It was a frigid Friday morning as the city logged the season’s first official subzero low. The mercury plunged to minus 6 at O’Hare and coupled with gusty west winds dropped area wind chills as low as 30 below. Afternoon highs struggled to into the single-digits as a area of light snow spread across the region. Even though most areas received less than an inch of snow, the cold pavements quickly iced over, creating a slow and perilous evening rush hour. It’s only going to get worse as a developing storm system threatens to bring a significant snowfall to portions of the Chicago area late Sunday night into Monday with a wintry mix south of the main snow area The coldest arctic outbreak to hit the Chicago area in 25 years will follow the snow. Strong northwest winds will send the mercury tumbling below zero on Tuesday afternoon for an extended period that is not expected to end until Friday. During this deep freeze, many area temperatures will likely drop below minus 20 and coupled with strong northwest winds produce life-threatening windchills of 50 below zero.