouri should help to trigger frost quakes. Residents in the eastern Corn Belt may experience a few of these “cryoseisms” in the next 36 hours.

Capital Weather Gang’s Jason Samenow contributed to this report.