This is an archived article and the information in the article may be outdated. Please look at the time stamp on the story to see when it was last updated.CHICAGO — The Chicago River is starting to flow once again, chunks of ice slowly starting to melt as a 70-degree swing in temperature in just four days brings a feeling of spring to Chicago. “it’s like spring – springtime in Chicago, everybody comes out,” courier Matthew Balkzekas said. The polar vortex brought dangerous sub-zero temperatures, and some of the coldest weather the Chicago area has seen in decades. Since then, the city has seen a 71-degree turnaround in temperature from Wednesday’s minus 25 to Sunday’s 46. In 72 hours, the steam sweeping over a rock solid Lake Michigan is gone, and there are cracks in the ice. Joggers who were bundled in snowpants have shed everything but the shorts. For those who had to work outside in the bitter cold last week, the warm up was especially welcome. And it could to get even warmer tomorrow.