West northwest flow in the low levels of the atmosphere will continue to bring cold air into southern Wisconsin for tonight into Saturday.
The illustration below shows the colder temperatures settling into southern Wisconsin at 850 mb, or about 5000 feet above ground level:
Clear skies and weakening winds tonight will result in a rapid temperature drop, eventually bottoming out in the single digits above zero across most areas. Locations next to Lake Michigan may be a degree or two warmer. Despite the coldest low temperatures of the season so far late tonight and early Saturday morning, these temperatures will still be far off the record books. The record low for December 10th in Madison is -16 degrees F, set in 1919. The record low in Milwaukee is -9 degrees F, set that same year. A lack of a significant snow cover is preventing temperatures from getting much colder.
This period of cold weather is expected to be short lived. The low level winds will switch back to the southwest Saturday into Sunday, resulting in moderating temperatures by Sunday. Highs in the upper 30s to lower 40s are expected Sunday across the area.
Here is how the forecast for the weekend is shaping up for southern Wisconsin: