Cold to linger through the weekend, then mild

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Friday’s high of 9 degrees at O’Hare International Airport equaled the high on December 15th, tying it as the lowest maximum temperature of the season. This latest single-digit high was more remarkable, considering that it occurred on a day with partial sunshine, and in the absence of snow cover. An extended cold snap in December, combined with our ongoing push of polar air, has lowered this winter’s average temperature to 24.1 degrees, ranking it among the city’s coldest 20 percent of winters since 1871. This season is also running 13 degrees colder than a year ago. These chilly statistics will be modified in coming days. Forecasts show a major pattern change is to begin by Monday. Jet stream flow from the Arctic is expected to transition to a coast-to-coast westerly stream by Tuesday, sweeping mild Pacific air into the region.